DeltaB

I recently set up a 50 gallon (UK) marine reef tank with a 25 gallon sump tank. Now I only know what I had researched, mostly on this site!
I bought a Metal Halide lamp made by a Chinese company. Its a 150 watt unit with a separate ballast & the lamp clamps to the side of the tank. Nice looking & worked well for a few days. However our fuse box is modern and has 2 residual circuit breakers (rcb's) in it. For those who don't know an rcb detects when there is a leak from mains to earth, i.e. you touch the live wire, and it cuts out the supply before you get fried.
The trouble was that the MH lights started to trip the rcb at odd times. They might start and run for a couple of hours and then blow or they might just blow when you switched them on. I took them back to the shop and they replaced them with a new one, and surprise surprise they started doing it again. Two sets in 5 weeks.
The shop have now stopped selling them and we have come to a very amicable arrangement where I get a new set of lights costing more than I paid in the first place.
I presume the cause was within the ballast. From what I can find out there is a smoothing circuit within the ballast to prevent flickering of the light. This involves connecting part of the circuit to the earth vis a capacitor and this acts as an earth leak so tripping the rcb.
I used 2 rcb's a 32mA & 100mA both tripped.
Now this NOT a don't buy this product or anti MH, I'm just trying to point out a possible problem others may encounter. The main danger as I see it is if your system loses power in your absence and the livestock suffer. Luckily I didn't have that problem cos I am at home most of the time.

Tumbleweed

Thanks for the info. That is why in my tank my lighting system is run on a different circuit then the rest of the tank.

DeltaB

I would imagine a lot of people would see that as being the answer Tumbleweed. But in doing that you are installing a 'risk' factor into your system, in that if anything went wrong there is a danger of a possible fatal shock hazard. There's an excellent article on electrical safety on this site which suggests rcb's or similar units being used in the circuits. However the real answer is for the manufacturers to produce a product that doesn't cause the problem in the first place.

Tumbleweed

I have never run into that problem before with my lights. I wonder if it was just a problem with that manufactures product? My lights plug into a GFI circuit, so if there is a electrical issuse that circuit will trip and pretect me and or my tank/house.

DeltaB

I'm glad you have the foresight to protect your circuits that way. I was not being critical of your choice of circuit but I do want others to realise the implications of using an unprotected circuit.
As to whether its just a problem with the manufacturers product, I have to admit that when I drop a bit of buttered bread it always lands butter side down! So maybe it was just bad luck for me. Having said that there is still a lesson to be learned from this. Safety is paramount.