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#48560 - 02/15/05 04:17 PM distribution breaker trips branch circuit doesn't  
cvelectric  Offline
Joined: Apr 2004
Posts: 30
This is something I haven't seen before and am not sure how to handle. A warehouse has a 600a or 800a distribution panel (not sure which) feeding a 125a, 3-phase, 208v. branch circuit panel. When they plug in a small space heater in an office,the 125a main in the dist.pnl. trips after about 10 minutes,(the 20 a. breaker for the office cir. and the 125a. main in the branch cir. panel do not trip). The load on the cir. is 12a. with the heater going and there is very little load on the 125a. breaker (like 40a. on C ph.). The dist.pnl. is a GE Spectra series,the branch pnl. is square D QO. The breaker has the adjustable trip aic and I've gotten prices ranging from $1000 to $1900 for it. I don't want to just replace the breaker and find out that is not the problem. Thanks.

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#48561 - 02/15/05 07:50 PM Re: distribution breaker trips branch circuit doesn't  
livetoride  Offline
Joined: Jan 2005
Posts: 109
san diego ca usa
I had an emergency call at a large office building, dark and stormy night, The main was tripped. I turned off all the breakers and reset the 2000 Amp (I think) main. Then turned on each breaker one at a time till it tripped again. I got everything on except the one 200amp panel. Turned out an A/C unit had a ground fault. Check the heater. Good luck Rod

#48562 - 02/15/05 08:10 PM Re: distribution breaker trips branch circuit doesn't  
Tom  Offline
Joined: Jan 2001
Posts: 1,044
Shinnston, WV USA
Another thing to check for is loose connections at the breaker, including the connection to the distribution busbar. Heat from a loose connection can trip a breaker.

If you find no loose connections, listen for sizzling or crackling sounds in the breaker which would indicate internal connections going bad. Try placing the tip of a large screwdriver against the breaker case & then place your ear against the end.


Few things are harder to put up with than the annoyance of a good example.

#48563 - 02/15/05 08:15 PM Re: distribution breaker trips branch circuit doesn't  
resqcapt19  Offline
Joined: Nov 2000
Posts: 2,148
The GE Spectra series of breakers has a plug in trip unit. If that is missing or not functional, the breaker will trip at about 10% of the handle rating.


#48564 - 02/16/05 09:33 AM Re: distribution breaker trips branch circuit doesn't  
cvelectric  Offline
Joined: Apr 2004
Posts: 30
Thanks for the replies. I did not suspect a short in the heater since it worked fine when plugged in to a circuit fed from a different panel but maybe a low level short? I will definately check for a loose connection today. Don thanks for the link--very helpful I could not find it on GEs website yesterday. The trip unit plug sounds like a good place to start ($106).

#48565 - 02/17/05 09:35 PM Re: distribution breaker trips branch circuit doesn't  
sierra electrician  Offline
Joined: Feb 2005
Posts: 219
North Fork, CA USA
The last time I saw this was a service that was within 25 feet of the Utility Co transformer. The AIC rating was so high that short in a 20A circuit would trip the main even with the adjustable main overload cranked.


#48566 - 02/18/05 11:15 AM Re: distribution breaker trips branch circuit doesn't  
JBD  Offline
Joined: Jul 2001
Posts: 599
The AIC (amps interrupting capability)rating of a device has nothing to due with it's trip curve. However, the available short circuit amps (SCA) does affect the amount of fault current that flows which may cause upstream devices to operate.

I agree with the comments about the trip unit rather than the entire breaker.

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