# Random breaker tripping



## boot (Mar 1, 2013)

As predicted, got called back today. Flipped breaker back on , and began waiting for it to trip again, so we could isolate it (hopefully) 

After two more hours of head scratching, was lucky enough to be in the attic when the breaker tripped again. In a frightening manner , a poof of blown fiberglass and orange Sparks geysered out of the attic floor.

Pawed through fiberglass, found a piece of 1960s Romex coming up through top plate , blackened right where it exited the drill hole , above a room we never even did any work in. 

We cut an access hole in room below to retrieve the bad segment of wire as proof. There was a clean gash across the jacket, as if it had been sliced back when it was installed originally . Inside the gash the ground and neutral had been melting .

Go figure .


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## splatz (May 23, 2015)

boot said:


> As predicted, got called back today. Flipped breaker back on , and began waiting for it to trip again, so we could isolate it (hopefully)
> 
> After two more hours of head scratching, was lucky enough to be in the attic when the breaker tripped again. In a frightening manner , a poof of blown fiberglass and orange Sparks geysered out of the attic floor.
> 
> ...


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## boot (Mar 1, 2013)

Meant to say , hot and ground melting obviously


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## splatz (May 23, 2015)

Just curious, do you have a megger?


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## swimmer (Mar 19, 2011)

Good job (and luck) finding that


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## boot (Mar 1, 2013)

splatz said:


> Just curious, do you have a megger?


I don't. Sad to say (forgive my ignorance) didn't know about them until I started googling this issue last night, before I had it figured out. I'm a JY on my 3rd employer and no boss of mine has ever mentioned such a tool before! Must not be common among resi contractors round my neck of the woods.

Id like one now though!


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## telsa (May 22, 2015)

The QO breaker saved the building. ( Quick Off )


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## boot (Mar 1, 2013)

Got to love Square D QO ;-)


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## splatz (May 23, 2015)

boot said:


> I don't. Sad to say (forgive my ignorance) didn't know about them until I started googling this issue last night, before I had it figured out. I'm a JY on my 3rd employer and no boss of mine has ever mentioned such a tool before! Must not be common among resi contractors round my neck of the woods.
> 
> Id like one now though!


I'm actually kicking myself for not piping up on your first post. There has been some discussion on here whether we in general should be using meggers more. 

I think the reason used to be money, meggers were expensive, and just resistance (haha) to change. Now you can get an inexpensive decent megger from Supco for under $100, or you can get a Fluke 150x for a little over $500. 

This is the Supco that @macmikeman posted here a while back: 

https://www.amazon.com/Supco-M500-Insulation-Electronic-Megohmmeter/dp/B004OMAWIA 

Which leaves the only reason not to have and use one - stubborn resistance to change. 

It may or may not have made sense to use it when you did your original work, but it definitely would have made sense to use it when you had everything pulled apart, and I think it's very likely it would have found that skinned wire.


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## telsa (May 22, 2015)

A circuit that's tripping a QO c/b will certainly be exposed by a megger.

The OP got very lucky that he was in the attic when it blew... looking in the right direction, no less.

I must recommend that the OP obtain a toner and wand, too.

The hot being shorted to ground would show up right off during routine toner procedure.

( One always tests for it, as such a short will ruin toning operations.)

A short able to trip a QO would absolutely show up with the toner's electronics.


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## brian john (Mar 11, 2007)

boot said:


> Did some work at a house recently, after we left, HO reports tripping breaker. Non arc fault , Square D QO.
> 
> Upon return next day, I reset breaker. It trips about 30 seconds later. I reset it again , stays on for 5 min. Reset it a 3rd time, shuts off in 30 seconds.
> 
> ...


You reset a circuit breaker multiple times? 

THAT IS SUCH A NO NO, We are professional electricians we are suppose to trouble shoot and ascertain the issue why the CB tripped the first time.

This stuff ain't magic and is not self healing.


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## PlugsAndLights (Jan 19, 2016)

brian john said:


> You reset a circuit breaker multiple times?
> 
> THAT IS SUCH A NO NO, We are professional electricians we are suppose to trouble shoot and ascertain the issue why the CB tripped the first time.
> 
> This stuff ain't magic and is not self healing.


I had a bad experience, which could have been much worse, a few years
ago when I reset a breaker immediately after it tripped. Lesson learned. 
P&L


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## HackWork (Oct 2, 2009)

splatz said:


> I think the reason used to be money, meggers were expensive, and just resistance (haha) to change. Now you can get an inexpensive decent megger from Supco for under $100, or you can get a Fluke 150x for a little over $500.


I have a Fluke 1507 (I'm pretty sure it's an 07, it's the one without all the DMM functions) that I bought for $250 off of eBay. At the time they were selling brand new for around $430, not sure if they went up in price.

But even at $500, it's a tool that an electrician should have.



splatz said:


> It may or may not have made sense to use it when you did your original work, but it definitely would have made sense to use it when you had everything pulled apart, and I think it's very likely it would have found that skinned wire.


Agreed 100%. For a non-repeatable short like this, a megger is the right tool to use.


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## HackWork (Oct 2, 2009)

telsa said:


> A circuit that's tripping a QO c/b will certainly be exposed by a megger.
> 
> The OP got very lucky that he was in the attic when it blew... looking in the right direction, no less.
> 
> ...


I don't know about this...

The whole point here is that it *wasn't* shorting (until it did again). So the toner wouldn't show anything.

The OP used an amp probe and had zero current flowing. The short was only happening intermittently, probably when the temperature of the conductors changed enough to make them move into contact. 

A megger would find that "almost" short by jump the gap at the times when it wasn't an actual short.

No?


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## boot (Mar 1, 2013)

PlugsAndLights said:


> brian john said:
> 
> 
> > You reset a circuit breaker multiple times?
> ...


Admittedly , I reset a few times repeatedly when I was at the initial stage of thinking it was a bad breaker. After I replaced the breaker , it had seemed to hold. All of my subsequent resets were performed in between pulling suspected problem items on the circuit. Which periodically have the illusion of having found the issue (while it was holding for long durations , on one occasion the damaged wire held for 2 hours.)

I will say I've learned a lesson though , that there can be coincidences. By Day 2, I was convinced we messed something up and I had to find it. Ive been off an on at their house since last August, so I know it's legit that this breaker only just started tripping , so as they were beginning to give us the stink eye that we caused it- well, I was thinking the same as them !

Now I know to look deeper after inspecting our own work, because it's not impossible there's a new problem , starting on a part of a circuit we didn't touch ! I know you guys call it luck, but wow , after occasions like that - feels like something more to a simple fellah such as myself.

I looked at Meggers online the night I first posted , because my search terms for my issue brought them up as ideas in other forums . There was such a huge selection. Obviously Fluke is always good , but if there's quality for 100, I'm very excited for the Supco lead. Thanks for very much your input guys


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## boot (Mar 1, 2013)

Another thing ...

I wasn't entirely sure if non arc breakers would trip outside of overheating and overloads . A part of me wondered if some weird high frequency fluke or inductive load could set them off at low current. That was part of my confusion.

Henceforth, I'm going to always play it safe and assume I have a definite short to locate .


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## 99cents (Aug 20, 2012)

An easy way to test a breaker is to put it on a circuit you know is good.


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## MechanicalDVR (Dec 29, 2007)

splatz said:


> I'm actually kicking myself for not piping up on your first post. There has been some discussion on here whether we in general should be using meggers more.
> 
> I think the reason used to be money, meggers were expensive, and just resistance (haha) to change. Now you can get an inexpensive decent megger from Supco for under $100, or you can get a Fluke 150x for a little over $500.
> 
> ...


I was taught to check new circuits with a megger before ever flipping on the breaker, this practice hasn't let me down yet. 

I've used a lower priced Amprobe model for this type of thing and the more expensive Fluke for motor and compressor testing / troubleshooting.

The Supco is a great visual aid for customer explanations.


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## MechanicalDVR (Dec 29, 2007)

brian john said:


> You reset a circuit breaker multiple times?
> 
> THAT IS SUCH A NO NO, We are professional electricians we are suppose to trouble shoot and ascertain the issue why the CB tripped the first time.
> 
> This stuff ain't magic and is not self healing.


He was engaged in the "pow" testing method.


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## MechanicalDVR (Dec 29, 2007)

boot said:


> Admittedly , I reset a few times repeatedly when I was at the initial stage of thinking it was a bad breaker. After I replaced the breaker , it had seemed to hold. All of my subsequent resets were performed in between pulling suspected problem items on the circuit. Which periodically have the illusion of having found the issue (while it was holding for long durations , on one occasion the damaged wire held for 2 hours.)
> 
> I will say I've learned a lesson though , that there can be coincidences. By Day 2, I was convinced we messed something up and I had to find it. Ive been off an on at their house since last August, so I know it's legit that this breaker only just started tripping , so as they were beginning to give us the stink eye that we caused it- well, I was thinking the same as them !
> 
> ...


I feel pretty confident that the Supco would have found this one.


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## MechanicalDVR (Dec 29, 2007)

My favorite little megger for general use. They run just over $100 right now, better for a real reading than the Supco.


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## Switched (Dec 23, 2012)

MechanicalDVR said:


> My favorite little megger for general use. They run just over $100 right now, better for a real reading than the Supco.


But.... But... Where is the green and red lights!


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## MechanicalDVR (Dec 29, 2007)

Switched said:


> But.... But... Where is the green and red lights!


That's why I say the Supco is great for a selling tool to customers, this one just gives a real reading.


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## Switched (Dec 23, 2012)

MechanicalDVR said:


> That's why I say the Supco is great for a selling tool to customers, this one just gives a real reading.


Yeah, I like them too because I enjoy watching the needle move!


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## HackWork (Oct 2, 2009)

Using the Supco as a selling tool reminds me of the lie detector they gave that young kid in _The Wire_.

Only the cool people who watched The Wire will know what I am talking about.


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## splatz (May 23, 2015)

I don't know if it would be an advantage with a megger, but sometimes an actual needle on an analog meter is better because you can see very brief intermittent blips that a digital meter might miss. I know sometimes with controls work I'll break out the mighty Simpson.


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## MechanicalDVR (Dec 29, 2007)

splatz said:


> I don't know if it would be an advantage with a megger, but sometimes an actual needle on an analog meter is better because you can see very brief intermittent blips that a digital meter might miss. I know sometimes with controls work I'll break out the mighty Simpson.


I do like that feature on the little megger I use. If the moves you can figure it isn't a line to line short in a compressor as much as it could be moisture or acid in the oil. Then you can drain it and recheck and find it was the oil.


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## bartstop (Sep 30, 2012)

I had a similar situation a while back. It was a service call to an older rental house that had been remodeled many times over the years. The breaker would trip randomly. I braved the crawlspace on three separate occasions before I finally found it. I just happened to tug on a cable that went up in to a wall, it pulled right out. It had been cut and abandoned at some point in the past (handyman remodel?). They were damn lucky the place didn't go up.


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## MechanicalDVR (Dec 29, 2007)

bartstop said:


> I had a similar situation a while back. It was a service call to an older rental house that had been remodeled many times over the years. The breaker would trip randomly. I braved the crawlspace on three separate occasions before I finally found it. I just happened to tug on a cable that went up in to a wall, it pulled right out. It had been cut and abandoned at some point in the past (handyman remodel?). They were damn lucky the place didn't go up.


Wow, crazy what happens in resi during remodels!


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