Testing and Test Instruments 79
Table 3.6 RCD Type
Half Rated
Full Trip Current
BS 4239 and BS 7288 sockets
No trip
200 ms
BS 4239 with time delay
No trip
–12 time delay 200 ms to time delay 200 ms
BS EN 61009 or BS EN 61009 RCBO
No trip
300 ms
As above but Type S with time delay
No trip
130 t 500 ms
FUNCTIONAL TESTING RCD/RCBO operation Where RCDs/RCBOs are fitted, it is essential that they operate within set parameters. The RCD testers used are designed to do just this, and the basic tests required are as follows: Set the test instrument to the rating of the RCD. Set the test instrument to half rated trip. Operate the instrument and the RCD should not trip. Set the instrument to deliver the full rated tripping current of the RCD. 5. Operate the instrument and the RCD should trip out in the required time. 1. 2. 3. 4.
There seems to be a popular misconception regarding the ratings and uses of RCDs in that they are the panacea for all electrical ills and the only useful rating is 30 mA!! Firstly, RCDs are not fail safe devices, they are electromechanical in operation and can malfunction, and secondly, RCDs are manufactured in ratings from 5 to 500 mA and have many uses. Table 3.7 illustrates RCD ratings and applications.
