Home Electrical work
April 3, 2020 5:56 PM   Subscribe

No, you are not my electrician, and maybe I should hire one. but I think my homeowner skills are up to this. I've added plenty of outlets and switches but my most complicated wiring was a new 3-way switch setup. I want to add a new 20A circuit breaker/circuit to my main electric panel. The original panel is inside, and the outside main was added before my time when service was upgraded. Can I do this safely w/o compromising the service/load?

The outside panel has a main breaker of 125A, and 3 double-pole 30 amp breakers. The inside panel (the one with circuits like the dishwasher) has (2) single-pole 20A breakers and (4) single-pole 15A breakers. Shutting off all the inside breakers seems to shut all the electricity in the house (without using the 125A main outside), so all the 30A breakers outside seem to feed the ones on inside panel only. ( I haven't mapped out all the individual circuits.)

Can I safely add a new 20A circuit to the outside panel? I'm confident I can do the manual installation work but want guidance on the numbers.... Is there 'room' to run another circuit with the given existing circuits? (This will have a light load with a single outlet, nowhere close to 20A.)
posted by TDIpod to Home & Garden (14 answers total)
Just because you can, doesn't mean you should. People with "homeowner" skills are regularly electrocuted, disabled or killed attempting to muck around with their power. You need "electrician" skills for this job, indeed in some places it's a legal requirement.
posted by smoke at 6:12 PM on April 3, 2020 [8 favorites]

By outside, do you mean outdoors, on the outside of your house? I don't understand what you're describing at all, with the outside vs. inside. Maybe take some photos?
posted by fritley at 6:14 PM on April 3, 2020

Yea, household stuff like fixtures that is made 100% safe (at least while working on it) by killing the breaker for that circuit is not at all the same as pulling the face off a mains panel/subpanel.

I'd get an electrician for this, if all he's doing is the panel work it won't be that expensive. You sound competent enough to pull wire and have it ready for him (hint: leave lots of extra length, more than you think for his termination inside the box as a good electrician will be tidy but will tuck extra length in there such that you have it if you ever need it) if you wanted and if you tell him what you did (and take pictures as proof) he/she may even sign off on it such that you're covered if things go terribly wrong down the road, though I'm less sure of this part.

Just let the electrician do the work in the box then you can do the rest with impunity in my opinion. Screwing around in a box is no bueno.
posted by RolandOfEld at 6:23 PM on April 3, 2020 [3 favorites]

If the load is so light, why not just tie the new outlet to an existing circuit? It seems odd to have a single outlet on a breaker (barring those special dedicated circuits like A/C and refrigerators.)
posted by Larry David Syndrome at 6:27 PM on April 3, 2020

I am not your electrician, as you say, or a professional at all. I am a random internet person. If your question boils down to "can I add a 20A breaker to a panel with 3 double-pole 30A breakers and a 125A main breaker" the answer is yes, absent some other information not in your question. The 125A breaker on the outside panel will trip if the load on the aggregate circuits in the box is > 125A. Panels often have breakers in them with an aggregate capacity greater than the panel breaker; it's unlikely that the circuits will all be loaded at the same time, and even if they are the main breaker will trip for safety reasons. Given the numbers you are quoting you're not even going to be at the capacity of that box by adding a 20A circuit, especially a lightly loaded one.

The description of the outside and inside breakers in your question gives me pause though. In general if you have one panel feeding a sub-panel it will be fed off of one circuit, into the panel breaker of the subpanel. Your comment that all three 30A double-pole breakers feed the inside panel is...probably wrong, or very unusual wiring. My guess is that one of 30A double pole breakers feeds the entire inside box, which is pretty odd itself.

If you do insist on doing the work in the panel yourself, remember that even if you turn off the main panel breaker the panel is still live; hot circuits are coming into the panel north of the breaker even if it's off, and that's nothing to mess around with.
posted by true at 6:34 PM on April 3, 2020 [5 favorites]

Depending on location (for me) technically you would have to pull a permit, pay the fees, and get an inspection to add a new circuit. Whereas a licensed contractor could do it without all the rigamarole if the total cost is under a specific dollar amount (in my area homeowners who occupy the structure can modify existing circuits all day long, not add new).

I had an electrician add a pair of circuits to my garage for future expansion; discounting the material cost I would have paid anyway I think the 40min of labor was well worth me not messing around inside my panel (or my insurance weaseling out of liability).
posted by token-ring at 6:44 PM on April 3, 2020 [4 favorites]

the /r/homeimprovement subreddit would be a lot better for questions like this since there are going to be a lot more actual electicians and whatnot there.

However, I can almost guarantee that people are going to recommend getting an actual electrician for this. Screwing this up could literally kill people. Perhaps you as you are doing to work, perhaps in a week/month when you house catches fire and everyone inside burns up.

Also, never ever trust your life to answers to a question that includes "shoulds" and "seems" inside of it.
posted by sideshow at 6:49 PM on April 3, 2020 [3 favorites]

You don't want to go anywhere near a live bus bar—or one that might be live—unless you know exactly what you're doing. And if you have to ask, you don't.
posted by sjswitzer at 7:13 PM on April 3, 2020 [11 favorites]

No No No No.

I would not do this - and I've done a lot of non-professional electrical work.

Anything inside the panel/box is potentially going to kill you but also,

When there are multiple boxes, the issues of neutrals, grounds, and neutral-ground bonding can get tricky. Tricky in a way that you could wire the grounds/neutrals wrong, but your electrical system would work fine for years, but then cause a health risk to someone working on the lines in the box or going to your house, even if they take usual precautions.

Your breakers will shut down the hot wires. They do nothing to neutrals and grounds.
posted by sol at 4:55 AM on April 4, 2020 [3 favorites]

If you have to ask the question "Can I safely do this?", the answer is "No."

Run the conduit and install the outlet if you want; you can put a j-box with a cover near the panel at the end of your conduit run and have your wiring all pulled and ready to go. As others have said, it's an entirely different game inside the panel, and if you don't know with absolute certainty how to do the job safely and up to code, you really do risk killing yourself or someone else.
posted by xedrik at 8:31 AM on April 4, 2020 [2 favorites]

Adding another 20A circuit notwithstanding, you WILL NOT proceed until you understand exactly how the two service panels relate to each other. Electric work is done with zero guessing or assuming.
posted by humboldt32 at 9:21 AM on April 4, 2020 [1 favorite]

A long time ago I read advice that said the 3 things not to do as a homeowner are natural gas, 220 Volt electric and concrete work. First two are dangerous, the last you have to be a masochist to want to do. And yes, once the cover is off the box you are looking at 220 Volts.
posted by forthright at 12:00 PM on April 4, 2020 [1 favorite]

I would be very careful about this. It sounds like your outside box could possibly be what is know as a split-bus panel. In that case there is no main switch that cuts off all power to your house. You have to turn off all four switches on the main panel to remove power from the inside panel. But what that means is that the bus on the main panel is always hot unless you remove the electric meter. Working on a hot bus is very dangerous and not something to be attempted by an amateur.

Without knowing exactly what you have, you are better having a licensed electrician do this for you. I don't think we can give you a safe answer over the internet.
posted by JackFlash at 2:59 PM on April 4, 2020

I know it sounds obnoxious but....if you have to ask than no. There are plenty of sources of information about electric wiring, the last place I would look is here. (Well maybe not last.) The wording of your question, ("compromising the service load", "so all the 30A breakers outside seem to feed the ones on inside panel only,") really suggests you have a poor understanding of what is going on and maybe you don't know how much you don't know. When you added those "outlets" did you do any arithmetic on what the new branch circuit load would be and whether it met code? Did you use the correct volume boxes?
posted by Pembquist at 6:16 PM on April 4, 2020

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