Thread: Safety switch problem?

Attention sparkies. Shortly after moving into our house 14 years ago I had a company come and install a safety switch in the meter box. This has been tested and works well. My problem now is that I have two fluro lights wired on a two way circuit. Twice in the last couple of days as I switched them off I have blown the safety switch. I was under the impression that this safety switch was monitoring the power circuits, not the light circuits. Both times the switch tripped it plunged the house into darkness but left the power outlets on. I think I have a problem somewhere. I was thinking that maybe the fluro lights pick up power from the power circuit, but if that was the case the safety switch would kill the power circuits, which is not happening. Any suggestions, before the house catches alight?? Jim

I'm going to guess that the fault in the lights circuit is inducing a current surge in an adjacent power cable causing the RCD* to trip out. I remember being surprised in my first house when I tripped a breaker in the shed with a major machine fault, which then caused the house RCD to trip in sympathy. The house was 20m away on an underground feed from the shed which had the meter box on it.

Your fault may be in one of the fluoro lights, try taking one tube out. It may also be in one of the switches if a looping terminal is being used. A separate blue point for the looped cables might help. I had a lights circuit once that would occasionally flash over to the loop when switching a load.

If you can get in your roof space it might pay you to see how closely the power and lights cables are run.

Finally you might have a smaller current surge if you use replacement LED tube in the fittings, they use half the current and don't run through the iron ballast if fitted properly. They're unlikely to surge and light up to full brightness in a flash.

*RCD = residual current device, aka safety switch or earth leakage breaker.