Lights tripping mcb when switched on

[Sav]

Hi everyone,
Hope your all ok and busy busy !!!

Just got back from a callout. Lady has had a chandelier type fitting just put up on her ceiling with 20 of those small 20w lamps inside it. Also she has had 4 new wall lights put on as well (100amps each, the kind of lamps that you fit onto the motion detectors, long type ).

Anyway, her builder switches on the lights and the mcb trips, reset it, all ok, switch on lights, fine, switch off and mcb trips again !!
I went to have a look, the board is a Square D type board, 3 phase (these are duplex flats in Canary Wharf, approx 10 years old ).

Just by chance I had 1 x B type 10amp and 1 x 16amp C type Square D breakers in the van. The board is all C type by the way. I put on the the B type 10amp, thinking about maybe a surge when the lights are switched on (especially the massive chandelier type one ), The lights come on fine, go to switch off, the mcb trips. Reset it, switch on the mcb trips. So I put i the 16amp C type and all is fine !! Switch on ok, switch off ok, switch on again ok (2 way switch).

Do you think, as do I, that its a surge thats causing this ??? Checked continuity of earth in lights and did R1 + R2, all ok, insulation resistance all ok ??
I think I may order her a 10amp C type mcb, as the 16 may be too high ??, but in the consumer unit, the wiring is 2.5mm?

Any suggestions or advise?
Thanks for reading and have a great week everyone,
Sav

 

[jon jordan]

change mcb to a c type mate i would just to try..jon

 

[shirlock]

If all that lighting circuit is 2.5 then the 16a breaker will be ok

 

[Amp David]

Wouldn't just stick a 16 amp in because its wired in 2.5. What about his Zs value?

 

[Sav]

Wouldn't just stick a 16 amp in because its wired in 2.5. What about his Zs value?

Hi David,
I put back original mcb, as just wanted to check if possible surge thats causing problem.
Going back on wednesday ( as she is a regular customer, I called in on the way to another job ), do another test and go from there.
I justwanted to know if this has happened before to anyone and what the outcome was.
Thanks again though for the heads up.
best regards,
Sav

 

[shirlock]

Wouldn't just stick a 16 amp in because its wired in 2.5. What about his Zs value?

As he said he's tested I would have thought that he would had checked this before stucking the 16a.

 

[lloyd1980]

sounds silly but has someone nicked the switchwire when screwing up these 'chandaleres' (sorry for spelling) , do an IR test with the light switch 'on' and see if a short,
other than that its time and materials my friend

 

[saabuldin]

is it tripping from the 2nd switch or the same switch you switched in on from. Try testing it with the 2nd switch on. could be short in the strapper.

As you changed from 10amp b type to a 16amp c type. It could be overload or surge. try a 16amp b type

 

[Sav]

is it tripping from the 2nd switch or the same switch you switched in on from. Try testing it with the 2nd switch on. could be short in the strapper.

As you put in bigger breaker c type. It could be overload or surge. try a 16amp b type

Hi,
was doing it from both switches. Previous light fitting was a pendant apparantly and that worked fine.
As mentioned before, I had a spare C type 16amp in the van and this worked fine, so if there was a short or nail etc, this would have tripped as well.
Will be going back on Wednesday and will carry out proper tests, as I will have more time as well.

 

[Deleted member 9648]

If it was a starting surge I cant see that the mcb would trip when switching off.....I had one once on a storage heater fan circuit which would switch on fine but would trip every single time when switched off!!.....500v IR tests showed nothing and it was only when 1000v was zapped across that we got a flicker of a reading.....Was eventually traced to a cable that the lad had clipped under the floor and had stuck the nail right through the cable.................since then when I get odd things like this and 500v IR is clear I always try 1000v,it's worked several times.

 

[saabuldin]

thanks for the tip wirepuller. very useful