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Unfortunately
we can all be careless around electricity, RCDs can give limited insurance
against a fatal shock. |
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| An RCD is specifically designed to minimize the risk of fatal electric shock
when working with electricity. It is an electronic sensing device which
constantly monitors the balance of current flow in the live and neutral
conductors to ensure that should even a minute leakage occur
the RCD will switch off the power within 30 milliseconds (for personal
protection RCDs) i.e. in less than the time of a single heartbeat.
This could
mean the difference between life and death.
We 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 ground via the 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 person’s
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 which
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.
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TESTING OF RCDs |
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An RCD can be
tested in two ways:-
1. A push
button test – this requires no test instrument.
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 from 1 millisecond to 2000 milliseconds. Obviously
this trip time test can not be done with an ordinary stop watch!
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Many RCD Testers will be capable of conducting both an AC
and DC test, however in New Zealand to meet the requirements of AS/NZS3760
no DC test is required. |
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Note
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The Standard AS/NZS3760
requires that RCDs are tested for trip times at specified intervals i.e. not
just a push button test. An RCD Tester is required for this tripping time
test. |
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