mccb tripping

[lj.l]

Does anyone have any Ideas why a 125A mccb would trip?
Been called out today twice to same job 1st time I reset it and no problems ,but then it went again this evening .
It's not overloaded ,I didnt do any IR tests as I couldnt gain access to the bar It was suppling just the office.
My first thoughts were a damaged sub main but I cant think were as there has been no major work there for a month .
I did notice the mccb was very warm but there were no loose conections.
I know what I have to do to find whats wrong but am looking for ideas to help speed things up.
Thanks in advance.

 

[pennywise]

Did you put a clamp meter on it once you reset it to see what the load was?

 

[Johno]

is it protecting the main board or is it a separate isolator for a sub main

 

[lj.l]

yip
L1 -11a
L2 -25a
L3 -30a

Phases are a bit unballanced but thats another issue this has been running like this since it was done 4 years ago.

 

[pennywise]

So does the bar have a kitchen?

 

[lj.l]

Its a damm funny set up .The mccb is in a panel board and feeds through a meter to a set of iscos from which there are 3 switchfuses feeding sub boards.
One db for the office another for the bar and another for the niteclub.
I havent been there to check the full load when the bar and niteclub are both in operation but the mccb is tripping when there is virtualy no load on it which to me seams like a damaged sub main.
Have any of you had a problem like this and it turned out to be a circuit of one of the sub boards?
I cant see this really happening as the mcb/rcbo should be protecting its own circuit!

It has a kitchen ,as far as I know its all gas. Bar wasnt even open today so only thing running is fridges and stuff,there would be dishwashers and glass washers but the wouldnt have been running today.

 

[Johno]

sorry, whats a panel board that feeds through a meter. i cant get a picture of what you mean

 

[pennywise]

If it had been a fault that was occurring on one of the circuits on the dis boards the individual breaker would have gone not a 125A mccb. It sounds like it could be an overload especially with the mccb running hot and bars and clubs are buggers for adding on stuff,or a lose connection at the dis boards in the club or bar, but as you say you'll find it pretty quickly, may even be a faulty mccb. Does the mccb have a thermal overload or short circuit setting .

 

[lj.l]

sorry mate .
A panel board that accepts mccbs, its just like a normal tp&n board only on a large scale and designed for mccbs.
the meter is seperate and fed from an mccb in the panel.
hope this describes it better ,thats the only name I know for It

 

[Johno]

i will leave this one to you two, goodnight

 

[SirKit Breaker]

Has it got a mechanical fault causing it to drop open as opposed to tripping?

 

[bugsy]

Check the discrimination on all the ocpd's , I had a simular problem a year ago, faulty overdoor heater protected by type d mcb.

 

[craig]

I had something similar a while back. It turned out to be the bars in the 3phase DB tracking and then clearing due to moisture build up in the kitchen through cooking steam ect. I found it eventually when the DB go bang, because everytime it was tested everything was clear and nothing to see.

Just an idea ?

 

[pennywise]

Like this.

[ame=http://www.youtube.com/watch?v=iyJy7JYe410]YouTube - MCCB ç￾«èŠ±[/ame]

 

[Notsosmart]

Not sure I would get so close to arcing busbars.

 

[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...