Breaker tripping with no load?

[fxstbi]

Long time lurker with a question. I'm finishing my shop building and doing some outlet installation. I have a 100 amp service brought into the shop by an electrician, the breaker I'm using is a GE 15 amp. I had asked for a 20 but this is what he installed. I have a 70 foot run with four junction boxes that each have about a ten foot drop to an outlet. It's a metal building so I used MC 12/2 so I could have 20 amps available. My dilemma occurred when I finished wiring and turned on the breaker. There was nothing plugged in that circuit but the breaker tripped in about five minutes, I tried it several times and it tripped ever time. I then opened my first junction box about 20 feet away, unhooked all the wires, put wire nuts on the "hot" wires and tried the breaker again. No tripping?!? Any thoughts about what the problem would be? Do I have too much resistance from the 12/2 wire and the overall length? The electrician that did the primary work is out of town until next weekend or I would lean on him. Any help would be appreciated, thanks.

 

[spike99250]

Weren't there wire nuts on them before you opened them up?

 

[BillK]

Sorry, I misread the original post and the part where you disconnected the wires and the problem went away. Like Wily said, sounds like something past that point is causing the problem.

 

[wyliesdiesels]

Since u undid the splices at the first box and no trip, it is likely an issue downstream of that.

 

[fxstbi]

Thanks for the replies. I thought I was very through, any thoughts on what in particular I should be looking for? I'll go through every joint again. What's puzzling is that it trips after a few minutes of no load.

 

[matt_i]

There's probably light contact hot to a ground wire somewhere, where it got stuffed into the box haphazardly, its a little arcey connection that's just leaking enough current to get hot and trip after some time.

I did a similar thing by mistake, except ground lightly touching neutral screw which did not trip a breaker but would not allow the GFI outlet to reset.

I'd pull all of the cover plates and look carefully at the screws on the sides closeup to see issues. If you find none then have to pull outlets one at a time, or pull one and terminate in the middle of the run to see which way to work from there.

 

[walrus]

Got an amprobe? Measure the load. How'd you cut the mc?

 

[larry_g]

You really need a meter to measure the amp draw at the breaker box and a ohm meter to check resistance if there is an amp draw on the circuit with no load on it. Opening the one box could mean problems downline or in that box. Look for compromised insulation on the wires where ever you can see it.

Good trouble shooting practice is to start in the MIDDLE of the circuit to eliminate 1/2 the circuit at a time. If you break in the middle and the problem still exists then go 1/2 way back and break again. If you break in the middle and the problem goes away then reconnect and go 1/2 way to the end and break again.

lg
no neat sig line

 

[tvtaurus]

Only 2 possibilities here. Defective breaker or a short in the wiring. All electrical problems can be summed up into one of 3 problems.

Electrical problems:
* Shorts
* Opens
* High Resistance

 

[H-D Dad]

You really need a meter to measure the amp draw at the breaker box and a ohm meter to check resistance if there is an amp draw on the circuit with no load on it. Opening the one box could mean problems downline or in that box. Look for compromised insulation on the wires where ever you can see it.

Good trouble shooting practice is to start in the MIDDLE of the circuit to eliminate 1/2 the circuit at a time. If you break in the middle and the problem still exists then go 1/2 way back and break again. If you break in the middle and the problem goes away then reconnect and go 1/2 way to the end and break again.

lg
no neat sig line

Excellent troubleshooting practice.

 

[fxstbi]

Good information, thanks again. I'll put first junction box back together carefully and start checking the rest of them and the outlets. I'll post my results.

 

[happy2rv]

If you are using armored cable, did you use the plastic anti short bushings at every connection? They aren't necessarily required by NEC, but I've seen way too many connections where armored cable gets clamped in without one and the cladding nicks the insulation causing a short.


http://www.homedepot.com/p/3-8-in-Flexible-Metal-Conduit-FMC-Anti-Short-Bushing-35-Pack-75401/100170558

 

[fxstbi]

Walrus, I apologize I didn't answer your question. I did the sharp bend method and carefully cut the metal cover where it split. I did use the plastic bushing and made sure the tail was visible. When I cut the armor I checked the wires to be sue nothing was nicked.

 

[klassenl]

Only 2 possibilities here. Defective breaker or a short in the wiring. All electrical problems can be summed up into one of 3 problems.

Electrical problems:
* Shorts
* Opens
* High Resistance

Can you elaborate on these 3 points.

 

[wyliesdiesels]

Only 2 possibilities here. Defective breaker or a short in the wiring. All electrical problems can be summed up into one of 3 problems.

Electrical problems:
* Shorts
* Opens
* High Resistance

Can you elaborate on these 3 points.

A short would trip the breaker.

An open or broken wire would not.

A high resistant splice MAY cause the breaker to trip if it causes an overcurrent condition on the circuit. However most high resistant connections end up burning themselves out.

 

[walrus]

With no load I don't see how high resistance is causing this issue.

 

[Dagny]

You can't keep turning it on to find it your going to start a fire . Get an ohm meter and use it as a power source. then do the half way troubleshooting.

 

[Dagny]

If an ohm meter don't show any conductivity you need to use a megger.

 

[fxstbi]

Success, I found one bundle of wires that had a loose wire when I pulled on it. I corrected that and finished checking everything else. I turned on the breaker and it's staying on. I had no idea that a loose wire could cause that kind of problem. Thanks everyone for the replies!

 

[justsam]

A loose wire in a single bundle, say a bundle of hot wires, or a bundle of neutrals would not normally trip an over current breaker, unless that somehow facilitated a hot wire touching a neutral or ground. Was this a simple over current breaker, or was it possibly an AFCI, or GFCI breaker?

 

[rburke65]

Nice work! You are now officially an Electrician Apprentice!

 

[wyliesdiesels]

With no load I don't see how high resistance is causing this issue.

forgot to put that on my last bullet point. thank u

A loose wire in a single bundle, say a bundle of hot wires, or a bundle of neutrals would not normally trip an over current breaker, unless that somehow facilitated a hot wire touching a neutral or ground. Was this a simple over current breaker, or was it possibly an AFCI, or GFCI breaker?

Exactly.

A regular breaker wouldnt care about loose wires that are part of the same bundle.

A GFCI wouldnt care about loose wires in the same bundle either. It would only care about a neutral to ground connection.

An AFCI WILL care about loose wires in the same bundle IF there was current flowing through the splice and there was arcing as a result of the loose connection.

OP is this a regular breaker? or is it a GFCI or AFCI or both?

 

[BLUE72CAMARO]

If you are using armored cable, did you use the plastic anti short bushings at every connection? They aren't necessarily required by NEC, but I've seen way too many connections where armored cable gets clamped in without one and the cladding nicks the insulation causing a short.


http://www.homedepot.com/p/3-8-in-Flexible-Metal-Conduit-FMC-Anti-Short-Bushing-35-Pack-75401/100170558

Wish I had known about those two weeks ago! I had this issue when installing the ceiling fans in my shop and took about an hour to find the problem and fix it.

 

[fxstbi]

Well I'm embarrassed to say my breaker tripping (regular breaker by the way) was still an issue, evidently I didn't wait long enough for it to trip the last time I was in the shop. So this time I jumped into the middle of the circuit and disconnected wires at the junction box and kept trying the breaker to see if it kicked out until I found the problem section of wire. I triple checked to make sure I had it isolated and then pulled it down to find the culprit wire. I found a slight nick in the black wire right at the joint of the metal cover. It looks like it could have happened when I folded the cable over in a sharp bend to expose the wires. I was too cheap to buy the 35.00 tool to cut the armor so it caused me many hours of work to find the problem, stupidity got the upper hand this time! I have more wiring to do so I WILL be buying the proper tool for the job. Thank you all for taking the time to post, it's very much appreciated.

 

[wyliesdiesels]

Yeah bending armored cable like that is not a good idea.

I use the Ideal sir nickless cable cutter.

http://m.homedepot.com/p/Ideal-Sir-Nickless-Armored-Cable-Cutter-35-782/203761573

It has a curve in the tray that naturally forces the conductors away from the cutting blade.

And it makes sense that it didnt cause an instant trip as there wasnt enough current flow.

 

[teamextreme]

Ya, cutting AC without the right cutter is risky at best. I've heard of inspectors that check to make sure the right tool was used for this. At the risk of being a Monday morning quarterback, my money was on that as being the issue as soon as I read how you cut it.

 

[sberry]

I think its great the op kept with it, followed some basic investigation and finally got to the root of the problem. I am a little curious why the gfci didn't trip although I don't recall all the details to the thread but the breaker and the grounding system did just what it was sposed to do.

 

[tvtaurus]

Success, I found one bundle of wires that had a loose wire when I pulled on it. I corrected that and finished checking everything else. I turned on the breaker and it's staying on. I had no idea that a loose wire could cause that kind of problem. Thanks everyone for the replies!

A loose wire equals high resistance/arcing.

 

[wyliesdiesels]

A loose wire equals high resistance/arcing.

Yes that us true. But for that to cause a breaker trip would require current to be flowing which there was none since there wasnt anything plugged in.

 

[FreddiFiche]

Excellent troubleshooting practice.

Divide and Conquer!

 

[gnxtc2]

Ya, cutting AC without the right cutter is risky at best. I've heard of inspectors that check to make sure the right tool was used for this. At the risk of being a Monday morning quarterback, my money was on that as being the issue as soon as I read how you cut it.

We had a local inspector that would fail jobs on the type of crimper used on ground barrels. You had to be present on the job when he inspected. If you used ground barrels, he asked to see the crimper. If Ideal ground barrels were used, he wanted an Ideal Crimper. If you used the Klein crimper on Buchanan barrels, he failed the job. Needless to say, all the contractors called up the Board of Electrical Inspectors complaining about him.

When I started working as an electrician (over 25 years ago), I worked for this old timer and tyrant. The only tools we were allowed to use were the one approved by him. He used only steel BX (no aluminum jacket), RMC (galv and aluminum) and metal boxes. And we did new residential construction. If a builder wanted him to use RX/plastic boxes, he wouldn't do the job.

Getting back to the BX. We were only allowed to use a hacksaw to cut the BX. If we bought a Roto-Strip BX cutter, we were told to get rid of it. He wanted things done his way and only his way. We weren't allowed to use cordless tools either. All screws were installed by manual labor.

Needless to say, I didn't last too long.

Billy T.
[email protected]

 

[wyliesdiesels]

We had a local inspector that would fail jobs on the type of crimper used on ground barrels. You had to be present on the job when he inspected. If you used ground barrels, he asked to see the crimper. If Ideal ground barrels were used, he wanted an Ideal Crimper. If you used the Klein crimper on Buchanan barrels, he failed the job. Needless to say, all the contractors called up the Board of Electrical Inspectors complaining about him.

When I started working as an electrician (over 25 years ago), I worked for this old timer and tyrant. The only tools we were allowed to use were the one approved by him. He used only steel BX (no aluminum jacket), RMC (galv and aluminum) and metal boxes. And we did new residential construction. If a builder wanted him to use RX/plastic boxes, he wouldn't do the job.

Getting back to the BX. We were only allowed to use a hacksaw to cut the BX. If we bought a Roto-Strip BX cutter, we were told to get rid of it. He wanted things done his way and only his way. We weren't allowed to use cordless tools either. All screws were installed by manual labor.

Needless to say, I didn't last too long.

Billy T.
[email protected]

Geez. What an old shrew. He shouldve retired.

Im surprised he didnt realize how much labor time he could save by using cordless tools and the right roto cutter. I have the ideal sir nickless model. In the future im gonna by one of the large BX cutters made by roto.

I wouldnt have lasted long either with that guy.

I worked for a union electrician one time that did a very bad job at following codes that i wont go into. I was shocked. I left after 4 months for a better employer.

 

[walrus]

Well I'm embarrassed to say my breaker tripping (regular breaker by the way) was still an issue, evidently I didn't wait long enough for it to trip the last time I was in the shop. So this time I jumped into the middle of the circuit and disconnected wires at the junction box and kept trying the breaker to see if it kicked out until I found the problem section of wire. I triple checked to make sure I had it isolated and then pulled it down to find the culprit wire. I found a slight nick in the black wire right at the joint of the metal cover. It looks like it could have happened when I folded the cable over in a sharp bend to expose the wires. I was too cheap to buy the 35.00 tool to cut the armor so it caused me many hours of work to find the problem, stupidity got the upper hand this time! I have more wiring to do so I WILL be buying the proper tool for the job. Thank you all for taking the time to post, it's very much appreciated.

That's why I asked you how you cut it. Glad you found your problem. This is a tool site now go buy the right tool

 

[LS6 Tommy]

We had a local inspector that would fail jobs on the type of crimper used on ground barrels. You had to be present on the job when he inspected. If you used ground barrels, he asked to see the crimper. If Ideal ground barrels were used, he wanted an Ideal Crimper. If you used the Klein crimper on Buchanan barrels, he failed the job. Needless to say, all the contractors called up the Board of Electrical Inspectors complaining about him.

Billy T.
[email protected]

Shouldn't he have failed you no matter brand of barrel or crimpers you used? Last time I checked, crimp connectors aren't supposed to be used with solid wire. IDK if it's a code violation to do so. dunno:

Please correct me if I'm wrong

Tommy