Download How do you Need to Know for electrical equipment is safe

What do you need to know to
make sure a piece of electrical
equipment is safe?
There is a right and wrong way to test appliances. You can find information in the Standard
AS/NZS3760:2010 which covers not only how to test but also the environment for frequency of
inspection and testing which is now based around usage. Testing can be quick and easy if you have
good equipment and the right training.
What tests need to be done?
The correct tests required to be carried out on your Class I or Class II appliance in the following order:
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Visual Inspection
Earth Continuity Test
Insulation Resistance Test
Leakage Test
Further tests have to be performed on leads, RCDs etc
Before any testing can be carried out, we need to determin what type of equipment it is eg CLASS I
(earthed) or CLASS II (double insulated). What does this mean :
Class 1 Equipment
Class 1 electrical equipment is equipment that relies on the Protective Earth and basic or single
insulation for its safety - such items usually have quite a lot of exposed metal and are often quite
heavy. Some examples of Class I equipment could be dishwashers/washing machines/irons/fridges/
electrical machinery/drill presses/saw benches/bench grinder etc, But some small appliances like
hand drills, saws, plainer can also be Class 1. Modern hand held tools today are usually Class 2
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This type of appliance is often referred to as an 'earthed' appliance
Class II Equipment
Class II electrical equipment relies on two effective layers of
insulation.
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This type of appliance is often referred to as a 'double
insulated appliance
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It will normally be marked with the doublebox symbol
Note:
Most modern electrical hand held equipment is Double Insulated but we must confirm this
as part of our testing process.
RCD (Residual Current Device) - an RCD is used for increasing electrical safety and is
designed so that it will disconnect the power when the residual current (That’s current that could flow
through the body) reaches or nears a preset value. For RCDs designed to protect people this figure
must be less than 30 milliamps.
Isolation Transformer - this is used for increasing electrical safety and is designed so that the
two sets of windings (Coils) (the primary and secondary) are separated from each other by at least
the equivalent of that required to achieve double insulation, thereby ensuring that the electricity from
the secondary (output) side is isolated from earth.
EPOD (Electrical Portable Outlet Device) - this is a multiple outlet device and will commonly
be called a multibox in New Zealand or a power board in Australia.
How to carry out the testing:
The Visual Inspection (this test is carried out on all types of equipment)
This is very important as approximately 90% of faults can be found by this inspection. The Visual
Inspection is not just an check for broken parts; it basically everything about the appliance. The
basic requirement is that it should be as it came from the manufacture when it was new.
This part of the testing process may involve:
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Smelling
Pulling on leads
Tapping the appliance
Check for cracks or holes, no missing screws or other components
Shaking nothing is loose or broken
Turning some part/s, any locks or retaining screws
Checking by trying to see that retractable guards actually retract... and all manner of other
things may be done to ensure that it is safe to operate.
Then depending on whether the equipment is Class I or Class II the following tests are done:
For Class 1 (earthed) equipment
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Earth Continuity Test - this may be done with an Ohm Meter or a Portable Appliance Tester
(PAT). The Standard AS/NZS3760: 2010 requires that the resistance is less than 1 Ohm or
alternately an electrical test current for PATs of 100mA to 25 Amps.
Insulation Test/Leakage Test - a leakage test shall be done on appliances that have internal
switching that is only activated when the equipment under test is powered at operating voltage.
For equipment that does not have internal switching as above then a 500 Volt insulation test is
an acceptable alternative.
For Class II (double insulated) equipment
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Insulation Test or Leakage Test - a leakage test shall be done on appliances that have internal
switching that is only activated when the equipment under test is powered at operating voltage.
For equipment that does not have internal switching as above then a 500 Volt insulation test is
an acceptable alternative.
For Cord Extension Sets
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Earth Continuity Test
Insulation Test or Leakage Test
Cord extension sets with re-wireable plugs fitted need to also have, in addition to the above tests, a
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Polarity Check
The Fittings (Plug & Socket) also must meet specific safety requirements
For RCDs
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Earth Continuity Test
Insulation Test or Leakage Test
Trip Time Test - in addition to the above tests RCDs shall have a trip time test performed on
them at the time period specified in Table 4 AS/NZS3760: 2010
Tests required in more detail:
EARTH TESTING
The difference between using a Multimeter and a PAT Tester with a high current earth bond capability
is that a Multimeter does a Continuity Test where as a PAT Tester does an Earth Bond or Earth
Integrity Test. The PAT test is far superior and will show up more faults.
There is a VERY BIG DIFFERENCE between the two tests.
Legally it is a requirement - but is it really necessary?
Potentially the most dangerous appliances are Class I appliances (earthed appliances) eg microwave
ovens/bench grinders and the like, but also in this category are extension leads. Class I appliances
are designed to have an earth - this means that in the example of a hand held drill the metal body of
the drill is connected to earth - literally to the ground via an earth conductor which goes right back to
the building switchboard and then into the ground the building is sitting on. If this conductor is
damaged anywhere then the consequences can be fatal. It is obvious therefore that this conductor
needs to be tested.
How can this be done properly?
Unfortunately, most people believe they are carrying out the testing properly if they are using a
Multimeter, but this types of instrument will not usually pick up an earth fault unless there is a
complete break in the conductor.
There is another type of tester available on the market that people, including many electricians, may
not be aware of - it is called a Portable Appliance Tester or 'PAT' for short. The PAT is specifically
designed to test electrical safety and does all the different tests necessary to ensure the electrical
safety of the appliance and makes testing easy.
IMPORTANT NOTE: Its very important to first ensure that the Earth is satisfactory before undertaking
the Insulation Resistance Test
Doing safety testing with just a Multimeter or similar type of instrument is NOT SAFE. An earth
conductor substantially damaged or not there means that in a situation where a fault occurs the
operator becomes the earth ie the operator becomes the means by which the active 230 Volts supply
returns to earth - likely killing the person in the process!! It is essential that when an earth conductor
is needed that it is able to pass the earth current required otherwise you or someone else will become
the earth.
You should by now be able to see the difference between an Earth Bond and Earth Continuity Test ie
an earth bond test shows whether the earth conductor is in a satisfactory condition; whereas an Earth
Continuity Test (100 milliamps or less) using Multimeters and the like will possibly only show the earth
is connected, not its' condition.
INSULATION RESISTANCE TESTING
Insulation Resistance Tests must not be carried out using Ohmmeters or Multimeters because these
meters only produce a small battery voltage in the region of 1.5 to 9 volts. This small voltage is
insufficient to pressure test the insulation to expose any weakness in it and therefore is totally
inappropriate for Insulation Resistance Tests.
Insulation Resistance Testers and PAT Testers on the other hand are specifically designed to
produce 500 Volts (or even greater voltage values for some applications) which places the insulation
under stress. This test will indicate any weakness that may break down under normal use on the 230
Volt supply. Itis a requirement that the resistance measured by the Insulation Tester in this way
should be not less than 1 Megohm (1,000,000 ohms) for an electrical appliance to pass this test.
A practical example showing how a Multimeter or Ohmmeter is inappropriate to test the insulation
resistance of an electrical appliance is detailed by the following example:
A 230 Volt floor polisher has a partial insulation breakdown between the motor windings and the
earthed metal case. The polisher when in use and at its normal operating temperature, causes the
sub-circuit protective fuse to blow as a result of the insulation breaking down to the earthed metal
frame.
The polisher, when tested with an Ohmmeter or Multimeter, does not indicate the presence of a fault,
as the meter voltages are so low that they do not stress the insulation and therefore do not reproduce
the breakdown that occurs when the appliance is in use.
However, testing the same polisher with an Insulation Resistance Tester producing an output of 500
Volts causes the insulation to break down under test, thereby indicating a low insulation resistance
value and the presence of a fault path.
NOTE: The importance of a sound low resistance earth continuity conductor is paramount to the
safety of any electrical appliance that requires an earth. A test as described above would not achieve
anything if the integrity of the earth were not first proven to be in good condition. Should the appliance
have an open circuit earth continuity conductor, it would produce a high resistance test result, but in
fact when the appliance was plugged in it would enliven the case and expose a potential shock
hazard.
Alternative Leakage Test as required AS/NZS3760:2010
LEAKAGE TESTING
This test was first introduced in the 2003 version of the Standard and it can be used to replace the
500 Volt Insulation Test.
The advantage a Leakage Test has over and above the 500 Volt Insulation Test is that the Leakage
Test when carried out on an appliance at operating voltage ensures the whole of the appliances'
circuitry is fully tested. The old 500 Volt Insulation Test would not fully test many appliances ie those
with internal switching that required operating voltage to activate switches. Hence an appliance may
test safe and not be, when tested with a 500 Volt Insulation Test.
Some fatalities could have been prevented if a Leakage Test had been done instead of the 500 Volt
Insulation Test.
NOTE: A 500 Volt insulation test is an adequate test providing all of the appliances' circuitry can be
tested using this method.
RCD USE & TESTING
Unfortunately we can all be careless around electricity -RCDs can give limited protection against a
fatal shock
An RCD is specifically designed to minimise the risk of a fatal electric shock when working with
electricity. It is an electronicsensing device which constantly monitors the balance of the current flow
in the live and neutral conductors to ensure that should even a minor leakage occur the RCD will
switch off the power within 300 milliseconds (for personal protection RCDs) ie in less than the time of
a single heartbeat -which could mean the difference between life and death.
You need to remember the following:
1. When properly connected an electric current flows through the live wire on its way to the
appliance and returns to the supply circuit via a neutral wire
2. If for some reason the current 'leaks' (through dampness, frayed wiring, faulty connections etc)
the current will take the most direct path to earth - often through a persons' body. In this
situation if the power is not disconnected instantly then there is a strong possibility that the
person will die.
3. The path taken by the current also contributes to the severity of the electric shock. An electric
shock that flows from the hand through the arms and to the chest will affect the breathing and
heartbeat.
4. The greatest contributing factor to the severity of an electric shock is the exposure time to the
current. An RCD cuts off the power in less than the time of a single heartbeat
Testing an RCD can be done in 2 ways:
1. A push button test on the RCD, requires no test instrument but it is NOT A SAFETY TEST .
2. By the use of an RCD Tester, an RCD Tester is designed to check the trip current and trip time.
Most RCD Testers can measure the trip time from 1 millisecond to 2000 milliseconds and the trip
current which must not exceed 30mA or 10 mA for RCD that protects children, sick people or the
elderly.
Safer Site Appliance testing courses cover all of this information in detail and comprehensive
handouts are provided along with practical hands on testing experience on real appliances.
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These courses can certify you as a competent person to legally test appliances.
Contact: Kerry Harris. 021 722493, Email
: [email protected] Web www.safersite.co.nz