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A sub panel caught on fire just in the garage area.

Do I need to rewire the whole house or can I just get a big junction box and splice all branch circuits and run it to my new electrical panel ?

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    Not enough information to answer that. You need a licensed and certified electrician for sure. – Alaska Man Apr 25 at 2:20
  • Do you have photos of the damage? – ThreePhaseEel Apr 25 at 2:23
  • @AlaskaMan Or better words. I think OP is assuming we know what OP is looking at, because surely everyone who has that thing happen has exactly the same thing happen. But having had someone gut the interior of my panel right up to the wire exits, I think I get it. – Harper - Reinstate Monica Apr 25 at 3:00
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Allow enough space.

A cable is 2-5 wires inside a plastic sheath.

A #14 wire needs 2.0 cubic inches.
A #12 wire needs 2.25 cubic inches.
A #10 wire needs 2.5 cubic inches.
A #8 wire needs 3.0 cubic inches.
A #6 wire needs 5.0 cubic inches.
Beyond that, it gets complicated.

All grounds together count as 1 wire of the largest size. So if you have a bunch of #14-#10 grounds, you get them all for 2.5 cubic inches total.

Suppose you're extending a 12/2 cable. That's two #12 wires from one cable, two #12 wires from the other cable (four so far). That makes 2.25 x 4 = 9 cubic inches.

Now you know how big a box (or boxes) you need.

Get a taller panel

It's always a blessing to have more spaces anyway, so go for it. You are allowed to splice with wire-nuts inside a panel.

I prefer to have multiple junction boxes, connected with EMT metal conduit.

If your panel is surface mount, this can work great. You run a 3/4" EMT conduit pipe some distance from the panel. You fit either a 4" square deep box (31 cubic inches with a domed cover (10 cubic inches), or a 4-11/16" square box (42 cubic inches). EMT metal conduit, properly fitted, is the ground path. So you simply attach a pigtaled ground screw to the screw hole in the box, and tack up your grounds and push em back into the box.

Then, down the conduit, you extend the wires using THHN individual wires. You can use all #12 wire, that'll be fine for extending #14 circuits, but mark the #12 with a flag saying "#14" or 15A, so somebody doesn't think it's good for 20A.

Either the 42 ci box or the 31+10 box+cover give enough room for 4 circuits to be extended. And that's fine because 4 circuits is the thermal maximum for EMT conduit that is longer than 2 feet.

Hot-neutral grouping matters. Wiring is NOT just "every neutral goes to the bar" - it matters which hot(s) it's with, for diagnostic and GFCI/AFCI reasons. Bundle the THHN hot-neutral groups. Wrap the pair with tape somewhere it won't be too intrusive. I recommend multi-color tape. You can even have pairs of colors, out of 6 colors of tape you can get 21 combinations. (blue-red and red-blue can't both be used, too confusing).

Don't catch your panel on fire again.

Do not use Zinsco or Federal Pacific panels, or continue them in use.

Do not use Brand X panel and put Brand Y breakers in them. That's not mindless consumerism, the bus stabs actually are different shapes and won't mesh properly cross-brand, and that starts arcing fires. If you just can't follow this rule, use Eaton CH or Square D QO. That will put you straight :)

Do not exceed stab limits. So putting the 50A/30A range-water heater quadplex across from the 100A subpanel breaker, is nope.

If a bus stab is roached, stop using it. Paint a breaker red and stick it there and use it for nothing.

Cover all unused knockouts to prevent animal entry.

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Never reuse a panel that has had a fire , the insulators may have been damaged and smoke , soot can leave conductive traces causing problems.

Sub panels are easy because you can turn them off in almost all cases. If it is legal for a home owner to do there own work this can be a DIY but a permit should be taken out and have inspections to make sure the work is up to code.

Get a torque wrench and torque each wire to the required torque

Big junction boxes are expensive, most electricians I know use gutters.

How much rewireing depends on the fire and the extent depends on damage. wires that are damaged and not able to be spliced are usually spliced in a gutter next to or under the panel.
What is a gutter it is a metal channel / box with a cover code allows 20% fill and there can be 30 current carrying conductors with no derating that’s 15 120v circuits on each side and bottom if 3 gutters are used that is more circuits than many homes have (90 ccc) I sometimes use gutters when There has been damage and sometimes for old panels. if your panel is older you may find out they are smaller than today’s panels but I usually splice the wires in the new panel if I can.

If most of your branch circuits come from the bottom you are in luck you can lower the panel (no minimum height but be realistic).

if most of your circuits enter from the top the highest breaker position needs to be below 6’7” , I have seen panels put in with the main on the bottom to gain enough room but the off position of the breakers including the main must be down or horizontal.

Make sure your breakers are properly sized for the conductors it is ok to use larger wire but on a panel repair I prefer using the size I am splicing into but if I do use larger I tag it as example (15 amp max 14 awg branch wires )

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The circuits will need testing before you can know that.

Are you sure you are going to be able to rewire it all safely because you are supposed to test it all once you have replaced the electrical panel?

It sounds a bit sketchy.

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  • Can you describe what sort of "testing" the branch circuits will need? Are you talking about a megohmmeter/insulation resistance check, which is the only thing I can think of, although not necessary if the fire damage was localized to the vicinity of the panel, which is quite possible? – ThreePhaseEel Apr 25 at 16:34
  • Yes, that's right to make sure there is no damage from any overload caused by the fire damage to the cables. Also if the subpanel set on fire then whatever caused it to go up could also cause damage to the circuit from overload. – lewwy Apr 25 at 17:45
  • All overloads caused by the fire are in the panel as 3 phase has mentioned the heat causes a short but that short is only from that to the breaker. The feeder is the only one to worry about and it’s breaker would be protecting it. – Ed Beal Apr 26 at 15:53

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