I'd like to tap the feeder coming from my main breaker on the side of the house to supply power to an EV charger. I'd like to size the conductors to support 100A (I'm planning to upgrade my service to 200A or more in the future).

To connect the charger, I have:

  • 100A main breaker + meter on the side of the house
    • supplying 1 feeder to a subpanel inside for the house circuits
  • 45' of buried schedule 80 2" PVC conduit capped just below the meter leading to a detached garage
  • Another 45' through the wall cavity of the detached garage (I'd prefer concealing it in the wall if I can)
  • My AHJ has adopted a mostly unmodified version of the 2014 NEC

I'm looking for advice on how to do this in a code compliant way. This will be a short-term thing until I can have a professional move/upgrade my service and install a proper subpanel in the garage.

Any help is greatly appreciated!

  • What do you plan to replace the existing meter-main with when you upgrade to 200A service? Who is your utility for that matter? And is the garage the only outbuilding on the property? – ThreePhaseEel Sep 18 '18 at 23:42
  • Presumably I would replace the meter-main with whatever would be appropriate for 200A service (utility is PG&E). If viable, I'm hoping to also move it to the garage with an appropriately-sized feeder to the house. And you are correct, the garage is the only other structure separate from the house. – Wilco Sep 19 '18 at 0:00
  • Why do you wish to relocate the service to the garage? – ThreePhaseEel Sep 19 '18 at 1:50
  • The main reason is aesthetics (the service lines currently cross in front of the house, and over the roof of the garage. Because I already plan to feed a subpanel in the garage and replace the current meter/main, I thought that would be the best time to also move the service location since I'll be running wire in the same places. Whether or not the new location would work is TBD though. – Wilco Sep 19 '18 at 2:41
  • I take it the new 200A service will be overhead still? – ThreePhaseEel Sep 19 '18 at 3:12

You know you can't tap arbitrarily, but you can tap when the tap is the same ampacity as the trunk. Simply because the breaker protecting the trunk is able to protect the tap.

The problem is, you're hanging your hat on that, and your hat will fall down when you go to 200A service later.

So the first part here is some vision work, figuring out how you're going to protect that 100A branch on the happy day 200A arrives. I would propose some sort of combination meter pan + mini-panel with a main breaker and a couple of spaces for 2-pole breakers for branches. Just have that product in your mind's eye (i.e. Selected and priced) for now.

In the garage, I doubt the EV charger is rated for a 100A feed. that means you will need a subpanel - but any cheapie will do for a temporary. It simply needs to house a breaker of the ampacity specced by the charger.

I take it the 100' wire run will be a keeper, take super care to leave yourself excess length any way possible. Aluminium is your friend on a run like this.

You won't need to upsize the wire for distance. If you plan to run the garage circuit to full 100A actual draw on a regular basis, lay 120/125A wire.

  • Good points. My plan is when I upgrade to 200A I would fully replace that tap and connect the EV charger to the subpanel supplying the garage. In that case the conduit run would instead carry the feeder to the garage subpanel (or feeder to the house if it turns out I can move my weatherhead/meter/main to the side of the garage like I hope). – Wilco Sep 18 '18 at 23:55
  • 1
    Forgot to mention I only expect to pull 40-50A for the EV charger, but wanted the headroom for future needs (I believe a Tesla Model S can pull as much as 85A, so it seems likely that future vehicles could have even larger batteries with beefier charging rates). – Wilco Sep 19 '18 at 2:46

I would pull the 200A conductors now so that you don't have to buy another set later

What I would do in your situation is pull a set of 4/0 Al XHHW-2 conductors through the conduit with a 6AWG bare copper ground (these are sufficient for a 200A feeder to a dwelling unit), provided I was confident the service move was to take place. (If you really aren't confident about the move, you can pull 1/0 Al XHHW-2 now along with the 6AWG bare copper ground and put the 4/0 conductors in later -- the price difference is a bit under 40 cents to the foot per conductor.)

As to making the tap, for now...

I'd use a set of insulated mechanical connectors (often called "Polaris connectors" in the trade) and aluminum pigtails (short lengths of 1/0 will do) in the existing meter-main box to make the tap for now -- this is the simplest way to do that.

And what's going on in the garage

At the other end of this feeder branch (it's not a "tap" technically under NEC rules because it's sized for the full 100A current), I would install a full size subpanel in the garage -- a 30 space, 100 or 125A, main breaker subpanel will do the trick. This way, you only have to buy one subpanel for the garage instead of buying a small one now and a big one later, and you'll also be able to keep the existing breaker and wiring for the EV charger.

Last but not least -- meter-main suggestions

My personal choice for a meter-main for your proposed upgrade, given the large feeder to the detached garage and the need to use an EUSERC-compliant ring-type meter mounting system to meet PG&E requirements, would be a GE TSF420CSCU "farm panel", with the garage breaker (a TH(H)QL2100) in the upper (secondary) disconnect spot and the house panel fed from the main section's feed-through lugs. This way, the garage and house have separate "main disconnects" if you will, while providing spare space for outdoor circuits associated with the house.

  • This is awesome, thanks for the detailed response! Can I pull the same conductors used in the conduit through the wall cavity in the garage all the way to the subpanel without any protection? Or would I want to switch to SER (or something else) for the run through the walls (~40ft)? – Wilco Sep 25 '18 at 2:14
  • @Wilco -- I would just stick with the conduit the whole way thru -- SER cable would act as an obstacle to future upgrade plans. – ThreePhaseEel Sep 25 '18 at 2:16

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.