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- 14 Nov 2004
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Can anyone help? I have tried wiring up my combined shower extractor/light as per the attached diagram but the RCD (not the MCB) on the distribution board feeding the shower continually trips when the light is connected. If the light is disconnected the fan runs perfectly.
I have done all of the following to check things out:
Turning off all the other MCBs on the same board as the shower MCB. It still trips.
Disconnecting the fan and connecting the light only. It still trips.
Wiring the light direct to the shower isolator. the light works and does not trip the RCD.
Wiring the light directly to each of the FCUs in turn. The light works and does not trip the RCD when wired to shower side or the MCB on the lighting circuit (the lighting circuit is on a different distribution board).
Checking the earth connections do not cross from the shower circuit to the lighting circuit.
Disconnecting earth wires into the two FCUs (plastic drywall boxes in use). Still trips.
Changing the wiring arrangement to ensure that a cable fault is not causing the problem. It still trips.
Connecting in a different lamp (normal 240v incandescent) rather than the transformer fed LV halogen. It still trips.
Wiring the halogen on the permanent live/neutral off the fan isolator. The light works and does not trip the RCD. Obviously it is on all the time since it is not on the switched live but hey, you cant have everything.
Have I missed something obvious?
My only solutions are to take the permanent live off the FEED side of shower isolator and a switched live off the LOAD side but this is not good as it bypasses the switch. Alternatively I could put in a relay to electrically isolate the shower and lighting circuits. Anybody else suggest anything?