RCB trips on lightcircuit when bulb fails. Socket RCBs trip

[kenlinda]

The RCB's on the light circuits tripped every time a light bulb failed.

The RCB's for the 13 amp sockets tripped when too many applainces were switched on (eg:- w/mach, d/washer, kettel and TV/video etc in living room all together on same loop). Cooker/shower/alarm etc each have their own 32/40 RCB with no problems.

A spark 'friend of a friend' changed both my 6 amp lighting RCB's to 16 and both the 16 amp socket RCB's to 32 amp. This seems to have solved the problem.

But I am worried that 6/16 should have been enough for a normal wimpy semi and that uprating them may just be masking the underlying problem. Am I right to be worried or is this a common and relatively safe way to solve such a problem?

You reply may just help me sleep better at night!

 

[Adam_151]

I think you mean MCBs

If you have a ring circuit for your sockets they should be on a 32A breaker, most socket circuits atm are rings, but as I can't see your house I don't know if yours are, but if they are rings, then the question must be asked is why were they on 16A breakers to start with. If you have a 16A circuit and it covers the kitchen then you are likely to have nuisense tripping.

You also get nuisence tripping when a lamp fails on a B6 breaker, the correct solution involves changing to a type C, 16A breaker on a lighting circuit is very unlikely to comply (unless the lighting circuit was designed with this in mind, which it won't have been in a house)

 

[kenlinda]

Many thanks for the swift reply.

By C do you mean a C6 or a C16 (if there is such a thing) for the lights?

The new board was fitted by another spark friend of the same friend a while back, so he was the originator of the 16 amp ring socket MCB's. May explains why he was always coy when I asked him why it kept tripping.

One of the lighting 16 amp MCB's also works an above head height socket in the kitchen (as well as the downstairs lights). I have rarely used it and don't know why a previous owner may have wanted it there.

Would a C still be the best MCB for that lighting(& 1 socket) circuit or am I better leaving it as the 16amp.

 

[comms]

personally I'd get a sparks in to test & not your friend of a friend one.
Adam is on about a C6 (6 amp) mcb for the lighting circuit, it should stay on when a bulb blows.
Unless as Adam says the circuit has been designed for it, a 16 amp mcb is a little on the large side for a household lighting circuit.
On the 16amp ring, at a guess when your friend of a friend changed the cu bet he tested the ring for continuity at cu found it to be broken ( no continuity) so stuffed a 16amp mcb in. but alike adam say's with out looking who knows ( it could be a radial circuit).

 

[Adam_151]

Many thanks for the swift reply.

By C do you mean a C6 or a C16 (if there is such a thing) for the lights?

Sorry, wasn't clear, I mean C6

The new board was fitted by another spark friend of the same friend a while back, so he was the originator of the 16 amp ring socket MCB's. May explains why he was always coy when I asked him why it kept tripping.

I suppose it could have been a broken ring (if thats the case, having it on a 32A breaker now is not a good idea), but if that was the case, then an electrician would have normally asked you whether you wanted to pay for it fixed, or just have the damaged part removed and made into two 16A radials (doesn't really make sense to put it on one)

One of the lighting 16 amp MCB's also works an above head height socket in the kitchen (as well as the downstairs lights). I have rarely used it and don't know why a previous owner may have wanted it there.

You shouldn't have sockets on the light circuit, though people do sometimes add them for things like wall mounted televisions, would advise that it be removed

Would a C still be the best MCB for that lighting(& 1 socket) circuit or am I better leaving it as the 16amp.

It is unlikely that the cable is rated at 16A, thus it should not be on a 16A breaker, changing from a B to a C gives leeway on the magnatude of the short surges that occur say when a lamp fails, without giving the circuit free-reign to draw a larger continuous current.

(B types tolerate a short surge of 3x the marked rateing, its 5x for type C)
A B16 is very unlikely to be the right choice for a domestic lighting circuit, B6s are commonly used, but commonly nuisense trip, C6 usually avoids this problem, sometimes if there is a lot of lights a B10 or C10 might be used

 

[mottsy]

Sorry to jump in on this thread, but I have plug in type B6 MCB's on my lighting circuits. (By plug in, I mean they have replaced the old wired fuses in my CU.)
I have the same problem of them tripping when a bulb fails. Can I get these C6 ones that plug in. I had a quick look at screwfix and toolstation but could only find B6 ones.

Many thanks

Mottsy.

 

[Steve]

dont think they do C6's for plug-in boards.

Fit cartridge fuses - these shouldn't blow when a bulb goes.

 

[Adam_151]

BS1361 fuses are your best bet for lights tbh if you still have a wylex standard CU

(sidenote: of course, before changing circuit protective devices you should check your ELFI at the end of the circuit)