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Old 05-08-2016, 11:59 AM   #1
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Default A strong case for using metal JB's..

With glowing connections being (IMO) the greatest fire hazard, above and beyond any arcs, this is a good case for using metal boxes and AC or MC cable..
Or at least just metal JB's.
A glowing connection will melt through the loose wirenut and short on the metal box, thus kicking the breaker.
With a plastic box it will keep burning:

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Old 05-08-2016, 12:57 PM   #2
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I would concern myself with the glowing connections. Not the box they reside in.
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Old 05-08-2016, 02:08 PM   #3
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This video makes a good case to make your connections solid.
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Old 05-08-2016, 02:57 PM   #4
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Quote:
Originally Posted by MHElectric View Post
This video makes a good case to make your connections solid.

That is more to the tune of it, not the box material. Knock it off with the loose wiring connections. (toss those yellow wire nuts in the trash where they belong.....) Tan Twisters and strong fingers solve most problems but overstuffing wire nuts with conductors is asking for trouble.

I remember explaining ''bridge splices'' on one of the electrical forums several years ago and you would not believe the resistance of some of the other posters to such a simple problem as too many wires in a single splice. Just use the same size wire to split one big splice into two smaller count splices and keep the conductor counts below the not to exceed limits on the package.
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Old 05-08-2016, 04:10 PM   #5
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I have indeed seen connections burnt up like this.

In the video, I suspect that the overcurrent protection (breaker/fuse) has been upsize to permit the flow of excessive current.

But your point has been made, and I agree, non-combustible enclosures for electrical connection.....especially where twisting/spicing the copper wire and wire nuts (Marrettes) are not tight enough.
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Old 05-08-2016, 04:55 PM   #6
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I cut a bridge splice once, in a neutral, we thought all the power was off but missed two pass through at the bottom of three extension rings. I swear every light on the floor started strobing

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Old 05-08-2016, 07:31 PM   #7
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Quote:
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I have indeed seen connections burnt up like this.

In the video, I suspect that the overcurrent protection (breaker/fuse) has been upsize to permit the flow of excessive current.

But your point has been made, and I agree, non-combustible enclosures for electrical connection.....especially where twisting/spicing the copper wire and wire nuts (Marrettes) are not tight enough.
It does not require improperly sized OCP for a high resistance connection to overheat.

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If metal boxes really made a difference it would be code after all isn't the NEC all for safe installations:laughi ng:. Oh wait a better solution was AFCI
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Old 05-08-2016, 07:36 PM   #8
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Quote:
Originally Posted by Nutmegger777 View Post
With glowing connections being (IMO) the greatest fire hazard, above and beyond any arcs, this is a good case for using metal boxes and AC or MC cable..
Or at least just metal JB's.
A glowing connection will melt through the loose wirenut and short on the metal box, thus kicking the breaker.
With a plastic box it will keep burning:

Why stop there and get rid of Romex and use MC for residential?
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Old 05-08-2016, 08:08 PM   #9
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Quote:
Originally Posted by jrannis View Post
Why stop there and get rid of Romex and use MC for residential?
Chicago did (pipe)!

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Old 05-08-2016, 08:10 PM   #10
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The reality is unless you used industrial covers, all boxes metal or plastic have a plastic cover over the device.

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Old 05-08-2016, 08:30 PM   #11
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Quote:
Originally Posted by John Valdes View Post
I would concern myself with the glowing connections. Not the box they reside in.
Fair point.
Allow me to amend what i said; metal boxes and well-made connections can do more for safety than AFCI's ever will.
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Old 05-08-2016, 11:52 PM   #12
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But, in a different scenario, a plastic box wont cause a short and create a fire to begin with.
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Old 05-09-2016, 07:35 AM   #13
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Quote:
Originally Posted by 220/221 View Post
But, in a different scenario, a plastic box wont cause a short and create a fire to begin with.
In this video, the cause of the fire was not a short.
A dead short will [hopefully] trip the breaker
In this case it was a high-resistance "glowing" connection.
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Old 05-09-2016, 05:13 PM   #14
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Quote:
Originally Posted by Nutmegger777 View Post
In this video, the cause of the fire was not a short.
A dead short will [hopefully] trip the breaker
In this case it was a high-resistance "glowing" connection.
That's why I said "in another scenario".

A short to a grounded metal box wouldn't necessarily trip the breaker. It could just make enough contact to, well...., start a fire.

Metal boxes + NM = evil.
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Old 05-09-2016, 08:34 PM   #15
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Quote:
Originally Posted by 220/221 View Post
That's why I said "in another scenario".

A short to a grounded metal box wouldn't necessarily trip the breaker. It could just make enough contact to, well...., start a fire.

Metal boxes + NM = evil.
How would a near-zero resistance connection made between an ungrounded conductor and a grounded box (aka a short) not trip a properly working breaker?
A high-resistance, poorly made connection will glow and burn, while more or less safely contained within a metal JB, and once the wirenut's sheath burns off, the metal spring inside will eventually oxidize and the will glowing stop. Or, if the connection was was pressing against the wall of the JB, hopefully it will short and trip the breaker (Well, AFCI's ground fault detection would help here too).
What other scenario is there?
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Old 05-09-2016, 09:59 PM   #16
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Quote:
Originally Posted by 220/221 View Post

A short to a grounded metal box wouldn't necessarily trip the breaker. It could just make enough contact to, well...., start a fire.
That sounds like it should be true.

Also, it is true, I have seen it happen.

Ran for the breaker (40 dp ge), ran back and smothered before fire got beyond sawdust
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Old 05-09-2016, 10:55 PM   #17
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Even if you had a metal box, with a metal cover... the box itself would heat past 451F ... so the materials around it would ignite i would think.

As others have said ... make a proper connection to begin with .. problem solved.
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Old 05-09-2016, 11:29 PM   #18
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im sure some of you have seen ceramic wirenuts. that would keep the plastic from starting the fire!
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Old 05-10-2016, 12:20 AM   #19
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Duct tape is proper, right?
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Old 05-10-2016, 12:27 AM   #20
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i like neat! just doesnt always happen
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