downstair lights - mcb tripping

[dannynolan]

I have an MK electric consumer unit with a 6amp mcb for the downstairs lights.

Whenever I switch on more than say 4 lights the circuit breaker trips (just the 6amp one relevant to the downstairs lights, not the main one for all the electrics).

It does not seem to matter in which rooms the lights are or the type of light (a mixture of "old fashioned normal", newfangled eco friendly, halogen kitchen spots and under (kitchen) cabinet strip lights). Ie. a total wattage of less than 400 can be enough to trip it.

I've had this problem for a long while and can't relate it to any electrical work being done.

Any help greatly appreciated.

 

[EFLImpudence]

The topic tiltle says RCCB tripping and in the text you say 6A breaker.

 

[dannynolan]

Well done , Wilson - I was wondering who'd be the first to spot that

Many thanks - duly edited.

 

[securespark]

Could be a dodgy breaker, that's tripping before its time.

Maybe swap the wires on upstairs and downstairs lights around.

If you get a tripping on the upstairs lights, it's a dicky breaker.

The fuse company can sell you a new one.

 

[EFLImpudence]

As it is an MCB that is tripping it must be due to either -

an overload, which is not possible with only 400W, or

a short circuit which could be caused by a wire moving when heated and connecting with another.
It could be one of the lights taking time to heat rather than because four are on - unless, of course, you are using a different four, or

not unknown, a faulty MCB.

I suggest swapping the MCB for a new one one or swapping the Live conductors on two 6A MCBs to see if the 'other' or 'same' one trips if you are competent (legal term) to do it.

This will be an easier first test than trying to find a faulty wire.

 

[dannynolan]

Thanks to both for your replies.

Will look into swapping mcbs tomorrow.

Just tried it again - had a total of 350 watts switched on and "added" a light in a room not normally used (under the stairs) and it tripped. So, yes, it's not overloading or overheating of one light in particular.

Hopefully will sort it out tomorrow - will let you know - thanks again.

 

[PrenticeBoyofDerry]

As above post, you could have a short that only happens when cables/lampholders are heating up on load or a faulty MCB.
So a little investigation in switch plates and light fittings, MK B types are about £3.

 

[riveralt]

Sounds very similar to a job I went to recently except the circuit was the downstairs socket radial circuit. Once a certain number of appliances (different ones each time) were energised the MCB tripped - there was no RCD protection.
Before doing any testing I got the owner to try and repeat the trip while I watched the Consumer Unit with only that circuit energised.
After turning on a few appliances - sparks appeared in the CU and it turned out to be a damaged neutral conductor at the neutral bar.
Might be worthwhile observing the CU (at a safe distance) with just this circuit energised while trying to repeat the trip.
I hesitate to say look at the wiring inside the CU or change the MCB (they very rarely go) because in certain circumstances parts of the CU will still be live and as others have said - you need to be competent and confident you know what you are doing.
The alternate approach without touching the CU is, while the circuit is dead, check each switch and ceiling rose for a loose connection or signs of damage to the conductors or the terminals.

 

[dannynolan]

again thanks for all the help

 

[ban-all-sheds]

Any change in what's going on?

 

[dannynolan]

Out of courtesy and to help anyone else with the same problem.

We called in a local sparkie, very reasonable at £35 a visit North London, who took out the relevant MCB. It was scorched and slightly cracked. As an interim measure he switched it to an upstairs light circuit - problem solved.

He then bought a replacement online (second hand as original out of production), tested it by shorting, and overloading it with an electrical fire, and put it on the rarely used doorbell spur.

Incidentally, most of the brainwork on this was done by my OH who in her time has completely wired a house, stripping out the old wiring, installing four circuits, a line to the cooker, test and connect by local board chap, and off we went.

So if there's any ladies out there that fancy a change of career, and want to train up as a sparkie, don't be put off. Being very patient, a very good planner, and very thorough (as my OH is) helps.

Thanks again to all contributors.

 

[ekmdgrf]

If the XYL has rewired a house, why didn't she swap the MCB and save you £35?