# Touching ground wire to metal box trips breaker



## lmm (Jul 22, 2014)

I am adding additonal outlets in my garage (finished walls) and jumping off an existing outlet (plastic box inside wall).

I am using flex conduit and metal boxes to install 2 new outlets and a switch. in this order, outlet ---> switch ---> outlet.

With first new outlet i put a ground wire attached to an install screw and then pigtailed that wire to the 2 other grounds and added another wire which attaches to the outlet ground screw.

All boxes are metal.

The outlet works fine and checked with a 3 prong tester.

I then installed a switch. Capped off the white wires together and placed the 2 black wires on the switch. I did the same grounding technique used on the first box.

With switch off, no issues. As soon as I turned the switch on the breaker trips. I checked all the wiring and used electrical tape to make sure there were no wires touching each other or something else.

After many attempts to figure it out i removed the ground wire going to the box (attached to install screw). 

When I flipped the switch, the breaker did not trip. To further test, I reattached the ground wire to the screw and left it hanging free. Turned on the switch, and breaker did not trip. With the switch turned on, i then touched the box with the ground wire and breaker trips!!!

I then went and installed the last outlet. Grounded it the same way as the first outlet and when the switch is turned on the breaker trips. WHen I remove the ground wire to the box it works. 

I put the 3 prong tester on the last outlet and i get a normal signal.

There were some electricians doing an install into a new home next door. They stopped by and took a quick look. Their first assumption is that the box was now hot. They did some wire testing and all the tests showed normal. Without further investigation they could not give me an answer.

Aren't all metal boxes supposed to be grounded? Did i do the grounding wrong? Or does grounding the first box in the line take care of all the other boxes.

Outlets are working fine right now.

Any helps, comments or diagnosis would be appreciated.


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## mpoulton (Jul 23, 2009)

The breaker and the grounding conductor are doing their job - tripping the breaker to eliminate the danger of a ground fault. This is not a complicated enough wiring scenario that it should be hard to troubleshoot. That metal box is hot due to a ground fault. It could be a scraped or pinched wire, a hot screw touching the box, a ground wire touching a hot screw, or any number of other possibilities. But it's not tough to sort out. Take that box apart, inspect, reassemble, and test. A multimeter reading continuity will help.


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## lmm (Jul 22, 2014)

How would I test continuity. I have a fluke digital multimeter. Just not sure how to find the ground fault.


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## Kpack (Aug 4, 2012)

Sounds like the breaker is working good now to find the short. :thumbup:


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## Daniel Holzman (Mar 10, 2009)

Based on your description, it sounds like the metal box(es) are energized. You can easily check this with a voltmeter, just put the red probe on the metal box, and the black probe on a ground wire, and see what voltage you read. My guess is you have a hot wire touching a metal box, thus energizing the box, but the box is not grounded, so until you touch the ground wire to the box, there is no current flow. Ground the box and you trip the breaker, since you complete the circuit.


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## HouseHelper (Mar 20, 2007)

How did you cut the flex conduit? My guess is you nicked the hot wire when cutting causing a fault to ground.


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## lmm (Jul 22, 2014)

I bent the flex and used wire cutter pliers to cut away the conduit. There might have been sharp edges and I clamped the rings pretty tight too.


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## lmm (Jul 22, 2014)

assuming I did nick a hot wire that's in the conduit. 

how does one fix that. do I need to replace the whole string of cable??


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## BigJimmy (Jun 30, 2006)

lmm said:


> assuming I did nick a hot wire that's in the conduit.
> 
> how does one fix that. do I need to replace the whole string of cable??


If you're going to do any cutting of MC cable in the future, the tool below is what you should be using. It will cut the armor without damaging the wiring. Also make sure that you use anti-short bushings at the cut ends of the cable. Finally, run the bonding wire through the anti-short, bend it back onto and wrap it around the cable armor.

If you have enough slack in the cable, you should be able to cut a short piece of the armor off (properly!) and inspect the insulation. Apply some heat shrink tubing over any compromised insulation.


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## Focused2 (Jan 2, 2013)

Check your connectors as well we seem to want to drive in screws with drill drivers and the screw on one of the connectors may have pierced a wire?
-
Food for thought, Joe


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## lmm (Jul 22, 2014)

I am using MC armored cable. I also did not use any bushing at the end of the cable. Completely missed that.

If I find the nick and put shrink tubing on it, that will meet code?? Is there special shrink tubing or any kind will do??

thanks for all the suggestions....


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## BigJimmy (Jun 30, 2006)

lmm said:


> I am using MC armored cable. I also did not use any bushing at the end of the cable. Completely missed that.
> 
> thanks for all the suggestions....


Definitely need to install anti-shorts in the open ends of all pieces of MC cable. You can buy them at the big-box stores and they're not expensive. They look like small red thimbles with a cut through their length. You push them into the cable between the wires and the armor. As I said, bring the aluminum bonding wire out of the mouth of the anti-short, wrap the wire over it (along the length of the armor) and then wrap it around the armor. The bonding wire will keep the anti-short from working its way out.

I always use a BX/MC cutter unless I am really in a pinch. When I forgo use of the correct tool, I carefully cut away all of the sharp edges and inspect the wire insulation before terminating.


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## Stubbie (Jan 7, 2007)

The switched power is the cable with your ground fault. Look at the cable carrying your switched power.


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## lmm (Jul 22, 2014)

BigJimmy said:


> . As I said, bring the aluminum bonding wire out of the mouth of the anti-short, wrap the wire over it (along the length of the armor) and then wrap it around the armor. The bonding wire will keep the anti-short from working its way out.


Thanks. This is what I will do.


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## Jim Port (Sep 21, 2007)

MC cable does not have the bond wire, nor are redheads required by code. Many continue to use them out of habit. The sheath on MC is not for grounding.


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## lmm (Jul 22, 2014)

can I use romex cable clamps with MC armored cable or do I need specific clamps?


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## gregzoll (Dec 25, 2006)

I just want to say why are you playing with live wires? Are you trying to see if the Circuit breaker is doing its job?


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## gregzoll (Dec 25, 2006)

lmm said:


> can I use romex cable clamps with MC armored cable or do I need specific clamps?


They make specific clamps that have a base, to keep from pushing the MC all the way into the box.


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## gregzoll (Dec 25, 2006)

Jim Port said:


> MC cable does not have the bond wire, nor are redheads required by code. Many continue to use them out of habit. The sheath on MC is not for grounding.


My area requires the Redheads to be used. No getting around it.


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## Jim Port (Sep 21, 2007)

gregzoll said:


> My area requires the Redheads to be used. No getting around it.


That's fine, but it is beyond the NEC requirements. Is there an adopted amendment to the NEC that the inspector can show if you do not install them?

. It it unreasonable to expect someone to know every little quirk in every Podunk. My signature clearly states the same. Your posting of that does not mean my answer was wrong. It just may not fly in your area but is perfectly acceptable in many areas.


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## lmm (Jul 22, 2014)

im using nm cable clamps. just wondering if it was ok to use nm clamps.


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## Jim Port (Sep 21, 2007)

No it is not.


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## lmm (Jul 22, 2014)

which clamps are recommended??


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## Stubbie (Jan 7, 2007)

gregzoll said:


> My area requires the Redheads to be used. No getting around it.


I'd like to talk to your inspector ... as to how they can require them ..  though they can do no harm it really isn't an upgrade to code requirements.

Anti short bushings are not required for mc cable. You do need the proper clamp ...

*Response from the NEC guys* .. _Anti-short bushings are not required for Type MC cable in accordance with the listing for the product. The termination fittings approved for use with Type MC cables are designed such that the wires will not come in contact with the cut edge of the armor; the throat of the fitting is small enough to prevent contact with the armor. Type MC termination fittings perform the same function for Type MC cable as Type AC terminations plus the anti-short bushing do for Type AC cable._


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## electures (Dec 22, 2009)

lmm said:


> can I use romex cable clamps with MC armored cable or do I need specific clamps?


 No. But which ever you choose, it has to be listed for use with MC cable. This will be indicated on the packaging.


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## Stubbie (Jan 7, 2007)

electures said:


> No. But which ever you choose, it has to be listed for use with MC cable. This will be indicated on the packaging.


Good point some clamps are listed mc/ac/bx ...


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## HouseHelper (Mar 20, 2007)

I like Arlington's Snap-it connectors.


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## jbfan (Jul 1, 2004)

HouseHelper said:


> I like Arlington's Snap-it connectors.
> 
> View attachment 87517


Those things suck when it comes to renovating.


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## 47_47 (Sep 11, 2007)

jbfan said:


> Those things suck when it comes to renovating.


I've found the easiest way to remove them is to tighten a small worm clamp onto the spring steel fingers, leaving 1/16"-1/8" exposed. Pull the connector back through the box. The hole will keep the fingers compressed. Remove the clamp and finish taking out the connector.


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## HouseHelper (Mar 20, 2007)

jbfan said:


> Those things suck when it comes to renovating.


I've found them very easy to remove from the box with just a screwdriver.


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## 47_47 (Sep 11, 2007)

Some I can get rather easily with the screw driver, but then I get some and get to the final leg of the spring steel and am like a dog chasing its tail.


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