Lights blowing mcb

[WELLSIANA]

So whats is your ideas...5 amp mcb with main switch 30ma rcd....nice house , dry etc ...put any combination of lights on and after around 4-5 minutes mcb blows.....the lambs are varied but i can not see any overload and it will do it with only a handful on...if you leave say 1 or 2 lights on it will not blow...and any selected but add load in any are even light it blows...so far my views is could be mcb fault but then why would it not blow with less lights...small fault...but why would that not take out rcd ?..and this has been doing it for years not short term...a mcb blowing seems overload but i can not see that as it does it well in on loading...any views ?

 

[Deleted member 9648]

IR test the circuit both LN-E and L-N (with lamps removed).An RCD will trip on a low IR to earth,it will not trip on a L-N fault,that would trip the OCPD.Eliminate that first. If IR is satisfactory clamp the line and see what the circuit is pulling.
My guess would be a 'tired' mcb. But test for faults first.

 

[Richard Burns]

Possibly on the MCB (bus bar or terminal) a loose connection that heats up with more current drawn and so causes the MCB to trip on thermal overload despite the load not being high?

 

[WELLSIANA]

yeah going for the mcb first .. if not i will be taking lamps out and testing as described or some disconnections...certainly its not overload....is there anything else on the thermal overload i am missing? there is extensive dimmers...some of the non fire rated downlights ..but not many...if a dimmer was erratic would it cause this rather than show a dimmer breaking down...gut feelings.

 

[Pete999]

Clamp the circuit to see what it's pulling.

 

[Leesparkykent]

If everything has tested fine and you have checked the connections on the mcb as Richard has said . if there is another lighting circuit swap the circuits between the MCB's and see if it does the same thing.

 

[Darkwood]

Have you clamped the load ... unless you wired them yourself don't assume that no other loads are tapped into the circuit.
Have you done any testing and if so what results?

Also check post 3 as a possiblity.

 

[WELLSIANA]

no tests at the moment as i am just throwing it out to see views...the clamping the load i understand but its does it with very little load but an increased load...i mean 5 amp mcb blowing with say 500ws on but held at 400ws...also turn the light off in lounge and put dining room on does the same yet load could be 500 or less...keep on light or two on say 300w any variation holds fine...so i am thinking along your routes and will go that path.....no other items other than the lights are affected when it blows so i assume no sockets took off it......etc...good one isnt it and i have 35 years...i like these ...i admit the con unit is older but apart from rcd control i could not tell them its HAS to be renewed ...

 

[123]

Fault finding, and no tests done? Deary me!

RCD may not trip because it's goosed. Get the tester out and test. My very first port of call would be to check the RCD is operational.

 

[Deleted member 72666]

Well what's the point in not testing, it could be a number of things, all that everyone's doing is guessing! Get some tests done and take it from there. If it was me I'd clamp it first to rule out excessive load then carry out further tests if needed. It could even be an earth fault and the rcd is stuffed! Without testing you'll never know. I would have thought with 35 years experience you'd know that.

 

[7029 dave]

Well it's obviously not short circuit, clamp it and see what kind of load your pulling.

 

[WELLSIANA]

With 35 years i do know that...was a simple chuck it out there to see what as "electricians" your views were...not guessing as such just time served hunches...of course i will be going down all the routes but i thought i would ask to see if anyone came up with a thought i had not considered. i have not done any tests yet as i have not started although i have been to see the problem ...most of us know the routes but surely you have come across the sparky that says "i had that once ..guess what it was " or would you say i can not guess unless you tell me you tested... i only seeked to see views on hunches not be treat like a schoolboy

 

[Paul.M]

You have been given some very helpful advice and I can not see why you have such an attitude towards other members replies? You have only just stated that you have not had the chance to carry out tests, only looked at the job. If you told us this in the first post things would have been a lot clearer.

 

[Darkwood]

With 35 years i do know that...was a simple chuck it out there to see what as "electricians" your views were...not guessing as such just time served hunches...of course i will be going down all the routes but i thought i would ask to see if anyone came up with a thought i had not considered. i have not done any tests yet as i have not started although i have been to see the problem ...most of us know the routes but surely you have come across the sparky that says "i had that once ..guess what it was " or would you say i can not guess unless you tell me you tested... i only seeked to see views on hunches not be treat like a schoolboy

Although the mod has already edited your response may I offer advice, your profile about your electrical experience hasn't been filled nor did you present this in your opening post thus we don't know if your still wet under the collar with minimal experience or as you have now revealed you have 35yrs under the belt, this puts us in a difficult position of guessing how to respond ... to a newby all above advice is relished but to someone with 35yrs experience you may feel your been condescended hence your response but until we are told we have to guess and usually this is done by the nature of the question.

Asked the same question on site then I would talk totally different to a seasoned sparks like yourself than a newby on his first year qualified.

 

[Deleted member 72666]

With 35 years i do know that...was a simple chuck it out there to see what as "electricians" your views were...not guessing as such just time served hunches...of course i will be going down all the routes but i thought i would ask to see if anyone came up with a thought i had not considered. i have not done any tests yet as i have not started although i have been to see the problem ...most of us know the routes but surely you have come across the sparky that says "i had that once ..guess what it was " or would you say i can not guess unless you tell me you tested... i only seeked to see views on hunches not be treat like a schoolboy

I'm guessing that the 'condescending' line that was removed was aimed at me,if so, am I bothered....no, skins far too thick and besides I grew a pair a long time ago! What I will say is that it sounds like an interesting fault which most on here including myself would relish the task of sorting, and if found to be rather odd or unique would then start a thread sharing the information gained. I know 1 or 2 on here who would even drip feed information and set it out as a 'see who's first to guess what the fault was' quiz.
You could gain a lot of respect by coming back on here and reporting your findings, that I can guarantee will be well received.