Help with a lighting fault please?

[smileroutkast]

hey guys!

i was at a job 2day where the MCB in the kitchen of a pub kept tripping out. what was strange is that it wasnt tripping straight away. it would take ten mins or so before tripping out. i disconnected the lights one at a time (the kitchen is only small and has 2 fittings plus an emergency bulkhead) and that didnt help me in finding what was up. i then disconnected the switch n connected it thru with connectors n that didnt help either. any ideas on what the problem might be? if it helps, i cant get above the ceiling either ive gotta go back tomorrow mornin so immediate responses would be greatly appreciated

 

[sparkytim]

Possible overload of circuit holding for a while.

whats the load? whats the size of the Mcb?

If you have a clamp meter see what the circuit is drawing.

 

[smileroutkast]

the MCB is B6, i thought that and mentioned it to my manager n he said it wouldnt of been the issue. it has 2 twin flurescent fittings and an emergency bulkhead. is that enought 2 overload? unfortunately i dont have a clamp meter, what size MCB would u recommend? a C6 or maybe a B10? im not sure as i dont have a great deal of exp

 

[tom1]

i had this the other day, turned out to be low ir, cleared the fault and all working

 

[Doc Hudson]

As Tom suggests, Any tests done R1R2, ins-res? Any sign of cable breaking down under load?

Doc H.

 

[batty]

How longs it been doing it. Not likely to be overload probably fittings have overheated so could be choke going down or choke has overheated and shorting cables at some point. An insulation test is whats needed if you have not got tester take fittings apart and look for shorts overheated chokes usually are brown and smell burnt. Is there only three fittings on circuit.

 

[smileroutkast]

i dont have any test gear, i have continuity testers and thats about it. ive been given a new fitting and told 2 check the connections by my manager which is about as useful as a chocloate teapot, i was thinkin insulation resistance but i need testers for that. how would u clear the fault if it were low IR? jus curious

 

[smileroutkast]

i checked each fitting and they all look healthy. no smell at all. they look fairly new to be honest. theres no chance of them goin brown yet, they havent even gone yellow yet. they look new. i dont know how long its been goin on cuz i only got there today, the call was put in yesterday so im guessin then

 

[batty]

I would be suprised if they are the only fittings on circuit does anything else not work when it trips?

 

[Robin Spark]

Is there any build up of contaminants or moisture in any of the light fittings that could cause current to find its way from one of the live conductors/ control gear to earth?

Have you got an Insulation resistance tester? If yes connect L&N together and test to earth.

If you have a low reading then either a problem at one of the fittings or possibly a fault elsewhere.

If you have a Low IR reading then take the cable out of each luminaire one at a time, terminate into choc block to keep radial intact and retest IR each time. Hopefully this would lead to higher IR reading showing that luminaire is causing the fault.

Would also ask pub manager if they had any building work or alterations done recently, is there adequate ventilation in the kitchen.

How old are the luminaires? I am not sure but somemone else might know of a problem where control gear might cause a problem but this is usually on start up I would have thought.

Oh ignore my post I dont type quick enough and there have just been a few posts put on forum, oops!

 

[smileroutkast]

yea they are the only fittings on the circuit as far as i know. i'll take a more thorough look tomorrow

no theres no moisture or anything anywhere near the control gear or the conductors. i dont have an IR tester. theres only a small window in the kitchen, but then again it is a small kitchen. it takes a good 10 mins or so before it trips. but if i have the switch turned into the on position when i turn the MCB on it trips right away, it only stays on when i turn the MCB on first and then operate the switch

 

[Theorysparky]

you say 2 of the fittings are in the kitchen ???

is there an extractor fan in there on the cct ???/

 

[smileroutkast]

na theres not at all. jus 2 vapour proof fittings and an EM bulkhead. the kitchens not very big at all, i think they use the windows 4 ventilation, not too sure

 

[Theorysparky]

ok then i would change the mcb...

try to change the easy things if you are lacking the proper test kit

 

[smileroutkast]

what MCB would u recommend changin it too? at the mo it has a B6

 

[smileroutkast]

to*

 

[monkey5]

what MCB would u recommend changin it too? at the mo it has a B6

i wouldnt change it, the fault needs to be found TBH

wayne

 

[Robin Spark]

I think Theoryspark is saying replace the MCB with a new one. Another B6 type will be adequate for 3 luminaires especially as its the surge in start up when the luminaires light up is what would normally cause the mcb to open.

Is there another B6 breaker in the consumer unit that you could easily swap over to see if that works ok?

 

[nicks electrix]

i would try another B6 first just in case it is the mcb. I would not go any bigger than 6. That is more than big enough for what is on the circuit. Type C breaker has a bit more tolerance to sensitivity. However if you change the type of mcb from a B to a C You would then have to test the earth fault loop impedance of the circuit because C has a lower permissible value.

 

[smileroutkast]

yea i was thinkin that 6 would be more than enough. i know the fault needs to be found but if i dont have the test gear than what am i to do? im guessin from peoples comments i need to do an IR test