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.