Main breaker tripping problem

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hbdocm

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Hello everyone,

I have a customer that states they had a "electrician" do some work for them and soon after they had main breaker problems. I took a look and whenever I reset one of 2 different breakers it trips the main breaker of the panel otherwise the panel works fine. I left these breakers off and need to return this weekend to try and troubleshoot. Does anyone have any idea what would cause a main to trip when turning on a 20A circuit?? The only thing I could think of was possibly the electrician tied L1 and L2 together in a J-box somewhere causing it to bond the busbar together???? I don't believe a dead short on a 20A circuit would be enough to throw a 100A main but have seen it on higher amperage circuits. Any help on this would be much appreciated!
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
If the two phases are together on the 20s I don't think it is that unusaul for a 100 amp main to trip.
 
kbsparky

kbsparky

Senior Member
Location
Delmarva, USA
A dead-shorted 20 Amp circuit can easily trip out a 100 Amp main. I've seen this trip a 200 Amp main, if there is sufficient available fault-current. In cases where a high amount of fault current is present (sometimes called "let-thru") the breakers -- including the main -- can have sufficient explosive effect so as to appear to jump right off the buss bars!

Do they trip if either 20 Amp circuit is switched on? Or, only when both of those branch circuits are turned on at the same time?
 
H

hbdocm

Member
Main breaker tripping response

Main breaker tripping response

My employee was the one that went out to test and it was late so he disabled the 2 breakers and got them back up and running. He has not tested voltage on the load side of the breakers and he said if either of the 2 breakers was turned on it would trip the main breaker. They are (2) single pole 20A breakers and are NOT a double pole 20A. It started to occur soon after they had some electrical work done so I was thinking a short might be the most likely problem. This is the first time I have seen a short on a 20A circuit take out a main however.
 
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