Download Fault find general principles

EKAS 2.19.28
Fault find- General Principles
UEE31307 Certificate III in
Refrigeration and Air Conditioning
Stage 2A
Units: UEENEEPOO1B
Chris Hungerford
Saturday, April 29, 2017
The two golden rules
• Test before you touch,
this
protects you physically, so you can have a good day!
• Test your work is electrically
safe when completed, tests include
insulation resistance, earth continuity, polarity, and
visual inspection, this protects you financially.
2.19.28.A
Safe Isolation of a Supply
• Test before you touch, this protects you physically,
so you can have a good day!
1.
2.
3.
4.
5.
6.
7.
2.19.28.A
Procedure to isolate a Supply
Notify all persons likely to be affected by the isolation.
Determine the method to isolating the supply.
Test the supply availability.
Isolate the supply.
Danger tag the isolation device.
Test that the supply is isolated.
Test the testing device.
WARNING
Are you working LIVE?
Using a voltmeter to measure low voltage is working live!
Electrical Safety Regulation 2002
11 Requirements for electrical work
(1) An employer or self-employed person must ensure that, unless
the circumstances required under this division for the performance
of live work apply, live work is not performed.
Maximum penalty—40 penalty units.
As per Regulation 12 “Requirement for performance of live work”, to perform live work you must satisfy the following
seven (7) questions:
1. Have you prepared a risk assessment?
2. Is your test equipment appropriate to perform live work? Minimum Cat III @ 500v ac.
3. Has your test equipment been maintained and confirmed that it is operating correctly? Regulation 18.2(b) “the instrument
4.
5.
6.
7.
is tested at least every 6 mths to ensure it is in proper working order”, and Regulation 12.1(f) “the instrument is tested immediately prior to
work to confirm that the instrument is operating correctly”
Have you the correct PPE, (Safety boots, long pants, long sleeved shirt, insulated gloves, safety glasses)? As per
AS/NZS 4836 Safe working on low voltage electrical installations.
Is the isolation point clearly identified?
Is the isolation point able to be reached without any obstructions?
Is the area where the electrical live work is performed clear of any obstructions?
Note: if you are not working within the requirements of the above laws then your inaction to comply threatens the following;
1.
Your right to claim workcover in the event of an accident
2.
Your right to claim any insurance benefits in the event of an accident
3.
You will be fined the prescribed penalty units for those laws that you have breached.
What is a Fault?
• Any condition in an electrical system that is
dangerous or unsafe is a fault.
• Any condition that will prevent the electrical
system from operating correctly is a fault.
2.19.28.B
Overload An overload is a condition where the
load on the circuit is too much, causing the
current to exceed the current rating of the
cables and supply. If the excessive current was
allowed to continue, the cables would heat
above their rating and may lead to a short
circuit.
6A fuse
Load
48
240v
I = V = 240 =
R
48
2.19.28.B
6A fuse
5A
240v
I = V = 240 =
R
24
10A
Short circuit, A very severe condition and will
cause fire, burns, and equipment damage if not
protected against. The only resistance to the
current is that of the supply cables and the size of
the electrical source.
cables = 0.5
cables = 0.5
Load
47.5
240v, 500A
supply
I = V = 240 =
R (47.5+.5)
240v, 500A
supply
2.19.28.B
short circuit
0.5
240v, 500A
supply
5A
8A fuse
I = V = 240 =
R (.5+.5)
Load
48
240A
short circuit
0.5
The fuse will open circuit when
the current exceeds it’s rating.
Partial open circuit, (hot joint) caused by loose
or dirty connections that causes an increased
circuit resistance. This increased resistance
causes a heating effect at the joint and reduces
the current at the load. Will cause fire and
equipment damage. A fuse or circuit breaker will
not protect against this type of fault. The only
combat is by visual inspections or thermal
imageries.
12
240v
48
I = V = 240 =
R
48
2.19.28.B
P=V*I
=240 *5
= 1200W
5A
240v
P=I 2 R = 42*12 = 192W
48
I = V = 240 =
R (12+48)
2
P=I2 *R =4 *48=768W
4A
Partial short circuit Like a short circuit with a
higher resistance. Normally earth faults. Fuses
and circuit breakers may not open circuit if the
fault current does not exceed their rating. Earth
leakages are good examples.
6A fuse
6A fuse
5A
I = V = 240 =
R
48
2.19.28.B
5A
240v
I=V =
R
48
240v
Load
48
120
2A
240 =
34.2
7A
Procedures for fault finding
Voltage
Present
Not present
Measure
current
No current
High current
Measure
resistance
Low current
Very low
resistance
Measure
resistance
Open
circuit
2.19.28.B
Partial
short circuit or
overload
Partial
open circuit
Short
circuit
Low
resistance
Partial
short circuit or
overload
Flowchart For Problem Resolution
NO
YES
Is It Working?
Don’t Stuff With It!
YES
Did You Stuff
With It?
YOU IDIOT!
NO
Anyone Else
Know?
NO
Hide It
YES
You’re SCREWED!
NO
Can You Blame
Someone Else?
Yes
NO PROBLEM!
YES
Will it Blow Up
In Your Hands?
NO
Look The Other Way
Overvoltage category
Common sense ways to think
of categories
• The higher the short circuit fault
current available, the higher the
category
– High energy transients are much more
dangerous, because they can trigger
an arc blast
• The greater the source impedance,
the lower the category
2.19.28.B
2.19.28.B
What’s the bottom line?
• If you work on power circuits, you
need a CAT III-600 V or CAT IV-600 V/
CAT III 1000 V meter.
• Look for the CAT rating and voltage
rating marked near the input jacks.
– CAT or voltage rating alone can be
misleading
• Look for independent certification.
CAT IV-600 V
CAT III-1000 V
2.19.28.B
Fault finding: Continuity technique
• Warning: Disconnect the supply.
• All healthy component’s circuit have a value of resistance.
• Placing an ohmmeter across the component should indicate the
components condition.
– Values of 0 are considered as short circuited.
– Values of infinite ohms are considered as open circuited.
2.19.28.B
Fault finding: Supply available technique
• Low voltage is present therefore Regulation 12 ESR2002
must be satisfied before working live.
• Voltmeter set to highest scale
• Place voltmeter across the circuit with supply available:
– the voltmeter should indicate the supply if healthy.
– If the voltmeter does not indicate the supply then search across
the circuit devices for the voltage.
T=25deg C
T/O
A 240V
A1
Voltmeter should indicate 240v if healthy
2.19.28.B
contactor
HP/LP
A2
N
T=25deg C
A 240V
T/O
contactor
HP/LP
A1
A2
Voltmeter = 0v
NO supply indicated by the voltmeter, be careful,
•just because the voltmeter does not indicate any voltage does not
mean there is no voltage present, the voltage difference across the
across the HP/LP is zero. It could be 240v each side of the HP/LP
therefore the difference is zero.
2.19.28.B
N
T=25deg C
T/O
contactor
HP/LP
A 240V
A1
Voltmeter = 0v
Voltmeter=0v, the fault has not shown itself.
2.19.28.B
A2
N
T=25deg C
T/O
contactor
HP/LP
A 240V
A1
Voltmeter = 240v
Voltmeter=240v, the fault has shown itself.
A healthy circuit the voltage should be 0v across a closed
switch. This voltmeter indicates a difference therefore the T/O is
defective.
2.19.28.B
A2
N
T=25deg C
A 240V
T/O
contactor
HP/LP
A1
Voltmeter = 180v
2.19.28.B
A2
N
T=25deg C
A 240V
T/O
contactor
HP/LP
A1
Voltmeter = 180v
Voltmeter = 180v, therefore the circuit between HP/LP to A1 is OK.
2.19.28.B
A2
N
T=25deg C
A 240V
T/O
contactor
HP/LP
A1
Voltmeter = 240v
Voltmeter = 240v, and 180v as before, therefore, the problem must
be across the HP/LP.
2.19.28.B
A2
N
T=25deg C
T/O
A 240V
contactor
HP/LP
A1
A2
Voltmeter = 60v
Voltmeter = 180v
The Voltmeter across the HP/LP should be equal to 0v as the
resistance of a closed switch should be as close to zero ohms.
The voltmeter indicates an elevated voltage (60v) therefore there
must be an elevated resistance, i.e. high resistance.
2.19.28.B
N
Work Record required by Regulations
Electrical Safety Regulation 2002
Part 2 Electrical work
14 Testing of electrical equipment after electrical work
(1) This section applies if electrical work is performed on electrical equipment.
(2) A person who performs part or all of the electrical work, and is responsible
for bringing the electrical equipment to a state of readiness for connection
to a source of electricity for use for its intended purpose, must ensure the
electrical equipment is tested, as required under subsections (5) and (6).
Maximum penalty—40 penalty units.
.Date of
inspection
Appliance
Visual
inspection
Earth
continuity

Insulation
resistance
a
RCD test current
30 MA trip time
Milliseconds
0h
180h Test butt
Polarity
= Correct
M
2/7/09
Refrigerator ( LG model
R100020 Serial 1004039832)
O.K
0.3
75M
N/A
N/A
N/A
N/A
2/7/09
Safetypac (Clipsal mod 56B,
serial 9987987)
o.K.
0.8
187M
a
22
18
a
2.19.28.B
Work Record required by Regulations
Electrical Safety Regulation 2002 Part 2 Electrical work
15 Certificate of testing and safety
This section applies if a licensed electrical contractor performs electrical work that must be tested under
this division.
(2) The contractor must, as soon as practicable after the testing, ensure that the person for whom the
electrical work was performed is given a certificate complying with this section.
(5) A licensed electrical contractor must keep a copy of a certificate given under this section for at least
5 years after the certificate is given.
Maximum penalty for subsection (5)—20 penalty units
Certificate of Testing and Safety
As per Electricity Safety Regulation 2002,Part 8”Electricity Supply”, Division 3 “Testing”, Regulation 159,”Certificate of Testing & Work”
Electrical worker who tested the
electrical work.
Phone
Licence No:
Details of work
Contractors Licence
Details of Electrical Contractor
Inspection Certificate No:
Acts, Regulations,
Codes of Practices & Standards.
Electricity Act 1994 & Electricity Regulation 2006
Electrical Safety Act 2002 & Electrical Safety Regulation 2002
AS/NZS 3000:2000. Incorporating Amendment No. 1 (September 2001), Amendment No. 2 (April 2002), &
Amendment No. 3 (July 2003). The Wiring Rules.
AS/NZS 3008.1.1:1998, Electrical installations— Selection of cables Part 1.1: Cables for alternating voltages up to and
including 0.6/1 kV—Typical Australian installation conditions
I certify that the electrical installation work listed above has been tested in accordance with the prescribed procedures and that such work is electrically safe
and complies in every respect with the requirement of the Electricity Safety Regulation 2002, regulation 159.
Signature of Electrical worker:
Date of Certification:
2.19.28.B
Manufacturer Specifications of disconnected & replacement
equipment.
When replacing any load you should be sure that the new
item is suitable with regards to: Speed, Rotation, Power
rating, Voltage, Current, Physical size, Environmental
conditions & design of replacement, Dust & waterproof,
temperature, UV rating, touch proof, life span.
2.19.28.C
Energising supply
• Only after the visual inspections and safety testing as
per AS/NZS 3000:2007 has proven that the circuit is
fit for purpose are you to energise the circuit.
• Remove only your Danger tag. If another worker has
their danger tag on the isolated point then you can
not energise.
• If clear: Energise the circuit.
• Test for the correct and safe operation of the circuit,
i.e. rotation, system performance, current draw,
voltage, etc.
• Prepare all your safety and performance
documentation.
2.19.28.C