Here is one that Mike will enjoy
At the new installation, the control boxes were tripping the RCD (Earth leakage) protection of the building when the "door" isolators/disconnects were turned off (broken). There was no problem during the switch on. Turns out that Jordan wired the internal cooling fan between the isolator and the contactor, as follows:
Instead of as per the drawing as follows:
Because the fan was turning, just before switching off, it generated a small current. Because the manual door switch is slow, it doesn't lift all its poles simultaneously and this small current exceeded the 30mA allowed by the RCD Earth Leakage device. Moving the fan supply to the other side of the contactor cured the false tripping.
Tue 19 May 2009, 06:27
