Earth Fault Loop Impedance:

Where protective measures are used which require a knowledge of earth fault loop impedance, the relevant impedance shall be measured, or determined by an equally effective method.

Earth fault loop impedance tests are carried out at the locations indicated below:-

• at the origin of each installation and at each Distribution Board
• fixed equipment and socket-outlets
• 10 per cent (on a random basis) of all luminaires, with a minimum of one luminaire, preferably the further one from the consumer units, for each circuit of any building
• at any location which may be exposed to exceptional damage or deterioration or represent a special hazard at the furthest point of every radial circuit

Where the installation incorporates an R.C.D., the value of earth fault loop impedance obtained in the test should be related to the nominal residual operating device.

Insulation Resistance:

Insulation resistance tests should be made on a dead circuit and any electronic equipment which might be damaged by application of the test voltage must be disconnected or isolated. The insulation resistance should be measured between each live conductor and earth and should not be less than 0.5 megohm. Where practicable the tests are applied to the whole of the installation with all fuse links in place and all switches closed. Alternatively, the installation may be tested in parts.

Operation of Devices for Isolation and Switching:

Where means are provided in accordance with the requirements of the Regulations for isolation and switching, a 10 per cent sample shall be operated to verify their effectiveness and checked to ensure adequate and correct labelling.

Operation of Residual Current Devices to B 4293:

Where protection is provided by an R.C.D., the effective operation of each R.C.D. shall be verified by a test simulating an appropriate fault condition independent of any test facility incorporated in the device, followed by operation of the integral test device. The nominal rated tripping current for protection of a socket-outlet for use with equipment outdoors or physically installed outside the general installation equipotential zone must not exceed 30 mAmp (0.03 amp).

In certain situations such as high risk areas, 10 mAmp RCD's may be appropriate for the particular installation.

For this information in PDF Format click (File Size 71KB)