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.

 

[davesparks]

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

Might I suggest carrying out testing of the circuit, including recreating the conditions in which the fault occurs. Rather than just replacing parts until you get the right one which is what you appear to be suggesting here.

 

[Guest125]

Might I suggest carrying out testing of the circuit, including recreating the conditions in which the fault occurs. Rather than just replacing parts until you get the right one which is what you appear to be suggesting here.

All I said is once you have tested everything and VISUALLY inspected the photocell and ballast and all appears ok try changing the MCB.

No one has said to keep changing parts until you fix it.

*removed*

 

[davesparks]

All I said is once you have tested everything and VISUALLY inspected the photocell and ballast and all appears ok try changing the MCB.

No one has said to keep changing parts until you fix it.

*removed*.

I am not lying, he did appear to be suggesting that he would be changing the photocell, then the ballasts and then if that doesn't fix it the mcb. It is plain to see in the post of his which I quoted in mine.

I did not categorically state that he

 

[Guest77]

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??

Don't be daft, that is just plain silly asking such a question, there is more chance of the moon producing snow.

 

[Leesparkykent]

If you read the previous posts you can clearly see what has been suggested is checking/testing and not replacing. So when the op states I will start with the photocell and ballasts it clear to see that he means check / test and not just replace them. If all else fails he will the replace the mcb.

 

[HandySparks]

What current is being supplied via this breaker?

Would be useful to know whether the normal current in the circuit is anywhere near overloading the circuit breaker.

 

[Octopus]

Would be useful to know whether the normal current in the circuit is anywhere near overloading the circuit breaker.

Me thinks you'll be waiting a while for the answers to that!

 

[davesparks]

If you read the previous posts you can clearly see what has been suggested is checking/testing and not replacing. So when the op states I will start with the photocell and ballasts it clear to see that he means check / test and not just replace them. If all else fails he will the replace the mcb.

And if that still doesn't fix it?

What if it turns out to be that the circuit is loaded up to its max and that extra bit of effort it takes to strike the lamps on the really cold evenings is what is causing this?

 

[Guest125]

And if that still doesn't fix it?

What if it turns out to be that the circuit is loaded up to its max and that extra bit of effort it takes to strike the lamps on the really cold evenings is what is causing this?

Then the C type MCB should deal with that.

 

[davesparks]

Then the C type MCB should deal with that.

What I mean is that if the inrush is already nearly at the tripping threshold then the extra required to strike the lamps when it's very cold could push it over.

 

[Leesparkykent]

And if that still doesn't fix it?

What if it turns out to be that the circuit is loaded up to its max and that extra bit of effort it takes to strike the lamps on the really cold evenings is what is causing this?

because the information i have given is from what is in the OP, lights switch off over night so from this i gather the lights have already started and are on and at some point during the night the lights trip.

 

[Guest125]

What I mean is that if the inrush is already nearly at the tripping threshold then the extra required to strike the lamps when it's very cold could push it over.

Yes but that is what a C type is designed to do. Absorb the higher demand of a circuit when starting up such as fluorescent lights and sodium/MH lamps.

 

[davesparks]

Yes but that is what a C type is designed to do. Absorb the higher demand of a circuit when starting up such as fluorescent lights and sodium/MH lamps.

No it isn't, it doesn't absorb anything!

A C type mcb is designed to allow inrush currents up to a certain multiplier of it's rated current to flow without causing operation. If the circuit's inrush is already close to that level then any extra may well cause operation.

 

[Guest125]

No it isn't, it doesn't absorb anything!

A C type mcb is designed to allow inrush currents up to a certain multiplier of it's rated current to flow without causing operation. If the circuit's inrush is already close to that level then any extra may well cause operation.

Sorry for my layman's terms but in effect that is what happens.

 

[davesparks]

Sorry for my layman's terms but in effect that is what happens.

No it isn't, if it absorbed the current then the lamps wouldn't strike!