by ericmark »
Sat May 10, 2014 4:52 pm
There are many reasons for a MCB to trip and even more for a RBCO to trip so I will try to list common causes for a MCB to trip.
1) Has to be faulty MCB however this is normally due to persistent overloading so first look at other reasons.
2) Wrong size fitting for the 6 amp supply. Because we have ceiling roses and the like in the main we are limited to a 6A supply. However the silly 50mm spot lights can easy cause this limit to be exceeded 1380W seems a lot but I have seen 12 spots in a kitchen that's 600W for just one room. Where these silly spots are used often the supply was spilt up and down stairs but when RCD's are added often it has to return to single 6A supply because of shared neutral problem with two way lighting.
3) Fault item on the lighting circuit. Be it an outside light filled with water, a shaver socket overloaded with tooth brush and caused transformer to burn out or a bathroom extractor fan burnt out often these don't have the isolation they should so can't be switched off to test.
4) Cable damage. It has just been reported on how a plaster put a nail through a cable and caused the death of a woman. The problem with these sort of faults often they do not become evident until some thing else happens as well. Could be as simple as walking on floor boards above the fault or some water spillage as with the case reported.
5) Poor bulb manufacturer. In theroy every bulb should have a built in fuse. The BA22d bulb holder is often only rated at 2A so even with CFL and LED the fuse should still be there. With a standard bulb it was there in case on blowing the gas in the bulb becomes ionised and as a result is like a short circuit often inside of the bulb goes black. I found bulbs from Ikea did not have the built in fuse only way is to remove all bulbs and replace one at a time.
I am sure there are many more. Where it's a RCBO or RCD tripping then there are many more reasons including borrowed neutrals. However with so little information can't really help much.
