How trivial/nontrivial could this wiring job be?

Factual Questions
1

I am looking seriously at a fully electric Polestar 2 EV as my next vehicle. My house is older, with a 100 amp panel and a nearly full breaker box. My garage, which is detached, has 120V outlets and a couple of garage door openers (one for each garage door). As far as I can tell, everything in the garage runs off 120V, and the breaker for the garage is 20 amps.

Is it possible to get the garage wired up for 240 so I could put in an L2 charger without having to locate and re-trench to run new wiring (something I imagine is a little on the pricey side)? Or am I gonna have to pay a bunch of moneys to get the charging capability I want?

I’m picturing something along the lines of: After the wire left the house, it runs through conduit relatively freely, so perhaps they could simply disconnect the wires from the box, attach fish tape and pull it through to the garage, then fish the new wire (which I would assume would have to be more robust to handle the L2 charging current).

2

Pinging @Bob_Blaylock for an electrician’s expertise on this one.

3

I’m not an electrician, but… If the garage is on one breaker you’re pretty hosed. In theory 3 wire Romex (ground, hot, neutral) can carry 220v of significantly greater capacity than your 110 currently. But you can’t split 110 off to run your regular circuits.

You can probably make a 100A panel work with an EV if: you have a gas dryer, stove, and water heater. There are also gadgets that can monitor your draw and adjust your charging. But, it’s a stretch.

4

How “older” is older? If old enough, the wiring to the garage may well not be in conduit. Although there is now high amperage weatherproof sorta-Romex that’s designed and approved for direct-bury with no conduit.

The trenching can be done pretty easily with a dirt slitter, rather than a guy and a shovel.

Your real problem is the pitiful electrical supply to the house in the first place.

5

  I wouldn’t even think of trying to answer this without having an opportunity to inspect the situation in person.

  I will say this much:  Unless your house is unimaginably primitive, 240V should be available at the main breaker panel; and it should be possible, to run a 240V circuit from the panel to anywhere else in the house. ’ How expensive it would be, how unsightly it might be, that’s a whole other matter, but it is possible.

  In any event, I would not recommend this as a DIY project.  Make sure that a qualified electrician is involved.

6

Step 0: Just how much do you plan to drive this EV? What’s it’s consumption rating? If you live in a cold climate, does it have a heat pump or not? Do you prefer to crank the heat way up, or no? If you do a lot of highway driving, do you drive roughly the speed limit, or way over (drag is proportional to velocity squared so going fast kills efficiency)? If you drive say 40 miles or less per day in a moderate climate, you might be fine with L1 charging off your existing 20A circuit.

Step 1: Perform a load calculation, to see how much (if any) service capacity you have available. If you don’t have capacity, you’re looking at a service upgrade (generally, thou$ands) or a smart load-sharing control for the EVSE (hundred$).

Step 2: Do you have at least two full-size breaker spaces free? If so, you can add a 240V circuit without much trouble. If not, you may be able shoehorn one in via tandem/quadplex breakers (if your panel isn’t already stuffed full of them). If the panel is stuffed too full, you may need a sub-panel (hundred$ to thou$ands).

If you have service capacity and panel space, it probably won’t be horribly expensive. A single 20A 240V circuit will almost certainly fit in any existing conduit (if you do have conduit, and aren’t speculating about that) since it only needs two hot conductors and can share the existing ground wire.

7

Seems to me that the biggest issue is the 100A service.
If the L2 charger pulls 50A, and you decide to cook dinner and maybe run a load of laundry, you are going to trip the main breaker.

You need to look at upgrading your service to 200A.

8

If that’s not possible, is it instead possible to share the 20A service with an electric clothes dryer? Only one could be used at a time, of course.

9

Almost nobody needs 48A (60A circuit) home charging. A good ballpark EV consumption is 3 miles per kWh. Even L1 charging (12A at 120V) can replenish 40 miles of range in 10 hours (assuming conditions aren’t so cold or hot that the entire 1.44 kW feed isn’t used up by battery conditioning). The minimum L2 charging (12A at 240V) can restore 80 miles in 10 hours, or 50 miles (which covers the vast majority of commutes) in less than 6 hours.

Plenty of EVSEs can be configured at install time with the size of the circuit they’re connected to, so if you’re limited now but might do a service upgrade later, you don’t have to re-buy the EVSE.

10

Agree.

IANAE, but I believe a 240 V, 50 A circuit is what you want. A wire gauge of 6 AWG copper would suffice for standard runs, and 4 AWG for long runs.

11

House built in 1913, garage sometime in the 90s. So I’m lucky it’s been upgraded to breakers and not still old screw-in fuses. My first house, built in the 40s (I bought in 2000) still had those and it was a royal pain to deal with.

The issue isn’t really that there will be digging… It’s that it will probably go under my patio pavers and driveway, which are harder to deal with than just dirt.

12

It might be possible to run the line under the driveway without disturbing it but you’d need to get someone to look at it who knows better.

13

There are L2 charging stations within walking distance from my house. So I’d balance any cost with the inconvenience of having to park outside and charge the car every so often.

I don’t drive a lot, around 7k miles per year, so l1 charging will probably be fine but when it gets cold in Michigan, it will be a struggle to overcome the base wattage required to get the battery to accept a charge.

My second option is to put an L2 plug on the side of the house which will be much cheaper.

In any case, It won’t need to be 50amp, a 20amp charger would handle 99 percent of my needs and I use a charging station for the rest. I definitely don’t want to deal with the necessity of upgrading my electric service.

14

I’d be careful with this. I don’t know the Polestar requirements but Tesla pulls 48A and a lot of people cheap out the way you suggest. Using the 80% rule it needs to be a 60A circuit (not much more cost than a 50A breaker) and 4 AWG. Yes 4 gauge is more expensive but considering it is a one-time cost, what price safety (i.e. doing it right)?

We did it and are very happy with our life. Why not splurge on (again) a one-time cost?

15

Your options are highly dependent on how the current wiring is run to the garage. If underground conduit, then running an additional 20A circuit should be simple, assuming you only have a single 20A circuit currently. Even the smallest 1/2” conduit can hold 10 12AWG THWN conductors and two 20A circuits only need 5 (hot/neutral for the existing 120V circuit, hot/hot for the new 220V circuit, and a safety ground).

If you wanted to go to a 50A circuit you would be OK if you have a 1” or larger conduit (I think, assuming you are adding a pair of 6AWG conductors and an 8AWG ground. 1 1/4” conduit would definitely be OK.).

If the garage was wired with direct bury UF cable you will have to dig.

If the conduit is damaged anywhere along the run you will have to dig.

16

Both the car and the standard wall charger can be set to whatever amperage you want. It’s safer to use the wall charger since there’s no risk of forgetting the setting–it’s hard-coded via DIP switch.

I use a 30 A line split from my A/C and have the charger set to 24 A. It’s been perfectly fine for all my uses and will charge the car to “full” (80%) overnight.

17

I have a fairly new house, and 100A service. I had a friend who was an electrician wire it for me. Fortunately, an attached garage, so drill a hole between basement and garage with 50A service. To avoid actually hooking up the charger, I have a NEMA 14-50 socket, and connected a “range cord” (Stove plug cable) to the charger unit (also rated for 50A). It would also allow me to use the protable Tesla charger instead if there’s a problem with my wall charger. Total run is about 30 feet.

You will definitely have to pull new wire. The cable to the garage is pretty thick. You might get by with a 30A service. 50A circuit means 40A continuous draw is allowed. (80% rule) My Tesla Model 3 can charge 240V 40A (Or maybe it’s 48A, never going to try). The Tesla charger has a rotary switch to set max amps, up to 80A for Tesla luxury models. I’ve seen a few houses in the area with a kitchen stove in the garage, presumably ethnic families who put their “spicier” cooking out of the house. (Some more expensive houses come with a separate “spice kitchen” nowadays.)

Nominal charge rates - 40A gets me 56k/hr, 32A about 48k/hr. (Standard 120V 12A gets 5k/hr on a standard household 120V 15A circuit)I have the vehicle set to charge at 1AM when plugged in. Usually the only things that could be going at that time are the hot water heater, AC, and maybe the fridge or freezer. I make a point of not cooking or running the dryer, dishwasher, or oven after 1AM. So if you ran a 20A 120V off your existing panel it would charge 16A 120V which would be about 7 or 8km/hr (4 to 6mi) just, anything else - lights, garage door opener, etc. - you risk popping the garage breaker.

I have seen some setups discussed online where two outlets in the garage (or outside wall) could be twinned to produce 240V if they were fed from opposite sides of the panel, but if your garage panel is fed by a 20A circuit it’s probably a plain 110V feed.

After 2 years I had an episode where the main breaker flipped in the middle of the night - not sure why, I don’t think there was 100A draw on the house, I don’t even think the car was charging at the time - but I’ve set the car now to charge at 26A which adds about 38k/hr. and never had a repeat episode. Max range at 80% charge is 400km (240mi) so most of the time, the car is ready at 8AM. If I’ve really drained I can start it earlier. Or get by for the day with only 70% charge or 300km range, catch up next night, etc…

The cable is fairly thick. You want a professional to do it, and be sure everything is screwed down tight! You are talking an immense amount of power compared to anything else in the house. You could probably get away with a 240V 30A circuit (24A continuous draw) if that’s all the panel will take, if you let the car charge longer, and don’t run the dryer at the same time.

If you can’t run in a trench under the driveway, can you run in the air? Ugly, but simpler?

18

Would it be possible to have new service with a new meter to the garage? I know a few houses around here that have that. Could be cheaper than upgrading the 100A service?

Though, as others have said, 100A is not up to modern needs.

19

It’s a matter of being practical and realistic. The point is to think about what you actually need and evaluate the costs of various charging options instead of robotically saying “EV MUST GO BRRRR AT 48A”.

Lots of people are getting EVs to reduce driving costs. Most households do not have the service capacity (and often lack panel space) for a new 9.6kW or 11.5kW continuous load. A service and panel upgrade could easily add thousands of dollars to the job. If all that gets you is the ability to recharge your commute in an hour and a half instead of six hours (48A charging / 60A circuit vs. 12A/15A), who cares? Either way, it’s going to be ready to go in the morning. Plenty of people will reasonably choose to save money and not do a service upgrade.

Obviously, if the installation is going to involve significant effort to install wire (opening walls, installing new conduit, trenching, etc) absolutely go big on wire. #2 aluminum (good for 90A) isn’t much more expensive to buy or install than much smaller copper. Then you’re future-proofed if you do want more capacity later.

Things are also evolving as EVSE load management becomes more popular and affordable. With smart load management, the EVSE monitors the current through the service wires and tells the EV moment-by-moment how much it can safely draw without overloading either the branch circuit or the service. With that technology, you can safely put a 60A EVSE circuit on a 100A service (although how much power you can actually use will depend on the other loads in the house). If that adds say $500 over a “dumb” EVSE, it could make sense for a lot of people vs. a service upgrade.

I have a house that is capable of massive charging (400A service, lightly loaded) and I charge my EV on a 15A / 240V circuit because there was a spare #14 run to the garage that was trivial to use. I have 40 mile round-trip commute, and even in cold weather when I have to run resistance heat, I recharge in under 5 hours. Could’ve brought in an electrician to run a big new cable for faster charging, but there would have been no practical benefit. If we ever get a second EV (or PHEV) that will require a new run. We’ll probably have a 60A or 90A feeder run to a sub panel, and then still provision the second EVSE on a 20A circuit.

If you have a special time-of-use billing plan for a discount on EV electric supply rates in exchange for limiting charging to a certain window of time, that could be an argument for charging faster (to ensure being done in the inexpensive window of time).

Again, the point is: think about it, and evaluate the cost/benefit.

20

The danger comes not from the absolute power amount, but from the fact that EV charging loads the circuit to the legal maximum for hours at a time with no interruption. A 120V / 15A circuit fully loaded by a plug-in travel charger can burn your house down just the same if there is a problem - correctly sizing and properly torquing everything is just as important there.

This is why it’s best to hard-wire home EVSEs: Range sockets are meant for range duty (very intermittent as elements cycle on and off) and designed to plugged/unplugged once every few years. Cheap receptacles are a common failure point for EV charging. A receptacle also means you need upstream GFCI protection, which can mean a $200 breaker instead of a $10 breaker and manual resets if there’s ever a fault (EVSEs all contain their own GFCI and are allowed to auto-recluse; upstream GFCI is redundant and potentially annoying if the circuit doesn’t truly need a receptacle).