Fire damage repair question


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Old 08-19-23, 09:49 AM
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Fire damage repair question

Hi,

The main breaker on a residential 200 amp service caught on fire, complete with impressive flames and a loud arc. The end results were that the breaker was burned to almost nothing and all of the wiring entering the box near the top, which was almost all of it, was damaged. To address the 20 or so wires that are now too short (nearly all armored cable), my plan is to connect a large junction box above the panel with a single piece of large-diameter conduit. The wires would be spliced in the junction box, and the lengthened wires would all then go into the load center through the single piece of conduit. Does this approach seem reasonable? Is there a better alternative or things I should be considering with my current plan? Regarding any code issues, the location is USA. Thanks for any information!
 
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Old 08-19-23, 10:06 AM
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I presume you already have a new 200 amp main breaker load center (of the same brand and type) with the appropriate number of C/B spaces to replace the damaged one?

Do you know for sure that fire/heat didn't damage the conductors and its insulation inside the armored cable to the extent it can prudently be used to splice to new conductors?

What was the cause of this fire damage?
 
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Old 08-19-23, 10:49 AM
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I have not gotten a replacement load center yet, although I plan to get one with at least as many spaces as the existing one. I want to plan the repair out before I start buying things.

Given the intensity of the fire, it was remarkably localized. It did help that I was on the stairs going down the basement when I heard the arcing so I was able to extinguish things quickly after getting the meter off. I am going to ensure that the insulation is OK on whatever portion of the wire gets used again.

I am not positive what caused the fire, but it appears that water entered from the service entrance. Water is not that good of a conductor, but perhaps some conductive material came along with it. It was raining hard when this happened, and there has been almost record amounts of rain here recently. A loose connection on the breaker would be another possibility, but I doubt it. There was almost no load, maybe a refrigerator and a few lights, and when the arcing started, the lights did not dim any noticeable amount. Then after a second or so the arc stopped and after another second or two, it resumed, but when it started again the lights were out. The main breaker has been almost completely burned or vaporized, so there is not a lot to look at for clues on the origin of the fire.
 
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Old 08-20-23, 02:25 AM
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I would highly recommend that you bring in a licensed electrician to look this over and do the replacement.
If water may have caused this issue this means that more than likely there was no drip loop prior to the panel which allowed the water to flow with gravity down into the panel.
 
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Old 08-20-23, 11:42 AM
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If water may have caused this issue this means that more than likely there was no drip loop prior to the panel which allowed the water to flow with gravity down into the panel.
You are right about the gravity flow of the water. It is something I had noticed and is definitely going to be corrected. I looked at some neighbors' houses, and it seems like that is the way it was done back in the day when the development was constructed. It is not an issue until there is a leak. I did not have any question about that part of the repair. However, I am interested in what people think of the one big junction box vs multiple smaller ones and ideas on how to keep the wires at least somewhat organized going from a big junction box to the load center.

​​​​​​​
 
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Old 08-21-23, 10:15 AM
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It's common to see multiple smaller (4x4" boxes) with single NM cables from the new junction box to the panel. It's inexpensive and easy.

A slicker solution is a cable trough (something like this) above or to the side of the panel, with a few shorter conduits connecting the trough to the panel. It's a bit more work since they often need to be punched/drilled for the conduit, but certainly code compliant. A few things to keep in mind if you go the trough or large junction box direction:

* Be aware of box fill. Both calculated and also just ensuring it doesn't become a rats nest of wires inside.
* Conduit (raceway) have a maximum number of current carrying conductors, which is why most installs like this you'll see multiple 3/4" conduits rather than one large 1.5" conduit. BUT the NEC does make an exception for raceways (conduits) less than 24". So AFAIK, you could do one large conduit, as long as you keep it short.
* You only need one ground sized to the largest ground wire. Then add a ground bar in your junction box or trough and connect all the grounds to it.
* Neutrals have to remain separate and appropriately sized
* I'd highly recommend wire markers to keep the hots and neutrals clear which one goes where. Remember GFI and AFCI breakers (and MWBC) need to ensure they go to the correct breaker.
 
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Old 08-22-23, 07:03 AM
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Conduit (raceway) have a maximum number of current carrying conductors, which is why most installs like this you'll see multiple 3/4" conduits rather than one large 1.5" conduit. BUT the NEC does make an exception for raceways (conduits) less than 24". So AFAIK, you could do one large conduit, as long as you keep it short.
I was aware that there is a maximum fill percentage of 40% when there are 3 or more wires and that goes up to 60% if the conduit is not more than 24 inches long. Is there also a limit on the absolute number of conductors in conduit?

A slicker solution is a cable trough (something like this)
Thanks for that link. It looks nice and is reasonably priced.
 
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Old 08-22-23, 07:26 PM
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Is there also a limit on the absolute number of conductors in conduit?
Yes. See the tables in Chapter 9 Annex C of the NEC code book.
 
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Old 08-22-23, 08:17 PM
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Is there also a limit on the absolute number of conductors in conduit?

Yes. See the tables in Chapter 9 Annex C of the NEC code book.
Annex C states that it is based on tables 1, 4, and 5 or 5A in the chapter, which give the fill limits, the size of the conduit, and the size of the conductors. So it is just doing the fill calculations for the common case where the conductors are all the same rather than being another limit on how the conduit can be filled.
 
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Old 08-23-23, 02:10 PM
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For wires of different sizes, construction, or insulation types you then have to go to Chapter 9 tables and do the calculations yourself. Nipples (Raceways 24" or less) are only allowed to be filled to 60% of their total cross-section area. (Chapter 9 tables note #4)
 
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Old 08-24-23, 07:38 AM
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For wires of different sizes, construction, or insulation types you then have to go to Chapter 9 tables and do the calculations yourself. Nipples (Raceways 24" or less) are only allowed to be filled to 60% of their total cross-section area. (Chapter 9 tables note #4)
OK. I understand the fill rules. I was concerned that there might be another limit on the absolute number of conductors that can be put into a piece of conduit based on one of the earlier replies.
 
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Old 08-24-23, 10:05 AM
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might be another limit on the absolute number of conductors that can be put into a piece of conduit based on one of the earlier replies.
If that was my reply - I apologize if I caused any confusion. Because the nipples will be under 24", the limits based on current-carrying conductors is not applicable. It's only conduit fill.
 
 

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