to save myself some costs for adding a sub panel, I'm buying the cabling, sub panel, breakers, etc. NIM for an electrician to finish all the connections. I'm going to run the cables, etc. I'm wanting to add a sub-panel in my Garage (on other side of house from main breaker). Primary reason is we bought a hybrid, and the charger I got is wanting 50 amp breaker (https://www.costco.com/juicebox-pro-40-amp-electric-vehicle-charging-station-evse-with-juicenet%2c-24-ft-cable.product.100397573.html). I then would like to be able to add a shed off the garage in the future to run power tools as needed, possibly a heater, and run new outlets for holiday lights etc on the exterior.

Some Details:

My questions are:

Thanks for any help, this site has been informative, and I tried to find matching questions, but then most people don't respond when asked for more details.

Let me know if I missed anything.

Editing to add (thanks to Harper):

I've already been talking with Master Electrician and he has worked with me in the past when replacing the 200 amp because when we moved in it was an old Stab-Lok panel that I wanted to get out of the house. In addition, permits have been pulled, but I need to adjust because they were going to be for the 200 AMP replacement and a direct line to the charging station. I since had two things happen, hired a "pro" (licensed/insured) contractor to remodel the basement and he promptly said he would, then ignored running the cabling before drywall was done. I then decided if I'm going to cut the drywall back open to run the wiring, I'll just add a larger panel and connect the charging station off of that.

  • Buy your wires LAST. Jan 6, 2020 at 8:51
  • Chargers are continuous loads so if you want to use 2 at 40 amp your new 100 amp sub will be at full load. Since you plan on a second one get a bigger panel. I would go with at least a 125 amp , probably no larger as the 150 hom breakers are ~100$ Or close I had to purchase one a couple months back I was shocked at the price.
    – Ed Beal
    Jan 6, 2020 at 14:43
  • 1
    @EdBeal That's Square D for ya. Never miss an opportunity to charge half again as much as Eaton and Siemens. Jan 7, 2020 at 1:33
  • But I don’t usually use hom, I do use QO as they are 100% rated not like the cheaper brands, just saying have to have apples to apples , most of the cheap contractor brands stop at 100/125, so I complain about the hom price but your brand preference, I can’t find what this OP really needs other than square D.
    – Ed Beal
    Jan 7, 2020 at 2:58

1 Answer 1


Big enough subpanel

That's a 20-space panel. The 40 number is baloney. I'm glad you're getting a good size panel though

However, that panel has HOM's super-cheap 100A busing, which forecloses any possibility of going 125A at another time. A panel that size should have 150A+ busing, man, Homeline lives up to its name. Consider also CH, BR, or Siemens. I don't recommend QO because the breakers are too expensive.

You do not need a main breaker in the subpanel if the garage is attached to the house. "I want it so it'll trip first and save me a walk" does not work at all.

Electrician to finish

There are three things electricians do not like.

  • Finishing a job an amateur started, because the quality of work is usually a disaster and that requires the painful "you gotta pay me to redo it" conversation.
  • Using parts supplied by the customer, because noobs usually buy the wrong stuff, again ditto.
  • Being associated in any way with ninja work for which permits have not been pulled. It is embarrassing and invites the customer to sue for not mentioning the consequences of ninja work.

And frankly, much of what you want the electrician for - the careful eye - is part of the permit and inspection process.

Conduit, however...

One way to save a lot of electrician time is to pre-lay EMT metal conduit Take the time to learn to do conduit properly; so it's tip top and waiting for wires. Also have the exact conduit length pre-measured, and have a pulling rope already in the conduit. Lay it between the main panel and the new subpanel, and I would buy and mount same before calling the pro.

Use conduit at least 1 size larger than what the conduit fill calculator says you need, because that eases the pull. And have access points at least twice as often as Code requires, every 90 or at most 180 degrees.

If you lay conduit, expect to use individual wires such as XHHW. There are so few choices here that you could buy this in advance.


The cable you linked is the wrong stuff. (What'd I just say? :)

The correct wire colors for this circuit are black, black, black, because they are larger than 6 AWG and distributors don't want to stock multi-color wires in large sizes. The ground should be green or bare #6 Cu, or black #4 Al. The wires should then be marked colors with colored electrical tape.

The correct wire size is #1 AWG Al for 100A or 1/0 AWG Al for 125A. Very few people recommend copper for 100A feeder, other than people on sales commission. Besides, the lugs are aluminum, and why create a dissimilar metal problem? Anyway, aluminum is no threat; the threat is failing to set the torque correctly. That'll cause problems on Cu and Al equally.

You want XHHW x3 + gnd in conduit, or SER cable if direct-lain. That's the Al equivalent of your chosen Cu, giving 125A. 100A cable is cheaper.

I'm stuck on 125A because the #2 Cu wires you proposed are good for 125A. The cost diff is very small, but you'll need a better panel.

Buy 2' more length than you ever thought you'd need. I did that with some 1000 kcmil Cu at $10/foot (Al wouldn't fit in the conduit!) I almost bought six 15' pieces, but buying 16.66' saved our bacon.

Buying electrical

Don't buy wire online. Buy it at your local electrical supply house, and tell them you're sick of overpaying at Home Depot (which they'll believe, because they secret-shopper Home Depot all the time, mostly to snare away any competent clerks). Check 2-3 on price to avoid the one that'll stiff you.

Once someone protested "I'm in eastern Oregon, I have to mail order." Really? Where do your local electricians get supplies? Turns out there was a Platt within 10 miles.

As a general rule, it is useless and futile to use online resources to price electrical gear. The stuff is very low price, high weight and awkward sizes, which works very much against mail order. People buy locally. Online sellers know they're dealing with noobs or the desperate, and price accordingly, padding prices even more to make their shipping charges seem not unreasonable. Some are bricks-and-mortar electrical supplies who post the "I don't wanna box it up and ship it" price online.

You just have to go locally. On the most commodity things like 12/2 Romex big-box will loss-leader But on everything else, a friendly electrical supply will trounce them, often shockingly. Price 4-11/16" square boxes at electrical supply vs big-box - you'll never trust big-box again!

More power to you

A 100A panel can definitely support 2 charging stations that provision at 50A each. If you go 125A feeder you'll have headroom for a 50A and 70A Tesla charger.

  • Unless their policy has changed Platt doesn’t sell to the general public or my local store won’t, when I moved here a few years ago I went in and they had to see my license before taking my order. I told the guy that was strange I have been purchasing from them for over 20 years and never remember having to show ID but I usually have stuff delivered. He said that was there policy if you are not putting it on an account. I will double check when they open as I need to order some stuff this morning.
    – Ed Beal
    Jan 6, 2020 at 14:58
  • @EdBeal I've never dealt with Platt, but occasionally with other places for network/telephone wiring, and I've never seen such a policy. However, I wouldn't be surprised if a particular store has had too many returns from homeowners getting the absolutely wrong stuff that they put a policy in place to weed them out. Jan 6, 2020 at 15:25
  • 2
    I just talked to platt it’s used to be company policy to only sell to people with accounts or licenses, today there are a few stores that still have that policy I just happen to have one , I called the second location in my area and they do sell to the public. I got this info from the 2nd store the first that I normally order from just said not unless I had an account so it may be a combination of old policy and or returns.
    – Ed Beal
    Jan 6, 2020 at 15:45
  • Note that you want quadplex USE/RHH/RHW-2 for direct burial work (SER can't be buried at all, see 338.12(A) point 2) Jan 7, 2020 at 1:30
  • @ThreePhaseEel I get very confused by USE/RHH etc. because all of it I find online is single-conductor. I can believe you can direct bUry that, but I don't see how you'd run it unprotected across rafters and joists where you'd use SER. Jan 7, 2020 at 1:40

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