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 ?
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It only takes a minute to sign up.Sign up to join this community
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.
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.
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).
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.
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 )