0

I am running a line to the garage to replace the existing one.

The garage has two standard lights, two LED motion detector lights, 2 quad (4 places to plug in) electrical outlets, 4 double electrical outlets (2 places to plug in). The garage is not insulated, nor heated and I run a Rigid table, Mastercraft mitre/radial arm saw, charge various batteries for yard equipment, and a quarter size beer fridge (warm months only).

I am installing a 20A breaker (two pole, I think it is rated 240V) on the main panel, running 12/3 awg (2 hots, I neutral, 1 ground) to the garage. I do not run anything requiring 220/240v, nor do I want it. I am installing a small panel in the garage with two 20A breakers in it. This panel says 70A, it is a Homeline (CHOM24L70SCP). Does this setup sound right? Safe?

  • Is there a reason you want to run a feeder that small? Also is this an attached or a detached garage, and what was used for the existing feeder? – ThreePhaseEel Aug 31 '19 at 21:03
  • existing line was off of main house panel from 15A breaker and I trip it a few times a summer. I want to avoid that and be able to reset at the garage. I don't need anything greater or more involved for what I do. Detached garage. – shane Aug 31 '19 at 21:16
  • Is the panel something you already have, or something you're looking to buy? Also, the existing line was run using a direct-buried cable, right? – ThreePhaseEel Aug 31 '19 at 21:17
  • I bought the sub panel, but it could be returned. The existing line was not buried, it ran over the ground (not my work) and I have trench 18"+ deep with appropriate PVC laid in. – shane Aug 31 '19 at 21:55
  • Even though you are quite sure you'll never put anything bigger here, I strongly recommend putting a much bigger panel here, simply so you have versatility. Having a full panel is a major frustration later, and it's only a few dollars more today to get a much larger panel. ThreePhaseEel and I would totally fit a 30 space :) but consider at least a 12 space/24 circuit. (The "circuit" number is baloney these days). The first thing that comes to my mind is "dust collector"... – Harper - Reinstate Monica Aug 31 '19 at 22:22
2

You might as well use that conduit for all it's worth

A 3/4", schedule 80 PVC conduit is capable of holding 3 6AWG stranded THWN wires and a 10AWG stranded bare copper ground, good for 60A. Considering that your 12/3 cable is likely to be a harder pull down that conduit, both because it's a cable (vs individual wires) and because UF at that size is made using solid wire, vs the stranded wire you get in THWN that size, I would use the individual wires here instead of wrestling an alligator of a cable down a conduit for no good reason whatsoever.

GO BIG OR GO HOME

There is absolutely no reason to use a panel as tiny as the one you suggest in this application. For not much more money than what your itty-bitty panel cost, you can get a 24-space, 100A, main breaker panel and an accessory ground bar kit for it, which will be large enough to be reused in your new garage for that matter. The main breaker being 100A isn't an issue here, since its simply a cheap way to get a local shutoff switch for all power to the garage.

In the main panel, you can then use a 60A breaker for the feeder, which means you have enough power to handle most things you'd want to do with even an expanded garage, and certainly plenty of power for your tools as of now. As to branch circuits, I would have one 20A circuit for lights and the minifridge, a 20A multi-wire branch circuit (using a 2-pole, 20A breaker) for the power tools (assuming you're only running one tool at a time), and a spare 20A circuit provisioned (for a window air conditioner or the likes). This leaves plenty of headroom for a dust collector, and/or a second 20A, 2-pole circuit for more power tools for that matter.

TORQUE ALL LUGS TO SPEC

Note that you should torque all loadcenter and breaker lugs to their manufacturer specification with an inch-pound torque wrench or torque screwdriver. In the US, this is now required by 110.14(D) in the 2017 NEC, and is a good idea anyway to keep your electrical system from losing you the race the way Greg Biffle's infamous lugnuts did.

  • Thank you for taking the time to provide the advice, I appreciate it very much! – shane Sep 1 '19 at 17:20
2

You can't make breakers trip preferentially...

Your stated goal is to have the breaker in the garage trip before the breaker in the house. That isn't going to work. Breakers do not work that way (unless the breaker in the house is Federal Pacific, sorry, inside joke there, those are notorious for tripping way too late, but that's not a desirable feature).

... But you have a better chance if they are much larger.

Since you have laid the PVC pipe anyway, my suggestion would be to forget the 12 AWG and run three 8 AWG individual wires and one #10 bare ground wire. Then the breaker in the house can be 50A. Obviously that will tend to trip later than your branch circuit 20A's.

However this marries you to the idea of a subpanel in the garage, including ground rods. It needs to be a main breaker panel, because it needs a master shutoff switch. I suppose you can use that hypercheap 2-space panel with a 20A 2-pole breaker forward-fed, since the handle-tied 2-pole breaker will double as both the master shutoff and the 20A branch circuit protection. I caution you, however, you will find this stifling - not least when the saw overloads and plunges the entire garage into darkness!

Since you have plans to build another garage in 5 years (we know how that goes, don't we :b) I suggest getting the panel you'd ultimately use there, now, and move the panel.

When you build the new garage and need to free up this panel, you may need power in this old garage in the interim. Simply straight-wire right through where the panel had been, leaving no breaker protection in the garage at all, then back at the house, downbreaker this old garage circuit to 20A. That is perfectly legit, you don't need a garage shutoff switch for a single multi-wire branch circuit. The only reason you want one is to have breakers trip in the garage first.

  • Thank you for taking the time to provide the advice, I appreciate it very much! – shane Sep 1 '19 at 17:20
0

Judging from what I read, you are running a 240v circuit to your garage for a sub panel in the garage, right ? I'm thinking that is your intent...

If that is indeed your intent, for something that small ( 2ea 20Amp circuits will run those items fine, btw ) then get a 4 space panel and install another 2-pole 240v breaker which will be a additional main in your garage, so that you have a safe way to shut down all the buss work down in that panel if you ever have to open it up again.

You will be taking the red / black and supplying it to the 2 pole breaker in you garage and obviously the white and ground each go to their proper busses as well.

This is called a "back fed main" which adds an additional / easy way to turn that sub panel off, if you ever need to.

In this new panel, remove any jumper connections that the Ground and Neutral bars have to each other. ..By code, any sub panel must have this provision because any ground fault that occur in the panel will be traveling back to the main panel via the ground only and not the neutral.

  • Appreciate the reply RE. I think that I have to buy a 2-pole, 20 A, 240v breaker but I will not have 240v in the garage. This breaker will be in my house main panel and feed out to the 2-slot sup panel in the garage via the 12/3 awg mentioned. – shane Aug 31 '19 at 21:08
  • Right. Not necessary but It would be a good extra margin of convenience and safety for yourself if you did... Your call though. – Retired Electrician Aug 31 '19 at 21:36
  • so, I think you are saying that the 12/3 into the main panel attaching to the 2-pole, 20 A, 240v breaker is safe? – shane Aug 31 '19 at 21:58
  • To be clear You'd have: 2 ea 2 pole 240v breakers. 1 in the main panel feeding the sub panel... Another ( extra )one in the sub panel in which those wires coming from your main panel would attach to ( your black / red wires). This way, an extra margin of safety and convenience by having a way to shut down the live bus bars in that main panel, making it safer for you to go into that panel, if you'd need to. And having that 2 pole main in your sub panel makes it a fast way to shut it all down if / when you're right there at the panel. Not mandatory, just extra safe / convenient...👍 – Retired Electrician Aug 31 '19 at 22:22
  • Thank you for taking the time to provide the advice, I appreciate it very much! – shane Sep 1 '19 at 17:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.