Main breaker trip

[rickkurtzuba]

Siemens 100 amp panel. Whoever installed did not label circuits. Feeds an apartment. Everything in the apartment works. Building has original knob and tube and two sets of Romex installed during past renovations. Guy who cleans noticed a breaker was tripped. He flipped it and immediately the main tripped. We haven't traced that circuit, no clue what the breaker is protecting as there are no outages in the apartment. My guess is a short maybe created by a nail or screw. Confusing me is that nothing in the apartment is dead with that breaker off, and that flipping the breaker doesn't only trip that breaker, but the main as well.

 

[Little Bill]

Please don't turn that breaker back on that is tripped. You have a definite short somewhere and it needs to either be repaired or disconnected. I would suggest you get an electrician to check this out.

We can't really give any "how to " advice since you are not an electrician.
All members, no "how to" replies please.

 

[petersonra]

Siemens 100 amp panel. Whoever installed did not label circuits. Feeds an apartment. Everything in the apartment works. Building has original knob and tube and two sets of Romex installed during past renovations. Guy who cleans noticed a breaker was tripped. He flipped it and immediately the main tripped. We haven't traced that circuit, no clue what the breaker is protecting as there are no outages in the apartment. My guess is a short maybe created by a nail or screw. Confusing me is that nothing in the apartment is dead with that breaker off, and that flipping the breaker doesn't only trip that breaker, but the main as well.

There might be something dead that isn't real obvious like a ventilation fan or some outlets that aren't currently in use.

Your best bet is to find a decent electrician and have him figure out what's going on.

It's also possible the circuit breaker feeds something in another apartment. Who knows.

 

[James L]

Confusing me is that nothing in the apartment is dead with that breaker off, and that flipping the breaker doesn't only trip that breaker, but the main as well.

I can think of a couple of scenarios where a circuit might not be obvious.

As for tripping a 100 amp breaker, that's not surprising with a dead short.

Call an electrician who knows old apartments

 

[ptonsparky]

Call an electrician.
If they turn the breaker on without preliminary investigation...get a different one.

 

[augie47]

Save a few $$ troubleshooting Have the electrician disconnect the load side to prevent a reoccurance and wait and see if something doesn't work.

 

[ptonsparky]

Save a few $$ troubleshooting Have the electrician disconnect the load side to prevent a reoccurance and wait and see if something doesn't work.

We did that more than once on rewires where we could not find the load to identify the circuit. Generally no one ever called back.

 

[Jraef]

As a pure guess from my experience owning a 100+ year old house that had been wired with knob and tube, it is likely a circuit that someone had abandoned inside of the wall during a remodel, but improperly. So rather than try to figure it out, which can be difficult with K&T wiring, a previous owner just turned off the breaker and left it off, then re-wired whatever didn’t work, which might be the romex that you see now.

But yeah, this needs the attention of an experienced licensed electrician to confirm that it is not needed, AND to properly abandon the circuit if that’s the case.

 

[Jraef]

…
It's also possible the circuit breaker feeds something in another apartment. Who knows.

That’s been the plot of countless comedy routines, going back as far as the beginnings of having electricity in houses, all the way up to a classic “Friends” episode. It undoubtedly stems from realities that comedy writers encountered.

In my house there's this light switch that doesn't do anything. Every so often I would flick it on and off just to check. Yesterday, I got a call from a woman in Madagascar. She said, 'Cut it out.'

Steven Wright

 

[qcroanoke]

I can think of a couple of scenarios where a circuit might not be obvious.

As for tripping a 100 amp breaker, that's not surprising with a dead short.

Call an electrician who knows old apartments

Wonder if it's bucking phases when they turn that circuit on because it's double fed from both phases?

 

[ptonsparky]

I had a customer with a non-compliant rental. The basement apt lost all lighting. Yup, the single pole switch at the top of the stairs. I'm sure the main floor renters wondered what it was for.

 

[qcroanoke]

There might be something dead that isn't real obvious like a ventilation fan

I found that once. Breaker would trip instantly. Finally looked in attic and there was a vent fan. I unhooked it and problem went away.

 

[James L]

Wonder if it's bucking phases when they turn that circuit on because it's double fed from both phases?

Could be. I just finished wiring an attic loft.
Somebody else decided to help by running some circuits begore subfloor was installed. He had crap run everywhere that didn'tgo to anything. Some hot, some not.

One circuit was just laying on the floor, and I wanted to find out what was on it. I dead-shorted it (in such a way that it didn't arc), and it tripped a single pole 20 amp breaker in a subpanel as well as the 100 amp breaker which feeds that subpanel.

 

[jaggedben]

Could be. I just finished wiring an attic loft.
Somebody else decided to help by running some circuits begore subfloor was installed. He had crap run everywhere that didn'tgo to anything. Some hot, some not.

One circuit was just laying on the floor, and I wanted to find out what was on it. I dead-shorted it (in such a way that it didn't arc), and it tripped a single pole 20 amp breaker in a subpanel as well as the 100 amp breaker which feeds that subpanel.

It boggles my mind how irresponsible some people can be in this manner. Had a situation not unlike that in a basement with a hot dangling romex that arced against a water pipe when I bumped it. Why would you hook up a wire to a breaker if you don't know what's on the other end?

The general lesson here. If something is tripped, or off, or not hooked up, and no one is complaining about something not working ... don't hook it up or turn it on!

 

[James L]

Why would you hook up a wire to a breaker if you don't know what's on the other end?

The person who came before me had it energized already. It ended up being a home run connected to nothing, just laying on the floor

 

[ammklq143]

I'd check for power on the load side of the tripped breaker and see if it's backfed. If so, start turning other breakers off until it's dead to see what circuit it is. I replaced a fuse box in an old house and when I landed all of the wires back in the new panel and turned the breakers on, one breaker would immediately trip but everything still worked. Whoever wired the house wired a kitchen receptacle circuit with two feeds so it was being fed from each direction. Pulled a receptacle in the middle of the circuit and disconnected one of the feeds and everything was fine.

 

[ptonsparky]

I'd check for power on the load side of the tripped breaker and see if it's backfed. If so, start turning other breakers off until it's dead to see what circuit it is. I replaced a fuse box in an old house and when I landed all of the wires back in the new panel and turned the breakers on, one breaker would immediately trip but everything still worked. Whoever wired the house wired a kitchen receptacle circuit with two feeds so it was being fed from each direction. Pulled a receptacle in the middle of the circuit and disconnected one of the feeds and everything was fine.

Been there.

 

[drcampbell]

One likely reason the main breaker trips when that branch breaker is turned on
is that the branch breaker is defective, no longer responds to overcurrent,
and is now functioning only as a switch.

There may be more than one fault to address.

 

[kwired]

Wonder if it's bucking phases when they turn that circuit on because it's double fed from both phases?

Had OP's situation one time and that is what it ended up being. Two circuits leaving panel opposite legs, but got tied together in a lighting outlet. Was older home and was original wiring and had been that way for years before I discovered it.

 

[Jraef]

I found that once. Breaker would trip instantly. Finally looked in attic and there was a vent fan. I unhooked it and problem went away.

I have an attic vent fan for summer, controlled by a switch in my family room. My sister did some house sitting for us one year when we had Christmas in Hawaii, she called me telling me there was a strange vibration in the family room. I asked if she had flipped that switch On, she said yes, but it didn’t do anything… she wasn’t correlating the switch with the vibration.