Thread: Fire and Breakers

I am not an inspector but a journeyman electrician (Local 2) and carpenter (Local 1148), but I was called out to meet with another electrician and the Fire Marshal to try and determine why a fire started in a church. The Fire Marshal was certain it was electric in nature (which it probably was), but he was not sure why it happened. No foul play was suspected.

Anyway, there were four 20 amp circuits involved: three of which were dedicated to one receptacle in a kitchen. The fourth went to a 2-gang box where two receptacles were pigtailed. It was here that the fire undoubted started. Everything was burned past recognition, and you could only find the neutral or hot on the receptacles by the location of the ground screws. I might add that the electrician installed them bayonet style to the back of the receptacles.

After all of that background (sorry), my question is this: of the four circuits involved where the conductors were almost totally burned out and fused together, three of the breakers tripped, and one did not. The main did not trip. This was NOT the circuit on which the fire started, but I can't figure out why the breaker didn't trip under that kind of trauma. In the presence of the Fire Marshall, I pulled the breaker for testing. There was no obvious sign of any damage to it or the bus. The toggle worked fine, and it tested out to .13 ohms, as did the other ones that tripped. It is a Murray panel, and the breakers are also Murray.

Any comments?

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Originally Posted by Terry Fitzgerald

The Fire Marshal was certain it was electric in nature (which it probably was), but he was not sure why it happened.

Of course it was.
I find it ironic that he would say that. If he was not sure how can he say it was electrical?
"The fire was electrical in nature" is a knee jerk reaction in most cases.

It is entirely possible that the power was shut off before the breaker could trip. Do they know at what point the utility came and shut down power to the building?

I am not trying to imply that many fires are not started due to electrical problems, but it could have very well been something that was plugged in. This is the cause of most fires, although that still would get filed under "Cause of fire: Electrical"

If the installation was proper there should have been no fire, ESPECIALLY in a church. Churches follow different rules that other occupancies and a proper installation would have contained a fire from a receptacle before it got out of hand.

You say "bayonet style" connections. Do you mean backstab? If so this is a cause of many problems and I have seen receptacles burn up because if that. Again, the box should have contained a problem like that long enough to not cause a fire.

Thanks for your reply. I am not sure exactly when the power was turned off, but certainly after the fire department arrived. Yes, the correct term is "backstabbed." Not sure when I picked up on calling it "bayonet"...been calling it that for years. At any rate, it's always been a question in my mind why a breaker sometimes doesn't trip. I would just let it meander through the backrooms of my mind now except that it bothers me. Again, the circuit I'm talking about was clearly not the one that caused the fire.

Anyway, there were four 20 amp circuits involved: three of which were dedicated to one receptacle in a kitchen. The fourth went to a 2-gang box where two receptacles were pigtailed.

What exactly are the first 3 circuits tied to? 3 - 20 AMP circuits to a single receptacle? A 3 phase receptacle? What? We are talking metal conduit here, right? Are the 3 other circuits running through the box where the receptacle burned?

Details, man, details

Keep in mind that even though the insulation melted it's possible that the circuit that didn't trip never made contact with a ground or neutral. If it contacted another hot wire on the same hot leg the breaker wouldn't necessarily trip, depending on what the 2nd hot wire was touching when contact was made. And, if the circuit touched a wire on a different hot leg the possibility is the other breaker tripped first.

There's absolutely no surprise that a backstabbed receptacle failed. It's unusual if nothing was plugged in or no downstream load was present at the time of failure though as the failure mode involves heating of a bad connection under load.

Originally Posted by Bill Kriegh

What exactly are the first 3 circuits tied to? 3 - 20 AMP circuits to a single receptacle? A 3 phase receptacle? What?

I assumed him to mean 3 circuits to a single receptacle each. You being up a good question though, and a good point....details!

Sorry guys. Each of the three circuits had its own dedicated 20 amp receptacle which were backstabbed. Again, the main did not trip, and the fire started on the other circuit which had two receptacles which were backstabbed but pigtailed off the screws. All four circuits had the neutral and hot wire bonded quite efficiently. Probably should have taken pictures, but I didn't after crawling around in a hot, charred attic space tracking down circuits.

You ask a question why the circuit breakers didn't trip out.

Your back stab outlet probably had high impedance contact between the
bare wire and the metal part of the receptacle that locks onto it.

Now some one or person came along and plug a load into a receptacle.
This load would draw a lot current. A 20 ampere breaker should shut off/
trip when its load reaches around 16 ampere. The load connected may
had drawn only 12 ampere. But the bad connection would get red hot, in
my opinion. wire insulation would melt off. Hot wire could arc against ground wires. Now inside the outlet box, if some vermin, mice, etc. had
store nesting there. Now you have a fire.

Another thing I actually got to witness, was a short in a 18 gauge extension cord. The owner dog had bitting into it. My how how that
sparked. Luckly the customer had nothing combustible near. In this case
the 15 amp. breaker didn't trip, and the outlet was okay except for some
for some carbon black smoke on the face of the duplex receptacle.

Hope this help you. And now you know why Arc Fault Breakers are now
code require in homes.

Thanks for an interesting scenario about why the fire might have started although to my knowledge there was no load at the time, and the fire started on a circuit where the breaker DID trip and not the one where it did not. I agree wholeheartedly with the use of AFCI's...let's hope they develop a receptacle one of these days. However, my basic question is why a breaker doesn't trip all of the time even though everything says that it should. If you read all the posts so far, I have tested the breaker; there were no indications of anything wrong physically with either the breaker or the bus; three other breakers tripped; all the 20 amp duplex receptacles were backstabbed including the culprit receptacle which was also pigtailed; the neutral and hot wires of all four circuits were burned and bonded together in several places; and the main did not trip.

My question is not so much how the fire started but why the breaker did not trip.

Terry, maybe I just not understanding what it is your asking, SORRY!

"to my knowledge there was no Load at the Time, and the fire started on a circuit where the breaker did trip...."

Doe the statement above mean you load tested the breaker that feed a
receptacle where the fire started? And under this test the breaker did
trip?

"to my knowledge..." so your thinking, fire, breaker not tripping, and where the load, that would plug into the receptacle.

If you can't find the load plug into the receptacle, then the load is inside
the outlet box, that holds the receptacle in question.

My Def. of a load, doesn't mean that somethings has to be plug into a
receptacle. A load could be an intermittin short circuit inside the outlet box.

LOL! I wish I had just asked if anyone had any comments on why it is a breaker does not always trip when everything indicates that it should.

One detail we didn't get yet, how old is this wiring and how old are the breakers? Any corrosion in the panel? We know old breakers fail to trip, maybe the contacts become "fused". That's a pun, BTW.

Someone already said, if the hot wire loses insulation but does not make contact with ground or neutral, there is no cause for the breaker to trip.
The main breaker did not trip because the 3 branch circuit breakers did their job and tripped first, and the 4th circuit was not shorting out? But I'm just guessing and no electrician.

The big mystery is how a fire started in the receptacle that had no load plugged in. Must have been a loose or bare wire that finally made contact with the conduit or box and caused an arc. An arc fault won't trip a normal breaker, but I let the pros carry on with this.

Originally Posted by Terry Fitzgerald

LOL! I wish I had just asked if anyone had any comments on why it is a breaker does not always trip when everything indicates that it should.

Much critical information missing in the posts providing information to make some presumptions on why what caused the fire caused the fire, although Robert put forth some good postulations.

I agree with Robert (wording it differently, though) in that the receptacle could become the problem without a load plugged into it (notice that I am not calling the receptacle a load, though - just because the receptacle is drawing current due to a defect within the receptacle does not make that a load, it makes that a short or a ground fault instead). A short of a ground fault could then 'load the circuit' by the current being drawn through the circuit.

However, you are asking about why the breaker did not trip, so I will attempt toward providing potential answers to that.

1) The breaker is defective.

2) The load (current) being drawn through THAT breaker was insufficient to trip it.

3) It is possible for one problem to create another problem which removes the first problem from the circuit. An example would be the burned up receptacle causing those circuit conductors to overheat (without being to the point of tripping the breaker) and affect adjacent circuit conductors to the point that those secondary conductors fail, and in failing they in turn burn *one* of the circuit conductor in the original circuit in two, thereby 'switching off' the current in that originating circuit, allowing the breaker for the originating circuit to not trip while the other breakers did trip.

4) You did not actually "test" the breaker, you only "checked" for mechanical operation of the mechanism inside the breaker. Thus 1) could be the reason.

Before saying that I "tested" a breaker and all I did was "operate" the internal mechanism back and forth, I would install that breaker in another panel connected to a single dedicated receptacle and apply an adjustable load, while using a clamp on ammeter to measure the current in the circuit conductors, and adjust the load slowly higher until you reach the rating of the breaker without tripping, then continue increasing the load until the breaker does trip, or until you have exceeded the breaker rating by an amount sufficient to demonstrate that it does not trip at its rating - say 50% above its rating.

I have a setup which uses two hot air heat guns, one with a 1,000 watt and 1,500 watt setting and one which gives me the ability to adjust the setting in increments up to 1,800 watts - between the two I can adjust up to 27 amps, which should trip a 20 amp breaker.

Of course, though, even that is not a true "test" of the breaker, although it does "test" the breaker's ability to trip at its rating.

Thank Jerry, I wasn't hoping you post to this thread, that Terry F. wrote.

I think got the big picture now.

Thanks for your post, Jerry. Those are the comments I have been looking for. You are are right about the "testing" I did. I checked mechanical operation of the breaker using the toggle, and checked resistance using an ohm meter. Without applying power to it and doing as you suggested, I can't be 100% positive it is OK. You can be sure of one thing, though, when we put this back together I'm not going to use those breakers regardless of how they test out.

That was a good idea about how the circuit this breaker was on could have had a wire burn through before it could cause the breaker to trip, but I had thought of that and once I figured out what wire went where, I checked for continuity.

Anyway, thanks for some input. You might give your views on "backstabbing" if you have the time. I am thoroughly against it, but it's a very common practice.

Sorry for not replying to your post, John. Answered Jerry's and got busy.



("One detail we didn't get yet, how old is this wiring and how old are the breakers?")
I questioned the electrician who installed it, and he said about 6 years old.

("Any corrosion in the panel?")
Nothing. The bus is aluminum, but no sign of oxidization or scratches.

("Someone already said, if the hot wire loses insulation but does not make contact with ground or neutral, there is no cause for the breaker to trip.")
All four circuits had the neutral and hot fused together at several points. I had to separate them in order to do a continuity test to determine what circuit went where. In fact, I tested by reconnecting neutrals and hots at the point of the fire and then checking at the panel by putting the black (neutral) lead of the multimeter on the bus and the black lead first on the wire coming into the breaker which I removed from the panel and then on the bus clamp of the breaker with the toggle in the on position. Once I had continuity, I then turned the toggle to off which told me if there was a major mechanical problem. The breaker in question worked fine. I also tested the resistance of the breaker with the ohm function.

("The main breaker did not trip because the 3 branch circuit breakers did their job and tripped first, and the 4th circuit was not shorting out?")
Honestly, I don't know what else to think at this time, but I don't see why it didn't.

It just occurred to me that since the burned conductors from this circuit were fused together with the conductors of two of the other circuits that the fault might just have traveled over the other circuits and at least partially "ignored" the one that didn't trip. Theoretically, I suppose, it's possible.

Originally Posted by Robert S. Mattison

A 20 ampere breaker should shut off/
trip when its load reaches around 16 ampere. The load connected may
had drawn only 12 ampere.

Sorry Robert,

The breaker should trip at a load of 20 amps or more. The more over the 20 amp rating the quicker it should trip, ie 40 amp load would trip faster than a 21 amp load.

Originally Posted by Terry Fitzgerald

You might give your views on "backstabbing" if you have the time. I am thoroughly against it, but it's a very common practice.

The practice of "backstabbing" is, in my opinion, exactly that: The electrician is "backstabbing" everyone in the line above them and everyone in the line after them when it comes to occupying the building and using anything on the electrical system.

Stabbing people in the back is not, in my opinion, a good business practice, and backstabbing (in both senses) is not either.

If you set the above aside, I also feel it creates a fire hazard. Maybe not right away, but in years down the line. The house we bought here in Ormond Beach had ("had" as I have replaced many, the rest are on my list of things to do) backstab ONLY receptacles - NO SCREW TERMINALS!

MOST of the receptacles I've replaced have absolutely NO PRESSURE on the conductors, with many of the receptacles pulling off the conductors when I try to pull the receptacles and wires out from within the box! NOT GOOD!

Jerry I couldn't agree more.

Question: do you know anything about GFCI receptacles, some or must a
have slot where you slide the conductor, then tighten side screw down.
Are you allow wrap the conductor around the side terminal screw, instead
of using the slot.

Hi...thanks for posting. With GFCI receptacles, you put the conductor into the slot. The screw then clamps it, and it is a very good connection. Be careful when you put the stripped conductor end in that you don't accidentally clamp down on the plastic sheathing and not the copper. With a GFCI, you must bring the power in to the holes marked "LINE." A little saying they taught us in apprenticeship is, "Line in, Load out." Think of throwing a fishing line into the water and pulling out a load of fish!

Originally Posted by Robert S. Mattison

Question: do you know anything about GFCI receptacles, some or must a have slot where you slide the conductor, then tighten side screw down.
Are you allow wrap the conductor around the side terminal screw, instead of using the slot.

Originally Posted by Terry Fitzgerald

With GFCI receptacles, you put the conductor into the slot. The screw then clamps it, and it is a very good connection. Be careful when you put the stripped conductor end in that you don't accidentally clamp down on the plastic sheathing and not the copper.

Terry described it well.

If you strip the wire to the strip gage length (there is a strip gage on every receptacle) and insert the conductor ALL THE WAY, then the insulation will just be outside the terminal and not be a problem. Strip the wire a bit too little and what Terry described could happen - the clamp tightens on the insulation and the end of the conductor may, or may not, make any contact with the terminal, which may cause it not to work at all or to work intermittently.

If two or three hot wires from different breakers, on the same phase are joined..they create a combined path.. that won't trip one breaker.


I.e. 3 hot wires from 20amp breakers were fused near the panel, you could pull about 48 amps on any one of the downstream wires before it would trip all three breakers, more than enough power to melt the wires and make them red hot.

I've seen many people circumvent breakers by jumping one breaker to another...in effect doubling the trip current.... which is essentially is a firetrap, since the 14 or 12 gauge wire would have to pull 40-50 amps for a period long enough to trip breaker while it is overheating, so either the breaker eventually trips or the wire burns up, taking the house with it.