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POWER ELECTRONICS 4TH YEAR ELECTIVE.
ELECTRICAL SAFETY; REV A
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ELECTRICAL SAFETY ELECTRIC SHOCK, TRAUMA &
SAFE WORKING
1
OUTLINE OF UNIT.............................................................................................................................3
2
INTRODUCTION.................................................................................................................................3
3
ARCS.......................................................................................................................................................3
4
ELECTRICAL SHOCK AT POWER FREQUENCIES .......................................................................4
5
EDF 10 YEAR STUDY ...........................................................................................................................5
6
RESISTANCE OF THE HUMAN BODY ............................................................................................6
7
CONTACT SITE MARKS......................................................................................................................9
8
VENTRICULAR FIBRILLATION & HEART CURRENT FACTOR................................................9
9
INFLUENCE OF VOLTAGE ON SEVERITY OF SHOCK ............................................................. 11
10
DELAYED DAMAGE DUE TO CURRENT FLOW.......................................................................... 11
11
ELECTRIC FENCES .......................................................................................................................... 12
12
SAFE WORKING PRACTICES........................................................................................................... 13
13
SOME ACTUAL INCIDENTS............................................................................................................ 14
13.1
13.1.1
The Incident ............................................................................................................................................................. 14
13.1.2
Contributing Factors ................................................................................................................................................ 15
13.1.3
Recommendations ..................................................................................................................................................... 16
13.2
ELECTRIC SHOCK WORKING IN CEILING SPACE ................................................................................................. 16
13.2.1
The Incident ............................................................................................................................................................. 16
13.2.2
Analysis of Incident.................................................................................................................................................. 18
13.3
14
PERSON ELECTROCUTED AFTER TOUCHING A LIVE TERMINAL............................................ 14
DEATH BY ELECTRIC SHOCK AND FALLING ......................................................................................................... 19
13.3.1
The Incident ............................................................................................................................................................. 19
13.3.2
Analysis of Incident.................................................................................................................................................. 19
REFERENCE LIST.............................................................................................................................20
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POWER ELECTRONICS 4TH YEAR ELECTIVE.
ELECTRICAL SAFETY; REV A
Revision List
A : original
Prepared by Dr K A Walshe
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POWER ELECTRONICS 4TH YEAR ELECTIVE.
ELECTRICAL SAFETY; REV A
1
PAGE 0 - 3
Outline of Unit
Detail
Duration
Comment
Electrical safety – understand what
causes electric shock; it’s magnitude
and consequences
1 unit
In an increasingly litigious industrial
environment, it is essential that the
engineer / manager is fully aware of
how electric shock occurs and how it
may be prevented.
2 Introduction
Electric shock can range to the barely noticeable tingle to massive burning bone
fracture and burning of tissue. In addition surface radiant burns are common as a
result of a persons close proximity to an electric arc.
It is therefore very necessary that persons exposed to potentially live conductors or
likely to be in control of tradesmen who are exposed to potentially live conductors
appreciate some of the factors that determine the severity of electric shock and basic
precautions to mitigate the consequence of such shock.
As an engineer / manager you are responsible for the safety of the people
reporting to you and indirectly of anybody else whom may be working in an
unsafe manner.
3 Arcs
An electric arc is formed when ever an insulated gaps between two electrodes of
differing potential breaks down. This can occur as a result of an excessive voltage
being applied to a constant gap or as a result of moving current carrying contacts
separating and arcing until the dielectric strength of the gap being created causes the
arc to extinguish (this is normal AC circuit breaker action).
The breakdown strength of air and Standard Temperature and Pressure is
approximately 30 kV/cm and there is also a requirement of there being a minimum
of 300 volts (absolute value not rms) across an airgap before breakdown can occur.
It is very difficult for any airgap to breakdown on 110 ~ 120 V AC systems
Once an arc has formed it only requires approximately 20V/cm to maintain itself.
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ELECTRICAL SAFETY; REV A
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Arcs can however be initiated at much lower voltages as a result of tracking across
insulators.
Electric arcs have core temperatures in the range 2,000 degC to 10,000 degC and
thus result in severe (2nd 3rd and sometimes 4th order burns) to anybody within a
radius of 2 ~ 3 metres away from the arc. Electricians working on live LV
switchboards are the most at risk since they will often be close to busbars having a
fault current duty of 30 ~ 60 kA.
4 Electrical Shock at Power Frequencies
The generally accepted spectrum of power frequency electric shock is :Effect Noticed
current for hand - foot shock
no perception
<1 mA
tingle
1 < I < 3 mA
mild sensation; no skin damage
pain full shock
3 < I < 10 mA
pain,
some
skin
marking,
onset of No-Let-Go Arm paralysis
asphyxiation
10mA < I < 75 mA
ventricular
fibrillation
probability level
ventricular fibrillation
75mA < I < 2.5 Amps
cardiac arrest
I > 2.5 Amps
tissue burning
I > 4.0 Amps
organ burning
I > 20. Amps
onset
0.5%
A major step change in the current that flows occurs in the range 500 V to 700 V at
power frequencies due to the outer layer of the skin breaking down by electric stress
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ELECTRICAL SAFETY; REV A
5
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EdF 10 Year study
In a study by EdF 1 (Electric de France) (the single overall generation, transmission
and retailing authority for electricity in France) over a ten year period a total of 123
electrical accidents sustained by it’s employees were recorded and analysed. EdF
employees approximately 120,000 people.
High voltage working in power authorities is normally carried out under strict preprogrammed procedures thus high voltage electric shock incidents ought to have a
lower incident in this study than in the population as a whole.
Type of incident
% of
incidents
Comment
Immediate death
2.4
in majority of cases electric current flowed through
the body and ventricular fibrillation occurred
Not immediately fatal,
loss of consciousness
apparent death
7.2
inhibition of major body functions; respiration,
consciousness but usually not cardiovascular arrest;
responds well to immediate intensive care
Initial lesions; burns
93
arc burns are most frequently observed 77% of cases.
Ocular burns are often associated with low voltage
(< 1000V) incidents
Electrothermal burns
15% of burns
cases
this is the type of burn associated with passage of
electric current in the body; extensive electrothermal
burns (deep tissue burning) seen in 10% of all
electrothermal burns cases
Mixed burns
6% of
burns
normally multi-site and associated with HV shock and
often have severe, progressive effects with major
sequelae.
Delayed onset fatalities
1%
mainly associated with extensive burns & kidney
failure also several cases of death through onset of
cardiovascular failure.
Neurological
&
psychological sequelae
7.3%
sequelae include headache, dizziness, physical or
psychological lassitude, mood and personality
disturbances
Psychological
neurovegatative
sequelae
1%
some cases of true neurotic disturbance recorded;
electric shock need not have involved the head.
3.6% of non-
ocular : 8% of arc injuries involved ocular injury
Sensory Sequelae
1
or
all
Industrial Accidents and their complications, Cabanes, J; chapter 2 Electrical
Trauma ed Lee, Cravalho & Burke, Cambridge University Press 1992
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Permanent disabilities
PAGE 0 - 6
fatal
accidents
(chronic conjunctivitis) Four cases (out of 1231) each
of corneal burns and retina burns. cataracts rarely
occur
Auditory sequelae observed in 1.3% of accidents lesion and vestibular damage.
21%
see graph of distribution of degree of permanent
disability
Distribution of Permantent Disability
by % impairment
number of cases
1000
100
10
1
0
10
20
30
40
50
60
70
80
90
100
% impairment
Figure 1 : % distribution of Permanent disabilities
It is seen from this graph that 50% bodily impairment occurred with a frequency of
1% in a population sample where high voltage shock could reasonably be expected to
have a far greater occurrence than in the general population. From this it necessarily
follows that the percentage of electric shock incidents in the general population
leading to a given level of impairment will be significantly lower than the above
graph.
6 Resistance of the Human Body
For electrical purposes the body can be thought of as a thin insulating shell
surrounding a near uniform conducting mass with long rods of poorly conducting
material (bone).
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ELECTRICAL SAFETY; REV A
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The conducting mass comprises the subcutaneous layers of the skin and all the
internal parts of the body. Typical values of conductivity are :Conductivity
Siemens/ metre
skin
3.8 * 10^-
fat
5 * 10^-4
muscle
4 * 10^-4
bone
1 * 10 ^-4
The epidermis layer can exhibit resistance values from a few thousand ohms with
young moist and / or cracked skin to many tens of thousands of ohms in older dry
skin.
In contrast to this insulating shell the inner body tends to exhibit a composite
resistance in the range from 500 Ohms to a few thousand ohms depending on the
magnitude of the applied voltage and its frequency. At power frequencies (50 ~ 60
Hz) and with sinewave applied voltage, the variation of body resistance with applied
voltage is as shown in Figure 2 below.
Prepared
Dr K
A Walshe
Figure 2 by
: Total
Body
Impedance
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It is known that the body resistance to DC is between 25% and 50 % higher than
that at power frequencies. Furthermore there is a marked difference between
sinewave excitation and impulse excitation. This has led to an equivalent circuit for
the body where the skin is a parallel Resistance / Capacitance - fig 3.
Figure 3 : Model of Body Impedance
The impedance of individual sections of the body relative to the Hand to Foot path
are distributed as :from
to
% of total
wrist
elbow
26.4
elbow
arm pit
10.9
arm pit to
top of shoulder
6.9
arm-pit
arm-pit
6.9
arm-pit
centre chest
9.9
centre chest
navel
1.3
navel
top of leg
5.1
top of leg
top of adjacent leg
8.7
top of leg
knee
14.1
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knee
7
PAGE 0 - 9
sole of foot
32.3
Contact Site Marks
The medical literature makes free use of the terms “Entry” and “Exit” sites when
talking of the electrode contact points. Some writers describe an exit site as
exhibiting an explosive exit of current; almost as if the electrons have had to burst
their way out from the body. In more recent times these terms have been recognised
as being less than accurate; their use for power frequency wounds is not so prevalent
as previously.
A contact mark will be observed depending on the current density and duration of
exposure. This is very similar to a thermal burn and hence the marks left by the
passage of current are similar.
current density
observation
< 10 mA/mm^2
no permanent change in skin; For current flow longer than several seconds
skin below electrode may become grey-white with coarse texture
10 ~ 20
mA/mm^2
reddening of skin with a white colour along the edge of the electrode
20 ~ 50
mA/mm^2
brownish colour sinking into the skin below electrode; for exposure of
several tens of seconds blisters are observed around the electrode
> 50 mA/mm^2
carbonisation of the skin occurs
NB for exposure times of less than one second, the above current densities have to nearly
double to obtain the effect described for long exposure.
8 Ventricular Fibrillation & Heart Current Factor
Ventricular fibrillation is uncoordinated pulsation of the heart which results in little if
any blood flow in the body. It is considered the main cause of death from electric
shock
Some cases of death by asphyxia and cardiac arrest are reported but the frequency is
much lower than VF.
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ELECTRICAL SAFETY; REV A
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VF occurs when the current in the range 50 mA for 1 sec to about 2.5 amps 0.04
seconds at which level cardiac arrest occurs.
If the current does not flow uniformly down the trunk of the body, then the heart
will experience a small exposure. A “Heart Current Factor” is thus defined to relate
the severity of different electrode contact sites to a full “left hand to both feet”. IEC
479 defines a factor that permits the calculation of the current Ih through paths other
than the left hand to (both) feet which presents the same risk of VF
Ih = Iref /F
where Iref = current left hand to both feet for a given risk of VF
F = factor in Table below
Current path
Heart current Factor
left hand to left or right or both feet
1.0
both hands to both feet
1.0
left hand to right hand
0.4
right hand to left foot, right foot or both feet
0.8
back to right hand
0.3
back to left hand
0.7
chest to right hand
1.3
chest to left hand
1.5
seat to left hand, right hand or both hands
0.7
If the electric current flows for 0.2 seconds or less VF will only occur if the passage
of current coincides with the vulnerable “T” periods (ventricular recovery from
excitation) of the cardiac cycle.
A particularly brave Italian engineer researched this aspect of electric shock for many
years and ultimately proved that VF could be avoided if power was removed in
30mseconds – he did this by experimentation on himself and was ultimately awarded
one of Italy’s highest honours for his work. This is now the basis of the “earth
leakage circuit breaker”.
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ELECTRICAL SAFETY; REV A
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9 Influence of voltage on severity of shock
Electric shocks have been arbitrarily divided into low and high voltage with the
boundary between the two set at 1000 V although care must be taken as some
authors have located the boundary as low as 380 Vac when differentiating between
the two “types” of shock.
It has already been seen that the body resistance remains nearly constant above about
700 V. This happens because at 700 V the outer layer of the skin breaks down very
quickly and thus the skin starts to have little effect on the overall body impedance.
Medical research has also shown2 that high electric field strengths across cells can
lead to cell membrane breakdown.
Thus in high voltage shock incidents the mechanisms of both thermal damage
leading to thrombosis (the Joule heating effect) and cell wall breakdown (voltage
stress) contribute to muscle and organ damage.
10 Delayed damage due to current flow
There has long been two schools of thought in the medical world regarding the
sequela of electric shock.
One school believed that the consequential damage to tissue developed over time
requiring long hospitalisation and repeated surgical intervention to remove dead
tissue whilst the other school held that all the damage was done at the time of the
shock and that effects that appeared later where only a manifestation of the difficulty
in identifying all nonviable tissue when the first surgical exploration is under taken.
The second school of thought advocates large scale removal of nonviable and
marginal tissue at the earliest opportunity followed by rapid wound closure to
prevent infection and encourage regeneration of muscle tissue3.
2
Lee, R.C. ; Pathophysiology and clinical management of electrical injury, in book
“Electrical Trauma” ed Lee, Cravalho & Burke, pub Cambridge Univ Press 1992
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It certainly appears true that within hours of the injury, the damaged muscles begin
to swell as the permeability of the tissues begins to change. Once fluid pressure in
excess of 30 mm Hg is observed in muscle compartments surgery is required to
prevent compression injuries to tissue and nerves.
Irrespective of the rights and wrongs of the two theories, it is clear that time is of the
essence in treating electric shock; immediate testing for excessive current ( fluid
pressure, discoloured urine etc) must be made to ensure tissue loss in minimised.
11 Electric Fences
Electric fences are regulated in Australia by reference to AS 3000 ( the “Wiring
Rules”) and AS 3014 ( Electrical installations – Electric Fences).
Apart from matters relating to the insulation between the 240V power circuit and the
HV fence circuit, the Standard places a limit on the energy per pulse and the pulse
mark to space ratio.
Based on the various
Pulse into 500 Ohms
factors already
1
discussed it is held
0.8
that a pulse of less
500 ohm load and
lasting for no more
than 0.1 seconds with
votlage per unit of 10 kV.
than 8 Joules into a
0.6
0.4
0.2
0
-0.2
-0.4
a
-0.6
repetition rate of not
more one per second
-0.8
-1
time 0 to 0.075 sec.
will cause discomfort
but no damage to the vast majority of humans.
3
Gottlieb, Saunders & Krizek; Surgical technique for salvage of electrically damaged
tissue, , in book “Electrical Trauma” ed Lee, Cravalho & Burke, pub Cambridge
Univ Press 1992
.
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This then allows voltages as high as 10 kV to be applied. The figure above shows the
current in a 500 Ohms resistive load occasioned by a 24 volt battery powered electric
fence energiser. The recording was made via a high speed 8 bit digital recorder and
this produced some in the output waveform.
12 Safe Working Practices
•
Only qualified persons are permitted by law to carry out installation work defined
in AS3000.
•
Know how to isolate all power to the work area before starting work.
•
Make sure “Others” know where you are going to be working
•
Ensure that there are no obstructions to access of work area that might make
egress difficult in the event of a fire
•
Know were the fire fighting gear is before starting work.
•
Ensure that resuscitation and first-aid facilities are nearby.
•
Have an assistant trained for electrical accidents close by and able to turn power
off quickly if required.
•
Live working (ie working on live equipment and wiring) is only to be undertaken
in the last resort and full Personnel Protective equipment must be available to the
electrician and must be used. This includes rubber mats, rubber gloves, rubber
soled shoes (boots), goggles and hard hat.
•
Test before acting and prove the test equipment before relying on it.
•
Cotton shirt and trousers (both to be full length) must be worn to minimise the
area of bare flesh that might be accidentally earthed or made alive.
•
Remove wrist watch.
•
Only use handtools with fully insulated handles and use the tool properly.
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•
PAGE 0 - 14
Regularly test the insulation on the handles with a megger; destroy any handtool
with substandard insulation.
•
All power leads to be tested and tagged as required by law.
•
Safety lock and tag off all circuits before working on them.
•
Never remove a safety lock or tag other than your own.
•
Analysis the risks inherent in a job before undertaking it (on large job sites this
will require a written risk analysis appraisal before work starts).
•
Do not let anybody onto a job site without first explaining to them what the risks
and safety procedures are.
Engineers can find themselves required to undertake testing or fault finding work
where it is impossible to predetermine what is to be done. Accidents tend to happen
due to the engineer taking short cuts such as
1. Propping an escutcheon plate in a precarious position and having it slide into live
terminals,
2. Trying to get access to dead equipment via a compartment with live busbars in it.
3. Dropping spanners down gaps into live busbars
13 Some Actual Incidents
13.1 PERSON ELECTROCUTED AFTER TOUCHING A LIVE TERMINAL
The following is an Incident Report prepared by the West Australian WorkSafe office.
13.1.1
The Incident
A crewmember on a fishing trawler died after receiving an electric shock from a live
brass terminal on an ammeter, which was located on the rear of a switchboard cover.
The fingers of his right hand came in contact with the terminal and the electrical
current passed from his right hand through his body to both feet.
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His feet were in contact with the metal floor of the vessel.
A polycarbonate switchboard housed all of the electrical circuit breakers and
overload devices for the distribution of 240/415-volt power throughout the vessel.
Because there were only two circuits for general-purpose electrical distribution and
because of demand, the circuit breakers, or thermal overload, for the entire system
would activate causing the power to shut down.
13.1.2 Contributing Factors
Additional electrical appliances had been added to the two circuits for general
purpose use, which when all were turned on simultaneously, drew more electrical
current than each individual circuit was designed to carry. This therefore created an
imbalance that caused the circuits to trip out.
The larger appliances (air conditioner, hot water system) were not individually wired
back to the switchboard to ensure that a regular imbalance did not occur when all
items requiring electricity were switched on at the same time.
The thermal overload reset button on the main contactor was located under the
polycarbonate switchboard cover and was not accessible from the outside of the
cover. The cover had to be removed to reset the button.
The screws holding the polycarbonate cover in place had been removed and duct
tape was used to hold the cover in place. At the time of the accident the duct tape
did not have sufficient adhesive on it to hold the cover in place either temporarily or
permanently.
No lock out or tag out procedure was in place to ensure the switchboard was isolated
from electrical current prior to attempting to reset any overload devices. This would
include the shutting down of the gen-set or disconnecting the shore power supply.
No-one onboard the vessel was qualified to work on 240/415-volt systems. Removal
of the switchboard cover is considered electrical work under the Electricity Act 1945.
Silver adhesive tape (duct tape) used to hold
the switchboard cover in place. The screws had been removed to obviously allow for
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simple access to (button in centre) the main contactor switch. The cover did not have
access from the outside to the main contactor (overload) switch.
13.1.3 Recommendations
•
Owners and Skippers of vessels to ensure all electrical equipment on vessels is
maintained in a condition such that no modification can expose crew to a risk of
electrocution.
•
The control of hazardous energy is the most important step in safe maintenance
of equipment. Suitable Lockout - Tagout procedures protect persons in the
workplace from unplanned energy sources from moving machinery, chemical
energy, thermal energy, pneumatic energy, stored and of course electrical energy.
•
Compliance with Australian Standard 3000 - 1991 SAA Wiring Rules. Equipment
mounted on or behind a switchboard panel shall be of the self-contained type or
be installed in a metal or approved enclosure and require the use of a tool or key
to expose live parts. Any work to expose live parts must be undertaken by a
technically competent and skilled person exercising appropriate safety procedures
to avoid contact with live parts.
•
In accordance with the Regulations for the Electrical and Electronic Equipment
of Ships under the Western Australian Marine Act 1982 and Regulations, lighting
circuits should be supplied by final sub-circuits separate from those for heating
and for power requirements. The Australian Standard 3000 - 1991 Wiring Rules
also requires a similar standard to ensure unplanned imbalance of power does not
occur.
13.2 Electric Shock working in ceiling space
This is a summary of an electric shock case investigated by the author
13.2.1 The Incident
An electrician was employed to add a new light switch to an existing installation in a
small parade of shops with office suites over the top. Each shop had a light and a
power circuit but these were controlled from a remote main-switchboard on the first
floor of the office area. Access to the offices was by a doorway fronting the main
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street and a flight of stairs. The front door was locked at weekends. The shops had
wooden floors.
In order to install the new light and switch, the electrician decided to loop an active
conductor from an existing light switch, pull the active wire up the cavity wall using
the existing cable as a draw wire and then take the new circuit through a ceiling space
to the location of the light fitting.
As it was summer time, the electrician was wearing shorts, thongs and a singlet.
He elected to do the work on a Sunday when his wife, who ran a small clothing shop
in the parade was sorting out her stock.
There was no access to the office area and so he was unable to isolate the lighting
circuit at the main switchboard. The circuit that he was going to connect into was a
two way light circuit. He
•
removed the switch cover and disconnected the incoming active,
•
bared the end of a new earth wire and twisted it together with the bare end of the
active,
•
climbed a metal ladder into the ceiling space,
•
lay across the beams and over a metal air-conditioning duct,
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•
started to pull the active wire with earth cable attached into the ceiling space,
•
received an electric shock as soon as he reached the bare twisted wire ends.
It was some time before his wife heard his groans. She had to get her farther, who
had training as a linesman with Telecom, to come and remove her husband (this was
achieved by putting a rubber mat on the ladder and pulling his legs clear of the airconditioning duct). It was some 40 minutes after the initial shock before he was
cleared. During that time he received repeated shocks every time he moved.
The electrician lost several fingers, had recurring bouts of dizziness and head-aches.
He was subsequently not able to resume his trade and had to take a less skilled job.
In a subsequent court action the electrician claimed he had tested the active circuit he
was using as a draw wire and had been misled by the instrument – it had indicted the
circuit was dead when it was in fact alive.
13.2.2 Analysis of Incident
The incident occurred because the electrician broke the following safety rules:1. Improper clothing – full sleeve length cotton shirt and full length trousers are to
be worn when working on electrical equipment.
2. Working on potentially live equipment without an assistant – had a trained
assistant been present he would have been pulled clear within a few minutes and
suffered a lot less trauma.
3. Using an inappropriate test instrument
4. Failure to verify operation of the test instrument on a known live circuit before
use
5. Failure to isolate the circuit before working on it.
6. Failure to insulate himself from earth when working on a potentially live circuit.
Subsequent testing of the light switch and subject test instrument showed it worked
perfectly some 6 months after the event and registered a strong electric field all
around the subject switch.
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The claims regarding the test instrument (it was not a Voltmeter but a battery
powered neon light device that capacitively couples to an electric field) misleading
the electrician where most likely a construct in order to claim damages from the
manufacturer because my testing showed quite clearly that the subject instrument
would register a strong electric field all round the existing light switch from which
the electrician took the active.
When he first removed the active and connected one end of a new earth wire to it (to
form a draw wire) he would have touched the bare conductor with his hand(s). He
received no shock at that time (and it would have been much better if he had –
explain why) because he was wearing thongs and standing on a wooden floor both of
which insulate the body from the return circuit via earth. However when trying to
maneuver in the confined ceiling space he had his bare leg against the metal covering
of flexible air-conditioning ductwork. This provided a moderate resistance path to
earth. Had it been a sheet metal duct he would most likely have been electrocuted4 .
13.3 Death by electric shock and falling
This is a summary of an electric shock case investigated by the author
13.3.1 The Incident
A fourth year electrician apprentice was killed by falling off a metal ladder when he
received an electric shock whilst cutting a cable.
13.3.2 Analysis of Incident
The apprentice was supposed to be pulling a cable along an extensive cable tray
about 2.5m above a concrete floor on a building site. He and his supervising
electrician had been doing similar work earlier that day. The electrician was also
acting as site foreman for a small team of electricians. He needed to attend to some
paperwork and gave instructions to the apprentice to lay new cables onto an over
head ladder tray.
4
electrocution – death by / as a result of electric shock
Prepared by Dr K A Walshe
email : [email protected]
POWER ELECTRONICS 4TH YEAR ELECTIVE.
ELECTRICAL SAFETY; REV A
PAGE 0 - 20
It appears that the apprentice decided to do more than he had been instructed and
proceeded to prepare a cable end to turn into a junction box. He cut a live cable on
the same tray instead of the new cable that he had just pulled into position. He was
using side cutters with insulated handles but subsequently other electricians gave
evidence that the apprentice had a bad habit of keeping his index finger straight
resulting in it touching the bare steel close to the cutting head. Because he was
working from a ladder he would have been holding the frame of the ladder or the
cable tray with one hand.
When he cut the live cable he received a hand – to – hand shock and fell from the
ladder. He died of the injuries received from the fall.
This death was avoidable by:1. Supervisors insisting on and enforcing safe work practices,
2. Using fiberglass or wooden ladders,
3. The apprentice doing exactly as he had been told, and
4. Testing every circuit before working on it
14 Reference List
AS3000 - 2000– “The Wiring Rules” this document has the force of Law in all States and Territories of Australia.
It is now jointly published with the New Zealand Standards Association. Similar Standards exist in most other
parts of the world.
For the effect of lightning see the extensive bibliography “ALPHABETICAL BIBLIOGRAPHY ON MEDICAL
EFFECTS OF LIGHTNING STRIKES” published on the internet by ;R. Holle National Severe Storms
Laboratory, NOAA, 1313 Halley Circle, Norman, Oklahoma.
WorkCover NSW – various pamphlets inc. “Stay Alive Work Dead”
Prepared by Dr K A Walshe
email : [email protected]
WORKSAFE WESTERN AUSTRALIA COMMISSION
ELECTRICITY: RESIDUAL CURRENT
DEVICES
Guidance Note
Occupational Safety and Health Regulations 1996
Regulation 3.60 Protection against earth leakage current
when portable equipment in use
March 1998
SUMMARY
1.
Regulation 3.60 applies to the use of portable electrical equipment used in all
workplaces, other than construction sites. Electrical equipment used on construction
sites is covered by regulation 3.61.
2.
Regulation 3.60 requires the users of portable electrical equipment at workplaces to
be protected against earth leakage current by means of a residual current device
(RCD).
3.
Persons having control of the workplace are required to install non-portable type
RCDs. They have the choice of installing the RCD at the switchboard or in a fixed
socket outlet.
4.
It must be readily apparent to the users of portable electrical equipment if and where
non-portable RCDs have been installed.
5.
If it is not readily apparent or the user is uncertain whether an RCD has been
installed, a portable RCD must be provided by the employer and must be used by the
employee.
6.
This guidance note is issued by the WorkSafe Western Australia Commission to
provide information and advice on the duties of employers, employees, self-employed
persons and persons having control of workplaces under the Occupational Safety
and Health Act 1984 in relation to the use of portable electrical equipment and
meeting the requirements of regulation 3.60 of the Occupational Safety and Health
Regulations 1996.
1.
INTRODUCTION
Electricity is a common workplace hazard, and is a frequent cause of electric
shocks. Some of these shocks have been fatal.
Electricity does not have to be high voltage for an electrocution to occur.
Electrocutions have resulted from contact with faulty electrical equipment that
has become live, or contact with worn and damaged wiring and switches.
While there are many different causes of electrocution, all have one thing in
common – they could be prevented.
In 1992 Worksafe Australia found that of 95 workplace deaths due to
electricity recorded in a work-related fatalities study, 36 deaths – or more than
half of those not caused by aerial powerlines – would probably have been
prevented by the use of RCDs.
The Worksafe Australia study recommended, among other strategies, the use
of RCDs in homes and workplaces. This approach was endorsed by the
WorkSafe Western Australia Commission. Specific requirements for RCDs to
protect users or operators of portable electrical equipment were included in the
Occupational Safety and Health Regulations 1996.
This guidance note was developed within the tripartite WorkSafe Western
Australia Commission, with input from representatives of employer
organisations, trade unions and Government. It is published by the WorkSafe
Western Australia Commission to provide detailed information to assist
employers, self-employed persons, persons having control of workplaces and
employees, in meeting their duties under the Occupational Safety and Health
Act 1984 and the requirements of regulation 3.60 Protection against earth
leakage current when portable equipment in use.
2.
LEGISLATION REQUIRING RCDs
The Occupational Safety and Health Regulations include specific requirements to
protect users or operators of portable electrical equipment. Regulation
3.60 Protection against earth leakage current when portable equipment in use
is designed to minimise the risk of a person receiving a harmful or fatal electric
shock when using portable electrical equipment. Regulation 3.60 does not
apply to construction or demolition sites.
Regulation 3.61 Electrical installations on construction sites requires
electrical installations on construction sites to comply with Australian and New
Zealand Standard AS/NZS 3012 Electrical installations – Construction and
demolition sites. AS/NZS 3012 covers the provision of RCDs on construction
and demolition sites.
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 1
Protection against earth leakage current when portable equipment in use
Regulation 3.60 states
(1)
This regulation applies to a workplace other than one to which AS/NZS 3012 applies
but does not apply to a workplace at which the supply of electricity —
(a)
does not exceed 32 volts alternating current;
(b)
is direct current;
(c)
is provided through an isolating transformer complying with AS/NZS 3108; or
(d)
is provided from the unearthed outlet of a portable generator.
(2) In this regulation —
“hand-held equipment” means portable equipment —
(a)
of a kind that is intended to be held in the hand during normal use; and
(b)
the motor, if any, of which forms an integral part of the equipment;
“portable equipment” means equipment that is —
(a)
connected to an electricity supply; and
(b)
intended to be moved when it is in use,
and includes, but is not limited to, hand-held equipment;
“workplace” means a workplace to which this regulation applies.
(3) A person having control of a workplace —
(a)
must ensure that each non-portable residual current device installed at the
workplace is kept in a safe working condition and tested on a regular basis to
ensure its continued effective operation;
(b)
must provide, where electricity is supplied to portable equipment through a
fixed socket at the workplace after 31 March 1998, protection against earth
leakage current by means of —
(i)
a non-portable residual current device installed at the switchboard; or
(ii)
by a non-portable residual current device built into a fixed socket
which, having regard to the primary use of the socket and its location,
is likely to be used by a person operating portable equipment; and
(c)
must ensure where a non-portable residual current device has been —
(i)
installed at a switchboard, that a notice is displayed in a prominent
place at or near the switchboard indicating that a non-portable residual
current device has been installed at the switchboard; or
(ii)
built into a fixed socket, that the socket can be identified as providing
protection against earth leakage current.
Penalty: $25 000.
(4) A person who is an employer or a self-employed person at a workplace —
(a)
must ensure that each portable residual current device used at the workplace
by the person or an employee of the person is kept in a safe working condition
and tested on a regular basis to ensure its continued effective operation; and
(b)
where the employer or a self-employed person is not satisfied that protection
against earth leakage current has been provided by means of a non-portable
residual current device —
(i)
must provide a portable residual current device for use with each item
of portable equipment used by the person or an employee of the person
at the workplace after 31 March 1998; and
(ii)
must ensure that a portable residual current device is directly
connected to the output side of a fixed socket when an item of portable
equipment is being used by the person or an employee of the person at
the workplace after 31 March 1998.
Penalty: $25 000.
PAGE: 2
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
(5) An employee who is provided with a portable residual current device for use with an
item of portable equipment at a workplace must not use the portable equipment unless the
portable residual current device is directly connected to the output side of a fixed socket.
Penalty: $5 000.
3.
DUTIES OF A PERSON HAVING CONTROL OF A WORKPLACE
Section 22 of the Occupational Safety and Health Act requires a person who
has, to any extent, control of a workplace to ensure, so far as is practicable,
that people who are at the workplace are not exposed to hazards. In many
cases employers will have control over their premises thus having duties under
sections 19, 21 and 22 of the Act. Persons having control of a workplace
include owners, lessors, etc. of premises, who may have no involvement with
the work activity at the premises, but who have retained some control over the
premises. For more information on the general duties of persons at the
workplace see the WorkSafe Western Australia Commission Guidance Note
General Duty of Care in Western Australian Workplaces.
Regulation 3.60 requires a person having control of a workplace to provide
protection for the users or operators of portable electrical equipment against earth
leakage current by means of a non-portable RCD.
The owner or the person managing a building on behalf of the owner, has the
choice of installing non-portable RCDs at the switchboard to protect all or selected
circuits only, or at fixed socket outlets. If the installation is at the switchboard, all
the wiring and appliances plugged into the circuit will be protected. The size of the
building, its use or any plans to refurbish, refit or rewire the building will influence
whether to install RCDs at the switchboard for complete or selected circuit
protection or at fixed socket outlets.
If an owner or manager chooses to have inbuilt RCDs in fixed sockets, not every
fixed socket has to be RCD protected. In deciding which fixed sockets are to have
inbuilt RCD protection, the likely use of the fixed socket has to be taken into
consideration. For example, conveniently located fixed sockets are the most likely
to be used by cleaners or maintenance personnel and should be protected with nonportable RCDs.
Cleaners and maintenance personnel may use up to 30 metres of extension cord or
flexible supply cord between an RCD protected fixed socket and portable
equipment. This distance of 30 metres may be used to assist in determining the
number and location of RCD protected fixed socket outlets to provide coverage for
cleaners.
RCD protection at the switchboard must be identified by a notice displayed near the
switchboard. Where this protection is for selected circuits only, the socket outlets
so protected must each be identified by a notice displayed at the socket outlet.
Where RCD protection has been built into a fixed socket, the fixed socket must be
identified as providing RCD protection.
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 3
4.
DUTIES OF AN EMPLOYER
Section 19 of the Occupational Safety and Health Act requires an employer to
provide, so far as is practicable, a workplace where employees are not exposed to
hazards and to provide a safe system of work. In the case of using portable
electrical equipment the employer should establish whether the fixed socket outlets
to be used by his or her employees are protected by RCDs and whether they are
identified as being protected.
The employer must inform the employees if and where protection is provided. If
the employer is not satisfied that non-portable RCDs have been installed, the
employer should provide a portable RCD and consult with the employee on when
and where the portable RCD is to be used. If there is any doubt regarding the
installation of RCDs at the workplace, portable RCDs must be provided and used.
The use of a portable RCD in a circuit already protected by a non-portable (or
portable) RCD has no detrimental effect on the operation of either RCD.
5.
DUTIES OF EMPLOYEES
Under section 20 of the Occupational Safety and Health Act, employees have a
duty to take reasonable care of their own safety and avoid harming the safety or
health of other people. Before connecting portable electrical equipment to an
electrical power source, an employee should seek the advice of the employer as to
whether the outlets are protected by non-portable RCDs. Where neither the
employer nor an employee is satisfied that non-portable RCDs have been installed,
the employer must provide a portable RCD. The employer and the employee
should consult on when and where the portable RCD is to be used.
6.
WHAT IS A RESIDUAL CURRENT DEVICE [RCD]
RCDs are often known by other names, eg., earth leakage circuit breakers
(ELCB) or safety switches.
An RCD is an electrical safety device specially designed to immediately switch
the electricity off when electricity “leaking” to earth is detected at a level
harmful to a person using electrical equipment. An RCD offers a high level of
personal protection from electric shock. Fuses or overcurrent circuit breakers
do not offer the same level of personal protection against faults involving
current flow to earth.
Circuit breakers and fuses provide equipment and installation protection and
operate only in response to an electrical overload or short circuit. Short circuit
current flow to earth via an installation’s earthing system causes the circuit
breaker to trip, or fuse to blow, disconnecting the electricity from the faulty
circuit.
PAGE: 4
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
However, if the electrical resistance in the earth fault current path is too high to
allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow
to earth for an extended time. RCDs (with or without an overcurrent device)
detect a very much lower level of electricity flowing to earth and immediately
switch the electricity off.
RCDs have another important advantage - they reduce the risk of fire by
detecting electrical leakage to earth in electrical wiring and accessories. This is
particularly significant in older installations.
Residual Current Device (RCD)
Fuses
Circuit Breakers
RCDs work on the principle “What goes in must come out”. They operate by
continuously comparing the current flow in both the Active (supply) and
Neutral (return) conductors of an electrical circuit.
If the current flow becomes sufficiently unbalanced, some of the current in the
Active conductor is not returning through the Neutral conductor and is leaking
to earth.
RCDs are designed to operate within 10 to 50 milliseconds and to disconnect
the electricity supply when they sense harmful leakage, typically 30 milliamps.
The sensitivity and speed of disconnection are such that any earth leakage will
be detected and automatically switched off before it can cause injury or
damage. Analyses of electrical accidents show the greatest risk of electric
shock results from contact between live parts and earth.
Contact with live parts may occur by touching:
*
*
*
bare conductors;
internal parts of an appliance; or
external parts of an appliance that have become “live” because of an
internal fault.
Contact with earth occurs through normal body contact with the ground or
earthed metal parts.
An RCD will significantly reduce the risk of electric shock, however, an RCD
will not protect against all instances of electric shock. If a person comes into
contact with both the Active and Neutral conductors while handling faulty
plugs or appliances causing electric current to flow through the person’s body,
this contact will not be detected by the RCD unless there is also a current flow
to earth.
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 5
On a circuit protected by an RCD, if a fault causes electricity to flow from the
Active conductor to earth through a person’s body, the RCD will automatically
disconnect the electricity supply, avoiding the risk of a potentially fatal shock.
Fault current path/s to earth
7.
TYPES OF RCDs
There are three types of RCDs – switchboard mounted, powerpoint (GPO)
type and plug in (portable). Switchboard mounted and powerpoint types are
referred to as non-portable RCDs. Portable RCDs are plugged into a fixed
socket. A non-portable RCD installed at the switchboard is the best option in
most situations as it protects all the wiring and appliances plugged into the
circuit, however, the regulation provides the option of providing non-portable
RCDs built into fixed sockets.
Switchboard Units
These are non-portable units installed at the switchboard to provide protection
of the complete installation, or protection of a selected circuit.
Switchboard RCD units.
These may be installed at the
main switchboard to provide
complete installation protection
or selected circuit protection
PAGE: 6
RCD installed at the switchboard
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
Fixed Socket Units
These are non-portable units consisting of RCD protection inbuilt into a fixed
socket outlet to provide protection to equipment plugged into the outlet.
RCDs incorporated in fixed sockets
provide single outlet or single
circuit protection. This type of unit
may be installed at selected
locations instead of providing
protection at the switchboard
RCD incorporated in fixed socket
Portable Units
These are to be used where doubt exists that non-portable RCD protection has
been provided. Various models are available from simple plug adaptors to
units designed for specific equipment such as the portable unit shown below or
wired, by a licensed electrical worker, to an extension cord.
Portable RCD unit suitable for use with
extension cords and portable power tools
Portable RCD
plug adaptor
Plug adaptor wired
to an extension cord
Portable RCD plugged into external power point
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 7
8.
SUPPLY OF ELECTRICITY WHERE REGULATION 3.60
DOES NOT APPLY
Regulation 3.60 states that the requirements of the regulation do not apply in
the following situations:
q Workplaces where AS/NZS 3012 applies
AS/NZS 3012 Electrical installations – Construction and demolition sites,
specifies requirements for electrical installations which supply electricity to
appliances and equipment on construction and demolition sites, and for the
in-service testing of portable, transportable and fixed electrical equipment
used on construction and demolition sites.
Regulation 3.61 Electrical installation on construction sites mandates
AS/NZS 3012. The requirements for RCD protection on construction sites
has been carried forward from the repealed Occupational Health, Safety
and Welfare Regulations 1988.
q Where the supply of electricity does not exceed 32 volts alternating current
(AC) or is direct current (DC)
The severity of an electric shock depends upon the following factors:
- the magnitude and path of the current through the body;
- the duration of the shock; and
- the type of voltage supply, AC or DC.
Alternating currents are much more likely to cause serious shocks than
direct currents of similar voltages. Alternating currents of even low value
exercise a paralysing effect upon the muscles causing the victims grip to
tighten, making self release difficult or impossible.
Most people will not be adversely affected at 32 volts AC. Alternating
current of such low voltage is usually sourced independent of supply mains,
or from the supply mains through an isolating transformer.
Electrocution from DC current is far less likely than with AC current
because with DC current it is easier to remove the grip on live parts and
because DC current has a lesser effect on the cardiac system. Direct
current, however, should always be treated with care.
q Where supply of electricity is provided through an isolating transformer
complying with AS/NZS 3108 or from the unearthed outlet of a portable
generator
An isolating transformer is a transformer designed to supply extra low
voltage and low voltage circuits, the input windings being double insulated
(or equivalent insulation) from the output windings. Advice from a person
competent in electrical installations should be sought regarding the need, or
otherwise, for RCD protection of portable equipment supplied from
portable generators or through transformers.
PAGE: 8
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
9.
INSTALLING AND PROVIDING RCDs
The person having control of the workplace, eg., the owner of the property, or the
person managing the property on behalf of the owner has a responsibility to provide
non-portable RCD protection at the switchboard to protect all or selected circuits
only, or in a reasonable number of fixed socket outlets in each section or area of the
workplace where portable electrical equipment is in regular use. These outlets
must be clearly identified.
If it is not readily apparent that non-portable RCDs have been installed at a fixed
socket or at the switchboard, the employer of persons using portable electrical
equipment must ensure the portable electrical equipment used by their employees is
protected by a portable RCD unit which is directly connected to the output side of
a fixed socket. The various types of portable RCDs are shown at Section 7.
Directly connected means there is no extension cord connecting the portable RCD
to the output side of the socket or in the case of a portable RCD with a flexible
supply cord, no extension cord is used to connect the RCD to the socket. As the
flexible supply cord is not RCD protected, its length should be as short as possible
and must not be increased beyond that supplied or specified by the manufacturer.
No additional extension cord is to be used to connect the RCD to the socket as this
would increase the length of unprotected cord.
Non-portable RCDs must be installed by a licensed electrician or licensed
electrical in-house worker. Only a correctly installed RCD will provide the
required level of personal protection. It is a requirement of the Electricity Act
1945 and Regulations that the installation must comply with
AS 3000 Electrical installations – Buildings, structures and premises (known
as the SAA Wiring Rules).
Portable electrical equipment that is known to be damaged or faulty must not
be used until repaired by a licensed electrical worker.
10.
EQUIPMENT REQUIRING RCD PROTECTION IN ACCORDANCE
WITH REGULATION 3.60
“Portable equipment” is defined as equipment that is —
(a)
(b)
connected to an electricity supply; and
intended to be moved when it is in use,
and includes, but is not limited to, hand-held equipment.
“Hand-held equipment” is defined as portable equipment —
(a)
(b)
of a kind that is intended to be held in the hand during normal use; and
the motor, if any, of which forms an integral part of the equipment.
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 9
Portable electrical equipment that requires protection includes, but is not
limited to, the following items which are intended to be moved whilst in use:
*
*
*
*
*
hand-held power tools such as drills, saws, planers, grinders and
chainsaws;
power equipment such as jack-hammers and lawn mowers;
cleaning equipment such as vacuum cleaners and industrial polishers;
hand-held appliances such as hair dryers and curling wands; and
cord extension leads connected to any of the above items (ie., portable
RCDs must also protect the cord extension lead).
The above items of portable equipment may be single phase or three phase.
RCD protection to some types of portable equipment will depend on the
situation in which the equipment is used. For example, in the entertainment
industry, if any part of a sound system such as a microphone, is intended to be
held in the hand or moved when in use, that part of the system should be
protected by an RCD if it is powered by alternating current exceeding 32 volts.
Similarly, portable or stage lighting exceeding 32 volts which is hand held or
intended to be moved when in use should be RCD protected.
RCD protection is not required if power is supplied through an isolating
transformer complying with AS/NZS 3108.
Appliances which are “double insulated” (clearly marked with the words
“Double Insulated”, or with the double square symbol o ) provide additional
protection against electrocution because of their construction. They protect
the user from receiving an electric shock from the casing of the equipment.
However, the flexible supply cord attached to the appliance or a cord extension
lead used is a potential source of electrocution and requires RCD protection.
11.
EQUIPMENT TO WHICH REGULATION 3.60 DOES NOT APPLY
Electrical equipment that presents a very low risk includes, but is not limited to:
*
*
*
*
*
*
desk top computers, computer printers and monitors;
photocopiers;
refrigerators;
television sets and VCRs;
equipment connected by fixed wiring; and
large stationary equipment connected by a flexible cord which is not
flexed during normal use, for example, a window-mounted air
conditioner.
RCDs are not suitable for providing protection from electric shock from the
handpiece of welding equipment. It is not feasible to provide RCD protection
to the welding handpiece since current leaking to earth in the circuit between
the electrode conductor and the return conductor will continually trip out an
RCD.
PAGE: 10
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
However, the primary winding of the power source of the welding plant will
require RCD protection if the welding plant is portable equipment intended to
be moved while in use. Portable RCD protection must be provided to any
portable or hand held electrical equipment which is supplied with electricity
from a power outlet on welding equipment, unless the power outlet has inbuilt
RCD protection.
AS 1674 Safety in welding and allied processes Part 2: Electrical provides
information on preventing electric shock in welding operations through sensible
preventative measures involving inspection and maintenance of equipment, safe
operating procedures and safety precautions.
Medical equipment, where a “trip out” could be detrimental to a patient, should
not be RCD protected.
All portable electrical equipment should be regularly checked and tested in the
workplace by a competent person.
12.
RISK ASSESSMENT OF OTHER EQUIPMENT
Electrical equipment that is not moved or carried while being operated presents
a very low risk of electric shock and while it is not required to be protected by
RCDs under the provisions of regulation 3.60, the equipment should be
assessed in accordance with regulation 3.1.
Identification of hazards, and assessing and addressing risks, at workplaces
Regulation 3.1 states
A person who, at a workplace, is an employer, the main contractor, a self-employed
person, a person having control of the workplace or a person having control of access
to the workplace must, as far as practicable —
(a) identify each hazard to which a person at the workplace is likely to be
exposed;
(b) assess the risk of injury or harm to a person resulting from each hazard,
if any, identified under paragraph (a); and
(c) consider the means by which the risk may be reduced.
Penalty:$25 000.
Where an assessment under regulation 3.1 indicates a person using electrical
equipment is at risk of receiving an electric shock, the use of an RCD should be
considered, and if appropriate, used as a means of reducing the risk. It is
highly probable the assessment will indicate electrical appliances and equipment
likely to be used in a wet or hazardous environment may need to be protected.
In some situations these could include washing machines, kettles, frypans, jugs
and ice making machines. The presence of moisture will increase the risk
associated with the use of electrical equipment.
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 11
13.
INSPECTION AND TESTING
Guidelines for inspection and testing of portable RCDs are provided in
AS 3760 In-service safety inspection and testing of electrical equipment.
AS 3760 sets out, in table 1, the intervals between push button testing (by user)
and inspection testing for operation by an electrician for various types of
environments in which portable RCDs are used.
The information in AS 3760, table 1, is set out below.
Type of environment
in which equipment
is used
Interval between inspection and tests for
portable RCDs
Test for operation
Push-button test (by
(by
licensed electrical
user)
worker)
Factories, workshops and
places of work of
manufacturing, repair,
assembly, maintenance or
fabrication
Daily, or before every
use, whichever is the
longer
Other commercial
environments with no
special protection, eg.,
laboratories, tea rooms,
office kitchens, and health
care establishments
3 months, or before
2 years
every use, whichever is
the longer
12 months
Office environment where 3 months
equipment is not subject to
constant flexing of the
supply cord
2 years
Hire equipment
Before each hire
Before each hire
Testing of non-portable RCDs at switchboards or inbuilt into socket outlets
must be carried out on a regular basis. This includes both push button testing
by the user and inspection testing for operation by a licensed electrical worker.
Unless operated from time to time, an RCD may “mechanically freeze” and not
trip when required.
Push-button testing by the user only confirms satisfactory mechanical
performance of the tripping mechanism of the RCD. It does not replace
inspection testing for operation by a licensed electrical worker.
PAGE: 12
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
As non-portable RCDs are far less susceptible to damage than portable RCDs, they
are not subjected to the same testing and inspection procedures. In the case of
non-portable RCDs, push button testing is recommended at three monthly intervals.
After tripping out, an RCD must be re-activated in accordance with a
"re-establishment of supply" procedure which requires the cause of the trip to
be established and remedial action taken before re-establishing the supply.
These procedures should be drawn up by the employer after consultation with
employees and safety and health representatives, if any.
GUIDANCE NOTE –ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
PAGE: 13
OTHER PUBLICATIONS
The following publications can be purchased from WorkSafe Western Australia,
Westcentre, 1260 Hay Street, West Perth [Tel. (08) 9327 8777]:
q Occupational Safety and Health Act 1984;
q Occupational Safety and Health Regulations 1996;
q Codes of Practice published by the WorkSafe Western Australia Commission:
*
*
*
*
*
*
*
Excavation;
First Aid, Workplace Amenities and Personal Protective Equipment;
Legionnaires Disease;
Manual Handling;
Management of HIV/AIDS, Hepatitis B & C at Workplaces;
Prevention of Falls at Workplaces; and
Styrene.
q Guidance Notes published by the WorkSafe Western Australia Commission:
*
The General Duty of Care in Western Australian Workplaces; and
*
Election of Safety and Health Representatives, Representatives
and Committees and Resolution of Issues.
These documents are also available via the Internet Service on Safetyline
[http://www.safetyline.wa.gov.au].
The following publications are under development or are expected to commence
development during 1997/98 and when available will be listed in “What’s New” on the
Internet Service:
q Codes of Practice:
*
*
*
*
*
*
*
*
Abrasive Blasting;
Control of Noise in the Music Entertainment Industry (Review);
Demolition;
Isocyanates;
Legionnaires Disease (Review)
Spraypainting;
Steelwork;
Young Workers;
q Guidance Notes:
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PAGE: 14
Competent Persons;
Powered mobile plant;
Communication with isolated employees;
Registration of plant design;
Registration of individual items of plant.
GUIDANCE NOTE – ELECTRICITY: RESIDUAL CURRENT DEVICES
30 MARCH 1998
S E L E C T I O N O F U S N AV Y
E L E C T R I C A L AC C I D E N T R E P O RTS
The following pages are accident report sheets from the US Navy
Naval Facilities Engineering Command
Abstract of an Accident
FY95-5
MISHAP TYPE:
INJURY:
DAMAGE:
TYPE OF WORK:
EQUIPMENT:
Explosion (Electrical)
None
Est. 50K - 100K
Drilling (Environmental Site)
Drilling Rig
DESCRIPTION OF MISHAP
An electrical explosion occurred on a BRAC Closure Site during the course of the Phase II
Environmental Baseline Survey field effort being conducted by a drilling subcontractor. The
subcontractor had obtained site plans showing utility locations, and conducted a site walk-through
before selecting soil boring locations. Six days later the drilling rig was set up to begin taking soil
samples. Drilling proceeded with caution, as the subcontractor was aware of underground utilities in
the area. A hand auger was advanced to 3.5 ft at which point hand auguring was not possible due to
the coarse gravel. At this point the 4.25 inch ID hollow stem auger was advanced to a depth of
approximately 5 ft. The drillers were about to add another flight of augers. As the auger was slowing to
a stop the workers heard a “hissing sound” coming from the hole. Within seconds flames erupted and
the workers fled the area. Smoke was subsequently observed coming from two adjacent buildings and
from a manhole near the site. The drilling rig was engulfed in flames.
DIRECT CAUSE
Subcontractor drilled through an electrical high voltage cable supplying power to a building from
transformer station.
INDIRECT CAUSE
- Inadequate identification of underground utility lines.
- Use of the 4.25 inch ID hollow stem auger.
LESSONS LEARNED
Contractors must ensure they identify all existing utilities prior to beginning work. They must not only
acquire utility maps but also use the maps and site plans and carefully survey the area to identify
problem areas before selecting drilling sites. If there are underground utilities in the immediate area
then hand auguring or excavation must be accomplished to avoid mishaps.
YOUR SAFETY CONTACT IS....
Naval Facilities Engineering Command
Abstract of an Accident
FY95-7
MISHAP TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Electrocution
Fatality
Splicing High Voltage Overhead Line
Bucket Truck
DESCRIPTION OF MISHAP
A High Voltage Electrician was electrocuted by 4160 Volts when he contacted an energized overhead
power line with his bare hands. The fatality occurred when a two-man crew, consisting of the
electrician and a helper (also an electrician), attempted to permanently repair a temporarily spliced
overhead power line. The electrician and his assistant had cut the power to the line from a nearby
transformer; however, the lines were being fed from a different location. Thinking the power to the line
was off; they began repairing the line. Working from an elevated bucket, the electrician initially worked
while wearing his insulated gloves, but later removed them to rejoin the line into a crimp sleeve for the
final phase of the repair. With his bare hands, he grasped the two ends of the energized 4160 volt line
and was immediately electrocuted. The assistant, working in the bucket next to him, lowered the
bucket and summoned emergency personnel, but the electrician died within minutes.
DIRECT CAUSE
Failure to follow standard Lockout/Tagout/Tryout/Groundout procedures
INDIRECT CAUSES
No SOP for operation, inadequate supervision, inadequate LO/TO program oversight, inadequate
employee development/certification.
LESSONS LEARNED
Jobs involving lethal voltages should not be considered routine. No SOPs based on JHAs were
completed on this job because it was considered a routine, low-risk job. Larger jobs received full written
guidance.
Supervision must treat all jobs involving electricity with the respect it warrants not just large jobs. The
supervisor rarely visited jobs in progress or small-scale jobs like this one, but routinely visited larger
jobs.
Evaluation and enforcement of LO/TO program requirements is critical to implementing this program
throughout an activity. The evaluation of the activity’s program did not involve reviewing employee’s
performance applying the program in the field. Supervisors did not routinely enforce the requirements.
Employees did not receive specialized training critical to their trade sufficient to work in a safe manner.
Generally, employees are hired in at a skill level, there is no system to improve/certify employee skills.
YOUR SAFETY CONTACT IS....
Naval Facilities Engineering Command
Abstract of an Accident
96-3
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Electrocution
Fatality
Electrical Substation
34.5 KV Overhead Switch
DESCRIPTION OF THE ACCIDENT:
A contractor worker was installing a high voltage cable support bracket onto the main switch support
column of an electrical substation. His supervisor held the bracket in place while the worker stood on a
fiberglass ladder next to an energized 34.5KV buss and bolted the bracket in place. During this
operation, the worker reached out with his right hand and touched an insulator of the 34.5KV buss and
was shocked. High voltage electricity entered his right hand, traveled through his body and exited from
multiple locations causing burns to his face, hands, waist, upper back, and internal organs. He
collapsed and fell from the ladder, later dying from his injuries.
DIRECT CAUSE:
Work was performed adjacent to a 34.5KV electrical circuit without the required safe clearance, without
securing the electrical circuit and not using high voltage electrical PPE. The injured worker was a
laborer and not qualified to work on or near high voltage electricity.
CONTRIBUTING CAUSES:
•
•
•
Activity Hazard Analysis was not being applied by the contractor's site superintendent
Weekly on-site safety training was not conducted
Site specific safety training was not conducted prior to this phase of work
LESSONS LEARNED:
•
•
•
•
Always request an electrical outage when work is required to be accomplished on or near high
voltage circuits.
Contractor safety plan implementation to be site specific is critically important.
Phase hazardous analysis could have prevented this mishap by not allowing work to be performed
by unqualified workers and properly identifying the hazards associated with this work area.
Worker safety awareness is essential in preventing accidents by using only qualified workers and
preventing unsafe conditions.
Naval Facilities Engineering Command
Naval Facilities Engineering Command
Abstract of an Accident
97-3
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Near - Electrocution
Potential Fatality
Excavation (Digging Foundation with Jack Hammer)
12 KV Concrete Ductbank
DESCRIPTION OF THE ACCIDENT:
A Navy civilian worker was chipping concrete with a jack hammer from what he mistakenly thought was
a building foundation, but was actually a high voltage ductbank, when the tip penetrated the concrete
and contacted a 12,000 Volt (12KV) conductor inside. Although the resulting significant electrical short
and arc-blast did not injure the employee, the jack hammer was damaged and power to a large area of
the facility was lost for approximately 12 hours.
DIRECT CAUSE:
Underground utility locator marks, identifying the ductbank before excavating, were removed during the
first stages of the excavation work. No site drawings identifying the underground utilities were available
for reference after locator marks were removed.
CONTRIBUTING CAUSES:
•
•
Although locating and marking of underground utilities is universally required, there is no
requirement that site sketches of the identified utilities be made and maintained for reference during
excavation.
No site specific safety training was conducted prior to digging to acquaint employees with local
utilities and to prepare them for the hazards of digging into live utilities.
LESSONS LEARNED:
•
•
•
•
Establish requirement for site sketches which identify location of underground utilities.
Ensure sketches are retained for reference during excavation work.
Ensure underground utilities, including concrete structures, are not dug/drilled/broken until tested
safe to do so.
Ensure employees are trained on safe digging practices and dangers of digging without identifying
underground utilities.
YOUR SAFETY CONTACT IS....
Naval Facilities Engineering Command
Abstract of an Accident
98-10
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Near Miss Electrocution
N/A
High Voltage Electrical
Hand Operated Cable Cutter
DESCRIPTION OF THE ACCIDENT:
A certified high voltage cable splicer mistakenly cut an energized high voltage cable in preparation of cable splice
work causing an arc which fortunately did not result in property damage or personnel injury. An electrical system
outage procedure was followed which included an advanced outage coordination meeting with station utilities to
review the work, outage procedures, and contractor hazardous energy control methods. When the cable splicer
entered the underground manhole to perform the work he found that the cables were not identified. He then
contacted the station utility electrician to assist in assuring the proper cable was deenergized. After performing
visual tracing of the cable to be worked on from a nearby manhole, and using two separate electrical test
instruments, both showing that the circuit was not energized, the cable splicer cut the cable. The cable was hot.
The cable arced for 30 minutes until arrival of the utility electrician who isolated the hot circuit.
DIRECT CAUSE:
• The cable splicer failed to adequately identify that the circuit was still hot.
CONTRIBUTING CAUSES:
• There are limits to the ability of electrical test equipment to adequately identify the presence of electrical
energy. This is largely based on the amount of cable insulation (%) for the cable type. The tests were
performed without identifying the energy because the instrument could not test through 133% cable insulation.
• The cable was not cut using a remote non-conductive hydraulic cutter as required in the new 01525-guide
specification. The contract was written prior to the existence of the new guide specification.
• The outage should have been cancelled when it was found that the cables were not identified. Although the
utility electrician came to the site and looked into the manhole he did not perform cable identification for the
contractor.
LESSONS LEARNED:
• Certified high voltage cable splicers must review manufactures instructions of electrical energy detection
equipment to correctly understand equipment limitations. A Process Action Team (PAT) has been organized
and tasked with providing recommendations for test equipment types and procedures. The PAT team is a
cooperation of station utility, safety, and construction professionals. Recommendations will follow.
• Cable identification procedures are being formulated by the PAT, which will be incorporated into 01525-guide
specification. These procedures will include requiring contractor investigation of cable identification prior to
acceptance of any outage request. Additionally, unlabeled cables are to be identified by station utility personnel
prior to the requested outage.
• Cutting of high voltage cable is to be performed remotely. This requirement has been incorporated into the
1997 01525-guide specification. The guide specification requirement should be incorporated into existing
contracts and included in the next version of USACE EM 385-1-1.
YOUR SAFETY CONTACT IS....
Naval Facilities Engineering Command
Abstract of an Accident
98-8
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Electrical Shock
Permanent Partial Disability
High Voltage Electrical
Electrical Distribution Panel
DESCRIPTION OF MISHAP
Employee was shocked by 7,200 Volts AC when electrical power unexpectedly routed through a
transformer he was working on. Employee was part of a crew working on a transformer located in a
substation. The transformer had been de-energized, isolated, and grounded on all legs except one that
consisted of a fused cutout, which was opened, and the fuses left exposed. After making the
transformer “safe”, fellow workers began trouble-shooting auxiliary circuits to turn on power for heaters
and lights within the transformer while other workers did unrelated work. When a circuit on the panel
labeled “auxiliary power” was turned on, the distribution system back-fed electricity to the transformers’
exposed fuses. The employee, standing directly in front of the fuses, was shocked immediately after
actuation of the 120 Volts AC auxiliary circuit. Activating the auxiliary circuit directed power through an
uncharted section of the distribution system to the transformer, which amplified it to 7200 Volts AC and
energized the fuses where the employee was standing unprotected. The electricity entered the
employees’ back and exited through his right hand.
DIRECT CAUSE
•
Failure to follow requirements of lockout/tagout/tryout procedures (1910.147 or .269) – Authorized
person did not ensure all personnel were clear of equipment that might be affected before
introducing a change in the (lockout/tagout/tryout) process.
INDIRECT CAUSES
•
•
System owners did not ensure all circuits were indicated on distribution system drawings/one-line
diagrams when the system was built or modified.
No procedures for ensuring all circuits are identified and verified before treating as safe.
LESSONS LEARNED
•
•
•
Supervisors and employees must fully understand and implement Energy Control Program
requirements, including lockout/tagout/tryout procedures.
Personnel must be protected during all operational phases, including trouble-shooting and
experimental evolutions.
System drawings, including one-line diagrams, must accurately identify all circuits to reflect
system operation and function.
YOUR SAFETY CONTACT IS....
Naval Facilities Engineering Command
Abstract of an Accident
98-9
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
EQUIPMENT:
Electrical Shock
Permanent Disability
Construct REBAR Cages for Concrete Forms
Hardhat, Steel Toe Boots
DESCRIPTION OF ACCIDENT
An employee was shocked by 38,000 Volts AC when a REBAR tie wire he was holding contacted an
overhead high-voltage powerline. Two employees were tasked with constructing REBAR cages for
concrete forms. This required making tie wires for tying and securing REBAR cages in the forms from
continuous lengths of wire on coils. The process of making the tie wires involved pulling out two
strands of tie wire from a coil, straightening and then manually twisting the two strands together, then
cutting the lengths into nine-inch sections. The injured employee was standing on the ground below,
and approximately fourteen feet forward of a 38,000 Volt AC overhead powerline located thirty-six feet
above. The employees were stretching approximately sixty feet of double strand tie wire when it
snapped, recoiled upwards, and contacted the powerline. Electricity traveled down the tie wire, in
through the injured man’s hand, and out his leg.
DIRECT CAUSE
•
Lack of situational awareness and deviating from established procedures.
CONTRIBUTING CAUSES
•
•
The Project Safety Plan did not include electrical shock hazard for tying REBAR.
Job Hazard Risk Analysis for tying REBAR was accomplished for impalement but not for electrical
shock hazard.
LESSONS LEARNED
•
•
•
Standard Operating Procedure (SOP) for tie wire and similar operations should include a check for
electrical hazards.
Each process change should be evaluated - Significant hazards may exist from process changes
although no historical data indicates it (a change in the tie wire preparation process resulted in
serious electrical shock from whipping hazard).
Ensure Operational Risk Management (ORM) is used for any process. Applying ORM will: identify
all potential hazards, assess the hazards to determine severity and probability, develop and
implement risk control options, monitor for change in the process.
YOUR SAFETY CONTACT IS.….
Naval Facilities Engineering Command
Abstract of an Accident
99-03
ACCIDENT TYPE:
INJURY:
TYPE OF WORK:
Electrical Mishap
Shock
Relocating Outdoor Condenser Unit
DESCRIPTION OF ACCIDENT:
While relocating an outdoor condenser unit for a 2-ton split A/C a contractor electrician received an
electric shock when he attempted to cut a live electrical wire. The injured electrician suffered cardiac and
respiratory arrest as a result of the shock. CPR was performed by co-workers, Navy personnel from
nearby spaces and by the base medical department. He was revived and transported to a local hospital
where he spent a week recovering before returning to work.
DIRECT CAUSE:
♦
♦
Lock-out tag-out procedures were not followed properly. The circuit breaker and double pole
switch for the A/C unit is located inside a secure space not readily accessible for contractor
access. The contractor requested that a Navy security escort go inside the secure space and
switch off the double pole isolator switch for the A/C unit. No attempt was made to secure the
breaker (lock-out) or tag either the double-pole switch or the breaker to prevent accidental
energizing of the circuit (tag-out).
The injured electrician was standing on an aluminum stepladder and working in close proximity to
a steel ISO shipping container, both good conductors that may have increased the severity of the
shock he received. No insulating material such as rubber matting was used.
INDIRECT CAUSE:
♦
♦
♦
Inadequate contractor hazardous energy control plan.
Failure to consider restricted access to energy control devices.
Failure to “lock-out” the system and “tag-out”
LESSONS LEARNED:
♦
♦
♦
♦
Contractor’s hazardous energy control procedures must be submitted and accepted by the
ROICC prior to start of work.
Current lock-out tag-out procedures need to be strictly followed by contractors.
ROICC offices should ensure that lock-out tag-out is emphasized in contractor safety meetings
and enforced at the site.
Contractors need to strictly observe the requirement to coordinate power outages with
appropriate base personnel and the ROICC.
YOUR SAFETY CONTACT IS....