ECN Forum Forums General Topics of the Trade General Discussion Area one tripping another

Last job I was on there was a strange deal.

I'll break down the facts:

Lighting ckt:#31
Power:#6

I was working on the lighting so I went to the panel to turn off ckt 31. I went back the the jb with ckt 31 and it was off.

Then, another electrician had to turn it on during lunchtime for these bigwigs having a meeting in a room on CKt 31. I came back after lunch and noticed that it was tripped.

Here is what is wierd. When I reset ckt 31, it tripped along with ckt 6 (power) . I did not do the roughf in . But, what could possible cause this. The GF did not have any clue either. He took over the job half way through.

Both ckts are in the same panel 6 and 31. Any ideas? Even if there is a ground fault on the lighting circuit I was working on , how would 6 trip as well?

A ground fault on one of the circuits should not have caused the other one to trip. Are you sure #6 was on when you turned off #31? Maybe the two got tied together somewhere down the line. Since #6 would be on "C" and #31 would be on "A" this would cause one or both of the breakers to trip. When the other electrician turned on #31 he may have also turned on #6. Did you check to see if the lights work if either on of these breakers were on? Just a thought. Good luck!

Eandrew
If there are any 3way switches on the lighting circuit, the use of a different circuits grounded conductor could be the cause. I have seen two breakers trip because the grounded conductor of a different circuit was used to eliminate the need to run one along with the travelers from 3ways. When this is done a short to ground will trip two breakers. It also makes it tough to put a ground fault receptacle in either circuit.

Sounds like you have two circuits running into each other someplace - either by switchlegs as described by a member, or a makeup mistake in a J-Box.

If the system is 3 phase, that puts Ckt. 6 on phase C and Ckt 31 on phase A.

One other place to find the fault location would be inside light fixtures where bilevel or "a/b" switching is used.
Have found this to be the most common makeup mistake when breakers trip as you have described.
Finding the person that did the makeup is difficult on large jobs [so you can explain the mistake and why it needs to be avoided, not to do any finger pointing or put downs]. Typically it's a Helper that is under pressure, or a Journeyman having a bad day.

From your description it sure sounds like the two circuits got tied together someplace by mistake. If I am correct, you could leave one of the breakers off, turn the other on and nothing pops. You will also read voltage at the load terminal of the breaker that's in the off position.
The real problem lies in finding where the mistake is at without opening too many things. Correcting it is simple.

If the system is 277/480 and the main service is 1000 amps or higher, you would know if this was a ground fault. The main would trip! [GFPE type main].

Let us know of the outcome.

Scott S.E.T.

I left this job without find out what the problem was. Scott, it had to be a mistake the makeup like you say.

Eandrew

What about me? I said the same thing as Scott but 3 days earlier. Why does he get all the credit?

Have a great weekend!

Curt