RCD Use & Testing

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Unfortunately we can all be careless around electricity, RCDs can give limited insurance against a fatal shock.

  
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.
 
 
TESTING OF RCDs

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!

 

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.

Note

 

 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.  
Information on EARTH TESTING   Information on INSULATION & LEAKAGE TESTING