2.4.4 -  Compatibility

One part of an electrical installation must not produce effects which are harmful to another part. For example, the heavy transient starting current of electric motors {7.15.1} may result in large voltage reductions which can affect the operation of filament and discharge lamps. Again, the use of some types of controlled rectifier will introduce harmonics which may spread through the installation and upset the operation of devices such as electronic timers. Computers are likely to be affected by the line disturbances produced by welding equipment fed from the same system. 'Noisy' supplies, which contain irregular voltage patterns, can be produced by a number of equipment's such as machines and thermostats. Such effects can result in the loss of data from computers, point-of-sale terminals, electronic office equipment, data transmission systems, and so on. Separate circuits may be necessary to prevent these problems from arising, together with the provision of 'clean earth' systems.

Very strict European laws limiting the amount of electromagnetic radiation permitted from electrical installations and appliances apply from January 1st, 1996 (the Electromagnetic Compatibility, or EMC, Directive (see {6.6.2}). Equipment and installations must:

1. not generate excessive electromagnetic disturbances that could interfere with other equipment's (such as radio sets), and

2. have adequate immunity to electromagnetic disturbances to allow proper operation in its normal environment.

(For further details see The Guide to the EMC Directive 89/336/EEC, Second Edition, by Chris Marshman also published by E.P.A Press.)