Strange MCB Tripping

[newsparky]

Afternoon all,

Got called out to look at some external lights in a block of flats as management company said they were not working.
They are operated by a C10 MCB and wired via a photocell.
When I reset the MCB and cover the photocell the lights are all fine.
After speaking to a couple of tenants they said the lights just switch off over night.
First assumed it may have been rain as 2 lights were smashed so replaced them.
IR tests are all fine so am a bit stumped as to why they randomly trip the MCB over night?
All suggestions would be much appreciated.

 

[Leesparkykent]

What fittings are they, 2d?

 

[Guest125]

Could be a faulty MCB. Might be worth visually inspecting all the lights also. Remember rule number 1 though :

Always ignore what the client says and work it out for yourself.

 

[newsparky]

Yeah all 2d plus 3 son

 

[Engineer54]

Are you saying the MCB controlling these light fittings has tripped again since you have replaced the fittings?? If so have you tested anything at all before coming here asking for advice, if so what tests have you performed, and what values did you obtain??

 

[HandySparks]

What current is being supplied via this breaker?

 

[newsparky]

Could be a faulty MCB. Might be worth visually inspecting all the lights also. Remember rule number 1 though :

Always ignore what the client says and work it out for yourself.

All lights were inspected and fine apart from the ones I replaced.
I agree with possible MCB fault but seems strange why it only happens when I'm not on site!

 

[Leesparkykent]

My bet would be a dodgy ballast in one of the fittings,if all your test results are fine on the cabling.
disconnect one at a time and leave over night and see if it trips until you find dodgy one.

 

[ruston]

Could be a tenant switching it off because its shining in their window.

 

[Guest125]

All lights were inspected and fine apart from the ones I replaced.
I agree with possible MCB fault but seems strange why it only happens when I'm not on site!

Have you you checked the photocell and photocell circuit?

 

[newsparky]

Have you you checked the photocell and photocell circuit?

Circuit checked but not yet tested photocell.

 

[Guest125]

All lights were inspected and fine apart from the ones I replaced.
I agree with possible MCB fault but seems strange why it only happens when I'm not on site!

And internally. Looking at the ballasts and 'guts'?

 

[newsparky]

Thanks for your suggestions, will start with the photocell and ballasts and then MCB replacement if that fails.

 

[Guest125]

That is where I would go!

 

[davesparks]

What results did you get when you IR tested the circuit?
What results did you get when you IR tested the circuit after it had been on long enough to get up to working temperature?
Was there a difference between the two results?