rcbo tripping

mcm · Oct 27, 2011

anyone got any ideas on this.

Had to change a lighting circuit mcb to an rcbo due to cable we put into the wall (work is on a school). The old mcb was 15amp rated and 1.5mm twin and earth circuit. I changed the mcb to a 10amp RCBO but when I tried to turn on it tripped. so I thought it could of been tripping due to overloaded, I then changed the RCBO to a 10amp MCB and it was fine so no overloading. I then went around disconnecting the outside emergancy lights and trying to reset the RCBO. Got the first one on with the rest disconnected but when it came to the secound light it tripped. Byepassed the second onto the third and still tripped, then I disconnected the first light byepassing it and put the secound one on with the rest off it stayed in. Its like everytime a light is added it trips as if overloaded. the RCBO was type C as well any thoughts on this.

thanks

Guest112 · Oct 27, 2011

did you perform IR tests? if so what were the results?

telectrix · Oct 27, 2011

earth leakage on emergency lights. probably due to the electronics in them. each one will have a small leakage, but add all together and it takes the rcbo over it's threshold. try a ramp test with no load, then do it again with as many lights conneced as don't trip it. you'll probably see the trip current much lower.

tony mc · Oct 27, 2011

I would ramp test the RCBO first as Tel has mentioned as it could be faulty on the RCD side of it.

If this proves OK a IR test on your cct to make sure it is sound for the RCD to hold. It should hold above 7666 Ohms with a 30mA unit. (230/0.03)

You could try clamping the cct with a Earth leakage clamp meter but this a IR test should be done and you will require the readings for the paperwork!