# Toubleshooting dead short on a 120-volt circuit.



## calboy (Feb 13, 2011)

Do any of you have a trick up your sleeve in making this process less time consuming and less of a cost on your customer?

I have been trained by the old school Union electricians from the early days when you test a wire you lick your fingers and bump your wire. This I will not do and I let my Knopp wiggy do this job. Well I am going to give you a way to find a dead short using a 300-watt light bulb and an amp probe. If you know this then you are showing your age, lol.

1. First you need to get a 300-watt light bulb and a commercial rubber socket with pigtails.
2. Have an clamp on amp probe

Now that you have the tools you need to located all receptacle on the circuit that is having the dead shot issue. Go the the main service panel and located the circuit breaker and remove the dead front and remove the branch circuit wire from the circuit breaker. Take one of the leads from the rubber socket that your lamp is screwed into and attach it to the branch circuit with a wire nut and the other end to the circuit breaker. Turn on the circuit breaker and the lamp filament will burn bright and hold the dead short from tripping the circuit breaker. Amp out the wire that is connected to the branch circuit wire and you should get a reading about .3 amps or around their. Now that you have got your reading, you go to the middle of the circuit and remove the outlet or what ever it is and amp it out. If you get a reading then you are behind the issue and if you do not then you are ahead of the issue. Either go back or go forward a couple of outlets until you narrow it down to the issue.

By doing this you will cut your time in half from removing all that is in the circuit and visually looking at each outlet. Once you have found the issue and corrected it, the lamp will burn at normal. You must use a 300-watt lamp only to do this.


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## jwjrw (Jan 14, 2010)

I usually just hook the tracer up. Finds shorts pretty easily usually.


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## brian john (Mar 11, 2007)

Ummmmmmmmm? I was going to post something but the new and improved me will just keep my mouth shut.


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## McClary’s Electrical (Feb 21, 2009)

brian john said:


> Ummmmmmmmm? I was going to post something but the new and improved me will just keep my mouth shut.


 

We miss you , guy:whistling2:


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## 480sparky (Sep 20, 2007)

calboy said:


> ........... Once you have found the issue and corrected it, the lamp will burn at normal. ........


It will burn at 'normal' brightness _until_ you remove the short circuit... _then_ it will burn at a voltage determined by Ohms Law since it is in series with any other loads on the circuit.




calboy said:


> ......You must use a 300-watt lamp only to do this.


ANY wattage lamp will do. I use 100w for this method myself as they are far far cheaper and can be had at any grocery store or gas station if I find myself in dire need of an A19 lamp.


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## oldtimer (Jun 10, 2010)

brian john said:


> Ummmmmmmmm? I was going to post something but the new and improved me will just keep my mouth shut.


 AWWW. Go ahead....... you will probably say what some of us are thinking.

:devil2:


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## calboy (Feb 13, 2011)

480sparky said:


> It will burn at 'normal' brightness _until_ you remove the short circuit... _then_ it will burn at a voltage determined by Ohms Law since it is in series with any other loads on the circuit.
> 
> 
> 
> ...


 Nice to know someone else out there has been shown he old school way.


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## 220/221 (Sep 25, 2007)

I've never used any test equipment other than a voltage tester to find a short.

I don't think I've ever spent more than a half hour looking. After unplugging all loads and turning off all switches, I just disconnect at a logical halfway point and try it again, then, repeat as needed.


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## 480sparky (Sep 20, 2007)

220/221 said:


> I've never used any test equipment other than a voltage tester to find a short.
> 
> I don't think I've ever spent more than a half hour looking. After unplugging all loads and turning off all switches, I just disconnect at a logical halfway point and try it again, then, repeat as needed.



So you repeatedly subject a circuit to a dead short?


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## 220/221 (Sep 25, 2007)

480sparky said:


> So you repeatedly subject a circuit to a dead short?


 
Yes, or as I call it, testing the breaker. :thumbup:



I have a feeling I've been thru this discussion before :laughing:. 

Circuit breakers like to take a little trip once in a while. It keeps them on their toes.


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## 480sparky (Sep 20, 2007)

220/221 said:


> ............
> 
> Circuit breakers like to take a little trip once in a while. It keeps them on their toes.



I'd really like to see some documentation on that, if you don't mind. :whistling2:


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## Southeast Power (Jan 18, 2009)

What about just swapping the hot and neutral in the panel. :thumbsup:


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## ohiosparky99 (Nov 12, 2009)

What about using that handy dandy wiggy and doing a continuity test?? might have to pull out some bulbs but you might save a breaker


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## 220/221 (Sep 25, 2007)

480sparky said:


> I'd really like to see some documentation on that, if you don't mind. :whistling2:


 
_



Trying to reset a tripping breaker a few times will do no harm.

02/25/2011

220/221

Click to expand...

_ 


Documented^

:thumbup:


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## 480sparky (Sep 20, 2007)

220/221 said:


> Documented^
> 
> :thumbup:



I see no documentation that breakers need tripping once in a while.


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## 220/221 (Sep 25, 2007)

480sparky said:


> I see no documentation that breakers need tripping once in a while.


 
_Breakers need tripping once in a while. How else are you going to know they are functioning? :laughing:_

_02/25/20011_

_220/221_



Also, to clarify, I'm talking about 120 breakers on simple circuits. I am NOT going to try and reset a 200A 480V breaker. Just turning on things like that after a repair makes my skin crawl.


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## 480sparky (Sep 20, 2007)

220/221 said:


> _......_Also, to clarify, I'm talking about 120 breakers on simple circuits. I am NOT going to try and reset a 200A 480V breaker. Just turning on things like that after a repair makes my skin crawl.



Why does a simple circuit need 120 breakers? :001_huh:


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## 220/221 (Sep 25, 2007)

You can't have _*too many*_ breakers.


Wait....you *can't* *have* too many breakers.


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## NolaTigaBait (Oct 19, 2008)

480sparky said:


> So you repeatedly subject a circuit to a dead short?


Haven't we been over this before?....Like, with the same people?


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## jbfan (Jan 22, 2007)

NolaTigaBait said:


> Haven't we been over this before?....Like, with the same people?


It's history! We failed to learn from it the first time, so we are doomed to repeat it!:thumbup:


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## janagyjr (Feb 7, 2011)

oh my goodness.

But yeah, why not do a simple continuity test?


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## kaboler (Dec 1, 2010)

I'd like to hear more about this.


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## backstay (Feb 3, 2011)

Large breakers in industrial plants are tested yearly on turn a rounds. I'm talking 600 , 1200 amp. They’re tripped, adjusted, and tripped again. I don't know if I would fault current trip a branch circuit breaker but I firmly believe all breakers in a panel, even the main should be shut off and turned back on at least once a year. I have gone into old(1970's) Sq D panels and the main wouldn't shut off. If they are stuck on will they trip?


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## brian john (Mar 11, 2007)

backstay said:


> Large breakers in industrial plants are tested yearly on turn a rounds. I'm talking 600 , 1200 amp. They’re tripped, adjusted, and tripped again. I don't know if I would fault current trip a branch circuit breaker but I firmly believe all breakers in a panel, even the main should be shut off and turned back on at least once a year. I have gone into old(1970's) Sq D panels and the main wouldn't shut off. If they are stuck on will they trip?


You have it partially right, we high current test circuit breakers, few places we work at do it yearly, usually they split the facility in 1/3's doing 1/3 of the CB's every year after 3 years we start over.

Molded case CB's are tested for instantaneous and long time operation on all 3-poles, meggered and ductored.


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## brian john (Mar 11, 2007)

220/221 said:


> Yes, or as I call it, testing the breaker. :thumbup:
> 
> I have a feeling I've been thru this discussion before :laughing:.
> 
> Circuit breakers like to take a little trip once in a while. It keeps them on their toes.



I do not want to go down this road again, but this procedure is not recommended. I have NEMA documentation backing this up. But I am out of the office for a week. 

Oregon Sat AM.


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## Mr Rewire (Jan 15, 2011)

The first thing is unplug everything on the affected circuit and do a continuity check if you have no continuity between hot and ground or hot and neutral then try and reset the breaker in 99% of the cases it will reset and the problem lies with something plugged in. If you have continuity then remove a receptacle at what you believe to be midpoint and check continuity. then check continuity at the panel. This should start the process of isolating the problem. continue to find midpoints until you find the effected outlet.


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## Flashlight (Jan 31, 2011)

The journeyman I worked for in the '80s used two pigtail sockets connected in series as a voltage tester, functional if crude. If the bulbs lit dimly it was a 120V circuit and if very brightly it was 208.


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## spec grade (Oct 8, 2009)

I have used the 100 watt lamp in series method for troubleshooting control circuit shorts in equiptment with a lot of controls.It saves a lot of control fuses while you figure out how to isolate the problem.Especially in older equiptment with no diagrahm and no wire numbering.


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## Mr Rewire (Jan 15, 2011)

Fusetron had a video mid 80s about available fault current and how fuses were better than breakers all I remember from it was it was cool watching the breakers explode. I guess the potential for this would be their in a fault situation that is why we don't use the breaker to test the circuit but use meters.


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