12/3 underground to garage multiple 14/2 wires to bare 12/3. No ground rod anywhere around 14 x54 detached garage

Question

I've been in this house, built in 1941, for two years now. I've been working on replacing very old wiring in the basement for some uncomfortable issues I've found. But these issues pale in comparison to what I found in the detached garage/workshop. I plugged my 5 ton electric log splitter into a 20 amp outlet and started it up, when the lights dimmed. Confused, I got my 50ft 20 amp extension cord and ran it to the house, where I had a 20 amp outlet. When I began to investigate why the lights dimmed. I discovered that the wire to that 20 amp outlet was 14/2. In fact all of the wire in the garage was 14/2 not a real big deal until I discovered that there was 14/2 run to another 20 amp outlet. I cut both of those wires immediately then traced the wire back to a square metal junction box. Opening the junction box I found multiple 14/2 wires wired to a 12/3 in a conduit down into the cement floor. With my circuit breaker finder I discovered The breaker was a 20 amp. Scared now, knowing that the 14/2 would burn up before that 20 amp would break. I turned off the breaker and replaced all the incandescent bulbs with LEDs. I started rewiring the outlets with yellow 12/2 but I'd like to keep the 14/2 for the lights. I have a sub-panel box from a previous project. I figured I'd put a 20 amp breaker for the outlets and a 15 amp for the lights. But my line is 12/3 attached (blk/wht) to a 20 amp, and my breaker total is 35.

So I started googling for how to deal with this. I couldn't find any help for my situation but I found a whole lot of questions that were answered by you guys.

So I joined to describe my mess and ask for help.

Can I install a sub-panel with my line being 20 amps? Do I need to install a ground rod because I want to install a sub-panel? If I can supply the sub-panel with 20 amps can I have a 15 and a 20? I'll likely never run more than one power tool at a time and my biggest tool would be the log splitter would 20 amps be enough? If I skipped the sub-panel can I continue the 12/3 line and rewire everything with 12/2? If I skipped the sub-panel would I still need the ground rod(s)

Answer 1

#14 in 20A circuit

#14 wire in the circuit will add a couple volts of voltage drop, but that isn't nearly enough to explain such dimming. Something else is wrong.

You're always allowed to use bigger wire than is required, so #12 is perfectly welcome on a 15A circuit. In fact, it's particularly called for when you have a long run. So I see it as a 15A circuit in which someone misapplied a 20A breaker (and perhaps some 20A "T" neutral receptacles). Seems easy enough; change the breaker and receps to 15A.

You can take the other perspective, that it's a 20A circuit in which #14 wire was improperly used, and change all the wire. Six of one, half-dozen of the other.

Anyway if you change all the #14, you will certainly disturb/re-do almost all the splices in the circuit. That will probably clear the actual problem causing the alarming voltage drop. Otherwise I'd check any splices you had not disturbed, particularly in the service panel, and particularly neutrals (which are always overlooked). This is a great time to get religion about torque screwdrivers.

The 12/3 was for a multi-wire branch circuit (MWBC)

You should spend some time reading up on those, if you want to pursue this option. But this is clearly what was intended by the original installer.

So you want a 20A circuit for tools, and a 15A circuit for lights. That is actually possible on existing wiring. A MWBC gives you two half-circuits, as it were.

Nothing says the half-circuits need to be the same ampacity. Code requires that the breaker handles be tied, not that they be the same ampacity. It is perfectly fine to have a MWBC that is 15A/20A.

So that's exactly what you do. You make the black wire the 20A leg, and connect it to receptacles. You make the red wire the 15A leg, and connect it to lights.

Setting up the MWBC breakers correctly

You need to get a 15A breaker correct for your panel, a 20A breaker correct for your panel, and a UL-listed handle-tie made by the same manufacturer that is correct for those breaker. Here, a real electrical supply house that is a dealer for your panel's line (or successor) will be able to set you up with the right kit. Trying to get that out of Home Depot would be a nightmare.

To make sure you did it right, check the voltage between the hots of the two tied breakers. It must be 240V! If it is, the MWBC will work properly. If the voltage difference is 0V, it is incorrectly phased.

It can be a real nuisance to correctly set up the breakers in a panel which is very full. In that case, you need a subpanel, all right - but you need it at the house to relieve space problems in your panel. You must never use cheats such as tandems or ignoring the handle-tie.

Answer 2

I discovered that the wire to that 20 amp outlet was 14/2

If that's also on a 20A circuit breaker, you have a dangerous situation and you need to correct this ASAP! In fact you should shut this circuit off at the panel and leave it off until you replace the breaker with a 15A one or change the wiring to 12 ga.

Scared now, knowing that the 14/2 would burn up before that 20 amp would break. I turned off the breaker and replaced all the incandescent bulbs with LEDs.

Well that's not in any way a solution to this situation!

I figured I'd put a 20 amp breaker for the outlets and a 15 amp for the lights. But my line is 12/3 attached (blk/wht) to a 20 amp, and my breaker total is 35.

There is no problem having a breaker total in a box that is greater than the source breaker amperage. But if you know that you'll be exceeding this capacity regularly you will get annoyed by the constant breaker tripping. Design the circuit properly so that it works for your intended application.

Can I install a sub-panel with my line being 20 amps? Do I need to install a ground rod because I want to install a sub-panel?

Yes you can install such a sub-panel but you need to ensure that the sub-panel's ground and neutral are not tied in the panel. Yes, you should install a ground rod if this is a detached structure.

If I can supply the sub-panel with 20 amps can I have a 15 and a 20? I'll likely never run more than one power tool at a time and my biggest tool would be the log splitter would 20 amps be enough?

Yes, but that's somewhat short-sighted. If you power needs grow you will have to re-do the whole thing.

If I skipped the sub-panel can I continue the 12/3 line and rewire everything with 12/2? If I skipped the sub-panel would I still need the ground rod(s)

I'm unclear how you made the leap from 12/3 to 12/2. But rewiring everything properly and to your local AHJ code standards is an acceptable solution.