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Charging station in detached garage

I'm a potential future MY owner and doing some of the research of owning an EV. My house has detached garage which has 110V for lights and garage door opener. There is no breaker box in the garage and conduit/wire has been run from the house. Investigating what's involved in getting an EV charging station in the garage. The garage is about 100 feet from the side of the house closest to the breaker box so this means running conduit/wire through the ground (mostly grass and gravel but there is some cement sidewalk). Using the existing conduit doesn't look possible as it is on the other side of the house. Interested in hearing similar experience and costs involved.
 

Sophias_dad

Active Member
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Jul 29, 2018
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Massachusetts
How much of a charge rate do you need? Could you get by with 15 or 20 amp 120V charging? Do you know what wire gauge has been laid already? If its 12 gauge you can change the breaker and outlet to 20 amps and get more charge speed. It may already be more than 12 gauge(10), because it sounds like its a long run.

You can ignore the lighting and garage door loads for the purposes of charging, if you change the bulbs to LEDs.

I'm surprised that they ran the conduit from the other side of the house. Even if it is on the other side, its most likely easier and cheaper to feed(more likely pull) wires for a new subpanel through the conduit than to put any new-laid wires in. Try to determine the diameter of the conduit, which will determine the size of the wires you'll be able to run through it(you'll need three plus a ground, unlike the two-plus-ground you probably already have).

If you DO need to lay new conduit outside, getting under a sidewalk is usually no big deal, the electrician would already have a trench leading up to and away from the sidewalk and will drive a pipe or what have you from one side to the other without having to touch the sidewalk itself. See 'bullet mole' or any number of competing products.
 
I have a similar set-up. Unfortunately the wire that runs from the house to the garage is not thick enough for 240v, so the plan is to run new wire through the existing conduit (it is large enough for the thicker wire) and put a sub-panel in the garage which will provide 240v for the car and 110v for the lights and garage door opener. I have a quote for about $2300 for all that. Fortunately we do not have to dig a new trench for a new conduit as that would add another $1000 to the cost. I am in northern NJ (expensive part of the world), so your costs may be less.

I am going to try to charge with 110v and see how that goes (getting the car in July). We will use the car less than 15 miles/day unless we are going on a trip. I should be able to keep it charged for daily driving and there are several supercharging stations nearby if needed. I have read that charging on 110 is fine as long as you don't have a long daily commute.

Here is my previous discussion on this topic: Cost to run dedicated 240v 60amp line to garage
 
Last edited:

jcanoe

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Oct 2, 2020
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Maryland
If your daily driving is minimal (less than 30 miles per day) then charging at 120V will be sufficient provided you have at least 10 hours a day when the Tesla is plugged in, charging. In winter you will find that preconditioning the Tesla to warm the battery pack and the passenger cabin will consume far more power (7kW to 8kW) than the 1.4kW power available if you are charging at 120V and 12 amps.

Until you can complete an electrical service upgrade since you will want to be charging at 120V and 12 amps not the lower 8 amp setting change the 120V 5-15 receptacle as it is probably more than 5 years old. Use a commercial grade or hospital grade receptacle as these are much higher grade than the typical receptacles sold loose in bins in hardware stores (these inexpensive receptacles are suitable for plugging in a table lamp, etc.)
 
Charging at 120V should be sufficient to cover my daily commute but weekend outings would need to go to a charging station. This is an option but longer term, I'd like to be able to charge at home.

I think the existing conduit was run on the other side of the house as that is the shortest distance between house and garage. The existing conduit also runs a wire to the sump pump located between the house and the garage. Since there's already couple wires in the conduit, don't know if you can fish another wire to the garage.

Good point about increasing the breaker AMPs for the garage, currently 15A. But I'll need to check the wire gauge to the garage. Can I just look at the copper wire thickness and compare to known wire gauge thickness?

If a new trench is needed, what wire gauge should be run? And is there special wire for outdoor/conduit? Does it make sense to run another wire in the trench (2 total) for possible future use since the additional cost of another wire would be minimal compared to the labor involved (I think).
 

jcanoe

Well-Known Member
Oct 2, 2020
5,332
5,823
Maryland
If you are going to trouble of running a new circuit to the garage cover all bases. I would recommend having an electrician install a sub panel in the garage; 100A if possible else 80A or 50A. Then you would be able to charge more than 1 electric vehicle at a time and still have power for lights, tools etc.
 
Sub-panel in the garage is a likely option. Would the existing garage wiring (i.e. lights, garage door opener) have to be rewired to the the sub-panel to be building code compliant or can I just leave the existing garage wiring as-is (connected to main panel in the house)?

Any electrical upgrade to the existing conduit looks to be a dead-end. The wiring in the conduit to the garage looks to 12 gauge but I opened the conduit junction box at the side of the house and see the 12 gauge wire from the conduit is connected to 14-gauge wiring to the main panel.
 

Sophias_dad

Active Member
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Jul 29, 2018
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Maybe a sketch from the OP would be helpful. If it were mine to do, I'd plan for a subpanel in the garage, and use the 12 gauge to pull at least 10 gauge through the existing conduit if its half-inch(I think 10AWG is limited to four conductors in half-inch). If its 3/4 inch conduit, I'd use 6 gauge for sure. Even 10 gauge would get you a 30 amp subpanel which is a bunch of miles per hour of charge. If I were running a new conduit, I'd probably go 4 gauge. This all assumes your main panel has sufficient supply to support another 30-60 amp load.

Even if the line from the main panel to the entry of the conduit is 14 gauge, I imagine it wouldn't be hard to upgrade to 12 gauge. Its also probably not really allowed to increase from 14 to 12 gauge in the middle of the run, but that's beside the point.
 
A3180362-8373-447E-BC8E-10986B378EBE.jpeg
 
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Sophias_dad

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Jul 29, 2018
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Massachusetts
Thanks for the sketch. It'd be good to find the diameter of the conduit for the sump/garage. At a half-inch, rather surprisingly you could still support two 12 gauge conductors for the sump and an entirely separate set of four 10 gauge conductors for a 30 amp subpanel. Not clear if you are allowed to have the 10awg ground for the subpanel also serve the sump, but even if not, that half inch conduit will definitely support 4x10 for the subpanel plus 3x14 for the sump.
 

Sophias_dad

Active Member
Supporting Member
Jul 29, 2018
2,180
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Massachusetts
Well, the good news is that's 3/4" conduit, and support 6 gauge to the subpanel. The bad news is that it won't support 4x6awg for the subpanel plus wiring for the sump pump. It could do 4x8awg plus sump wiring, though.

The bad news is that because there's doubtless insulation in that external wall, it'll really suck to send wiring through without opening the wall.
 

mrau

Authorized Driver
Supporting Member
Nov 12, 2018
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874
Mid-Michigan
If I recall correctly, a sub panel can be up to 50% of the main panel. So if you have 200 amp service at your main panel, you should be able to have a 100 amp sub panel in the detached garage. If you are going to trench in a new line anyway, might as well put in the largest size you main panel can handle.

Just a thought, an electrician would know best.
 
Don't see why not. You'd have to connect it to that current junction box or one very similar to it. That'll get you 8 gauge to the subpanel, which will support 32 amp L2 charging, likely way more than you need.

Running the new wire outside the house, replace existing conduit garage wire with heavier gauge, connecting at the existing junction box, and a subpanel in the garage is a viable option and should be less expensive than new trench.

I'd like to run the heaviest gauge wire possible to the garage, if the the sump wire doesn't fit in the conduit can dig a separate conduit for sump wire as it's only 15-20 feet from the junction box. My area permits converting garages to coach house to use as a secondary/rental suite so it would be good if this electrical upgrade effort doesn't go to waste and can be suitable for coach house if/when I ever decide to do this.
 

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