Breaker won't trip...

[00zer]

Plug melted. Replaced the breaker. You can short hot to neutral directly and you get the usual buzz but this one came with pretty blue sparks. The lights flicker and the ceiling fan tries to turn but the breaker will not trip. The ground looks like 16 gauge wire (house was built in the late 60's but has copper wiring) and if you try to short to it, it just blows out the bare copper. I'm going back out with an Ideal circuit analyzer to check the available (prospective) short circuit current. If it's too low, I'm sure I can find the source of the extra resistance, but if it's too high, my understanding is that the breaker should still trip, it's just possible to get an arc across the tripped contacts if you exceed the rating of the CB. Anybody have any other ideas?

Thanks!

 

[roger]

First and foremost, you should not be deliberatly shorting this circuit.

How will you know how much damage you may have or have done to these conductors and their insulation within the walls.


Roger

 

[Tiger Electrical]

What brand breaker 00zer?

Dave

 

[00zer]

Type of breaker?

Type of breaker?

was GE but we installed a Square D (Homeline) because that's what the panel is.

 

[nakulak]

did it occur to you while you were melting the wires in the walls that you might have a bad breaker ?

 

[00zer]

No, really?

No, really?

OK, thank you everyone for pointing out the error of one of our electrician's ways. It has been exceptionally productive and helpful in every conceivable way. Unfortunately, I have to ask at this point if anyone has anything CONSTRUCTIVE to say. Is this forum for complaining or helping? Yes, the electrician tried to recreate a fault condition to test the replacement breaker. If you have a suggestion, I'd like to hear it. If you just want to display your superior wisdom and intellect, I can find another place to ask my questions, which are:

1) Am I correct in regard to high PSCC?

2) How do you recommend testing of a breaker or do you just assume it's good?

3) Does anyone know of other reasons why a breaker wouldn't trip?

Thanks in advance to anyone who has the guts to offer some advice and not simply take the easy road to criticism.

 

[don_resqcapt19]

00zer,

Yes, the electrician tried to recreate a fault condition to test the replacement breaker. If you have a suggestion, I'd like to hear it. If you just want to display your superior wisdom and intellect,

There is nothing wrong with the responses you received. Creating an intentional short is not an appropriate troubleshooting or breaker testing method.
1) there is no real way of know what the fault current was when the conductors were shorted.
2) the cost of doing a real test of that type of breaker would far exceed the cost of replacing it
3) the breaker is bad or there was not enough current flowing to cause it to trip
It is very possible to have a circuit were the available fault current at a remote receptacle is far below the instantaneous trip point of the breaker.
Don

 

[mdshunk]

Thanks in advance to anyone who has the guts to offer some advice and not simply take the easy road to criticism.

“Criticism may not be agreeable, but it is necessary. It fulfils the same function as pain in the human body. It calls attention to an unhealthy state of things.”

Winston Churchill said the above, and to that end, you got what you asked for. Stick your hand in a furnace , and before anyone can answer you as to whether the furnace is hot or not, your hand will be burned.

There is only one device that I am aware of for testing 15 and 20 amp molded case circuit breakers, and it is about 1,000 dollars. http://www.koinstruments.com/demo/demo.html For that price, the typical route is to simply replace any suspect breakers. Hard shorting the circuit as a test method is industrial strength stupid, I don't care how productive the guy is otherwise.

 

[charlie b]

No one is complaining, and the comment about intentionally causing a short circuit was about as constructive as you are likely to get. Speaking as constructively as I can, if you had used that investigative technique in my house, I would throw you out and call my lawyer.

Now speaking as a forum Moderator, I must ask you to knock off the sarcasm. Everyone who comes here does so of their own free will; nobody gets paid to help anyone else. Most of the time, the membership will offer whatever help they can. But nobody is going to help you, if you are rude. Consider this a warning: be polite, or look elsewhere for help.

To answer your three questions:

Question 1.
The term PSCC does not mean anything to me. Using ?prospective? in this manner is not a standard way of describing short circuit currents. I do not know of any electronic measurement tool that can predict the amount of short circuit current available at any point in any distribution system.

If you directly short circuit the output terminals of a breaker, and it does not trip, the breaker is bad. But you don?t test the replacement by shorting it out.

It is possible for the available short circuit current to exceed the rating of a breaker. When that short circuit takes place, it is possible for the internal contacts to melt together, preventing the breaker from opening the circuit. However, the amount of short circuit current available in residential applications should never exceed that level.

Question 2:
If you put in a new breaker, you should not need to test it. But I do not understand the scenario you are trying to describe. You mention a melted plug, a ceiling fan, and a light. What happened in the first place? What did the HO tell you, when they called for your assistance?

Question 3:
A breaker will not trip on a current that is only slightly above its setpoint. A 20 amp breaker, for example, might be able to sustain a current of 22 amps forever, without tripping. So I must fall back on why you are expecting the breaker to trip? What has failed, what has been damaged, and what do you know about the circumstances?

 

[petersonra]

I have to agree that deliberately introducing a short circuit (other than on a test rig) to test a CB is a bad idea. Not that it matters, but I have actually designed such test rigs. never got to see them in action though.

As one of the posters mentioned, breakers can typically hold a small amount of over current indefinitely. Take a look at the breaker specs and trip curve if you don't believe me.

Its not entirely outside the realm of possibility that there was some kind of load introduced into the outlet that led to the problem. It is entirely possible for there to be enough current in a failed plug to create enough heat to burn up an outlet without there being enough current to trip the breaker.

 

[nakulak]

00zer,


sorry if my comment set you off, that wasn't my intent.

I'm no expert, but if I were in your shoes I would

1) megger the ckt to determine if the wiring was ok,
2) shut off the panel and check the conductivity of the breaker to bus bars and neutral to bus

Don't know what got fried (you didn't give us additional info), but if you have any doubt that something isn't right after that, stick an arc fault in there and call it a day (at least you can "test" the arc fault)

 

[00zer]

What I lack in decorum, I make up for with an absence of tact.

Look, I don't want to stay on this subject but, if you read the thread, you can see that I was never at the house and did not have anything to do with the incident. It was a wireman that works for me. He has been warned but it's not like I'm going to fire the guy for making a mistake. Anybody who thinks back to their early days in the business can usually think of several things they were taught that just were not correct. The only person I wouldn't trust is the one who says he has nothing left to learn. Having said that, thanks to those who are now offering help. It is appreciated.

Question 1. There are several names used by different manufacturers. Ideal calls it ASCC or Available Short Circuit Current. Their circuit analyzers are capable of measuring what is supposedly the maximum amount of fault current available on the circuit. My understanding is, it should be over about 200 Amps for instantaneous trip. Anything less and it will take a longer period of time for the breaker to trip. We all know the general characteristics of breakers so everyone should know this. My main question was simply what happens when, for example, I measure 15kA on a circuit where the breaker is only rated for 10kA and that question has been answered. Thank you.

Question 2. The homeowner had a space heater plugged into a 15 amp receptacle on a 20 amp circuit with a 20 amp GE TQL Breaker. The plug stopped working and appeared damaged so she called us. When the plug was removed it was found to be badly melted. The first thing we did was replace the breaker because the original never tripped. The voltage was checked and appeared to be fine. The wireman shorted the wires to see if the new breaker would trip. (Yes, I know this is a very bad idea but it is what happened.) Apparently, the new breaker did not trip. The wireman called me and I told him to install a new receptacle and ask the homeowner to temporarily plug the heater into another circuit. Then I called the homeowner directly and rescheduled to come out tomorrow morning with more testing equipment. Obviously, my concern as to whether or not the breaker is able to function properly is greatly increased as we all know a short circuit can cause insulation/heat damage.

Question 3. Most of us I would think have seen graphs on fault current and breaker response. I am wondering if anyone has any ideas why a good breaker would not trip for reasons other than high/low fault current, i.e. if the neutral was shared with another circuit, would that bleed off any of the fault current? Things like that.

We will, of course, be repulling the branch circuit home run and any associated jumpers before this receptacle. I just want to understand the problem before I make it go away.

 

[00zer]

continued...

continued...

D-OH! It kicked me out so I thought it didn't post, sorry.

 

[Jraef]

It is very possible to have a circuit were the available fault current at a remote receptacle is far below the instantaneous trip point of the breaker.

I think this is the most salient point so far. We don't really know anything else about the circuit, the run etc., but shorting to neutral is not necessarily going to create a full bolted fault condition. You could have a lot of circuit resistance from conductor length and how many devices it went through first, you could have a loose neutral anywhere in the circuit, etc. etc. The old breaker may not have tripped for similar reasons. The fried receptacle may have just been a bad receptacle, or a bad termination, or a broken conductor, or a bad appliance etc. etc. Nothing you have said so far is conclusive proof of anything.

Basically, we are saying that the invalidity of your wireman's test method negates any conclusions you can draw from it.

But remember the Occam's Razor principle; "All things being equal the simplest explanation is probably the correct one" or the cause is much more likely to be the simplest thing, not the most complex. Trying to make this somehow related to the available fault current is a stretch IMHO. Start from what you know FOR SURE, then investigate what you don't know starting with the basics.

The answer is out there...

 

[don_resqcapt19]

The homeowner had a space heater plugged into a 15 amp receptacle on a 20 amp circuit with a 20 amp GE TQL Breaker. The plug stopped working and appeared damaged so she called us. When the plug was removed it was found to be badly melted.

That is a case where I probably would not expect the breaker to trip. The melted plug indicates a poor connection. This does two things, creates heat and limits the current flow.
Don

 

[electricalperson]

That is a case where I probably would not expect the breaker to trip. The melted plug indicates a poor connection. This does two things, creates heat and limits the current flow.
Don

your brilliant. also to the OP dont short ANYTHING out. flying molten metal isnt a good thing to see especially when it hits a customers carpet or walls or even worse your skin and eyes

 

[quogueelectric]

The first time my boss

The first time my boss

Yelled at me as I was arguing why I thought it was ok to short out a receptacle as I actually was doing it many moons ago in a Mariot hotel. I caught the wallpaper on fire.
As I quickly batted the small flame out with my hand we both broke out laughing hysterically and he walked away shaking his head.
This thread screams homeowner wired or handyman wired outlets. If the plug melted it seems to me the receptacle must have been wired loose and under a high load failed.
I would suggest checking all of the outlets on this circuit because there are probably more nightmares on this ckt waiting to be discovered. If you dont find a problem then I would suspect a nail through a wire somewhere but the melted plug screams homeowner work like a wire wrapped backwards and loosened when tightened or loose splice or badly knicked wire by someone that does not use strippers when devicing.I forgot to add it could also be a wire damaged in a wall by a long sawzall blade or some other carpentry or renovation which damaged the wire unknowinglyor knowingly tried to hide it by a flying splice with no wirenuts and a littletape. shorting the circuit could start a fire in the wall in a number of these examples.

 

[electricalperson]

more than likely it was backstabbed i see that a lot

 

[e57]

All breakers (and fuses) have what is referred to as a 'trip curve" - it is a plotted graph of amperage (in the millions) and time (in hundredths of seconds to minutes or more...) for the tested parameters for each make and model.

For instance this is a GE 15a AFCI It will hold 75A for nearly 10 seconds - thats a long time. And 120A for one second... Take note of the testing conditions at the bottom of the page... Open air breaker? in a 40C room with no prior load....


Shorting two wires together by slapping against each other will not have enough time to trip most breakers as the small contact area of the conductor has already blown open as the metal vaporized instantaneously.

Also as the conductors heat up - a lot - enough to melt the insulation right into a puddle - the resistance of the conductors goes up. Since the OP describes possibly ~10,000 amps through a #14, or #12 may have damaged every connection throughout the installed wiring of the circuit. If continued, possibly the feeder and main breakers too. Breakers IMO are not fool proof - the act of shorting can damage them even weld the contacts shut. And constant long term over-heating can deform thermal protection that is comprised of bi-metal strips to trigger the contacts to open.

As mentioned - the cost of testing a $5 breaker would cost you >10x's more. I take older hard to find large frame breakers into a shop that has specialized gear and proceedures to test them under controlled conditions with regulated currents matched to the breakers spec's, and even then they can not exceed certain times and values... As exceeding them to 'worst case scenario' would mean destroying the breaker - as they can and do explode with too much current.

 

[kbsparky]

Replace the PLUG

Replace the PLUG

NO ONE has mentioned that the heater cord/plug may be suspect in this case, and instructing the homeowner to plug it into another circuit would only cause the other outlet to burn up as well.

Such scenarios are common where folks attempt to use auxillary heaters as a primary heat source, exceeding the design considerations of the appliance.

At the least, you will probably have to install a new cord cap (PLUG) on the heater, at the most, throw it away and buy a new heater.