mccb tripping

[pevvers]

A faulty MCCB by any chance?

I can't think of many other things, as a 125A MCCB even set to 0.6 on the thermal setting would still be 75A to trip, and you're obviously not getting anything like that....

Have you tried a data logger or current clamp with a peak hold setting to see whether there is anything untowards?

 

[lj.l]

Well got it sorted, after I'd tested all the submains and swapped the mccb with another one .
I stripped the covers of the main busbars that run up the board , which the busbars to the mccbs are bolted .The one for L3 was sitting loose and was overheating ,heating up the mccb and tripping it,few turns and that was it.
Probably havent explained it to well should have took a foto .
Thanks for all the replies guys appreciate it !
sometimes its the really simply things that seam the hardest to find.

 

[pevvers]

Now that would have been a job for a thermal imager if there ever was one, it would have stuck out like a sore thumb!!

 

[lj.l]

too right ,would definetly have saved a lot of head scratching and assuming.
Also a good idea to use a camera when doing any work on a old installation or a pir, would give a fuller picture of what you are getting into.never before thought that I would have a use for one .might invest.

 

[pevvers]

Definitely worth the money. I was looking at a few yesterday, and if you want a decent quality camera without all the snazzy bits like visible light image fusion, then you can get a Flir i5 for just over 2 grand.

I think it's the way forward, and if you've got PIRs on commercial properties to do, a thermal imager will maybe pick up on some stuff you haven't seen, and also looks very good in the report...