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charging at detached garage - dedicated circuit or sub panel?

SkyDog

Member
Aug 24, 2021
38
24
New Jersey
I'm getting ready for a Model Y - maybe it will come in January. Meanwhile I need to get my home charging ready. I'll be charging near a detached garage about 70' from the house, and I've decided on the Tesla Wall Connector because I'll be charging outside of the garage (but under a roof).

Garage has existing 120v wiring but I can't use that, it wasn't done up to code. So I need to have a new 240v circuit put in and that will need trenching from house to garage. A couple of electricians said it's best if I put in a sub panel, run the new line to that and run the Tesla Wall Connector from that. So a 50 amp line to the sub panel I guess gives me 30 or 40 amps to the Wall Connector, leaving some room to add 120v outlets or lights on another breaker. One electrician said that an EV charager should be on a dedicated circuit, so gave me a quote for running a 50 amp circuit from the house directly to the Wall Connector, and not touching the existing 120v wiring to the garage.

The dedicated circuit would cost less, but I think a sub panel would give me more flexibility for adding other circuits, although I don't really need that at this point, and I do have the existing 120v line. Are there any other pros or cons for dedicated circuit vs sub panel?

Note: I don't do a lot of daily driving. I'd like 40 amps or more for charging, but 30 should be fine if I can't do more.
 

Tam

Well-Known Member
Nov 25, 2012
9,508
8,649
Visalia, CA
...The dedicated circuit would cost less, but I think a sub panel would give me more flexibility for adding other circuits, although I don't really need that at this point, and I do have the existing 120v line. Are there any other pros or cons for dedicated circuit vs sub panel?...

I think you've answered yourself: pros=Cheaper cost and cons=inflexibility mean skipping the sub-panel because it suits your needs.
 

RTPEV

Active Member
Mar 21, 2016
1,033
1,200
Durham, NC
If you have the tax liability, you should be able to receive a tax credit for the installation of the charging station, so if that helps you justify spending additional funds on the more expensive solution, then you should take that into consideration.
 

ATPMSD

Member
Mar 12, 2021
350
360
Atlanta, GA
A few considerations:

If you run a 50 amp line the Wall Connector will charge at 40 amps, if you run a 60 amp then it will charge at the maximum rate of 48 amps

If you install a subpanel, then you should run 3-conductor wire. The Wall Connector only needs 2-conductor (hot-hot-ground), which means you will only be able to get 240V out of it. If you run 3-conductor (hot-hot-neutral-ground) you will have access to both 120V and 240V.

If you run a 60 amp line, and set the Wall Connector to 50 amps, you will have headroom for a 120V, 20 Amp circuit.

But if the 120V circuit you have is sufficient, it sounds like a dedicated 50- or 60-amp circuit is all you need.
 
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SkyDog

Member
Aug 24, 2021
38
24
New Jersey
One electrician said that an EV charger should be on a dedicated circuit, not on a sub panel. From my limited knowledge of these things, that doesn't make sense to me. A 50 amp circuit on a sub panel if functionally the same as a 50 amp circuit from the main panel, isn't it?
 
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Sophias_dad

Supporting Member
Supporting Member
Jul 29, 2018
1,545
1,620
Massachusetts
One electrician said that an EV charger should be on a dedicated circuit, not on a sub panel. From my limited knowledge of these things, that doesn't make sense to me. A 50 amp circuit on a sub panel if functionally the same as a 50 amp circuit from the main panel, isn't it?

There's no need to have it be dedicated, and even the official HPWC install guide shows a subpanel option (Page 24, "power sharing with subpanel")

There >might< be limitations on the largest breaker in a subpanel... that is, you might not be allowed to install a 50 amp subpanel and put a 50 amp breaker in it. TBH, if I were running a new subpanel, I'd start at 65A (6 gauge) and consider 85.
 

mociaf9

Active Member
Oct 18, 2018
2,885
5,967
CA
One electrician said that an EV charger should be on a dedicated circuit, not on a sub panel. From my limited knowledge of these things, that doesn't make sense to me. A 50 amp circuit on a sub panel if functionally the same as a 50 amp circuit from the main panel, isn't it?
Yes, EV chargers should be on dedicated circuits. But that dedicated circuit can come from a sub-panel that serves other loads, it doesn't mean that the supply to the charger has to come directly from the main panel. You just have to ensure that there's enough free capacity on the sub-panel to support your expected loads.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,819
8,430
Boise, ID
The dedicated circuit would cost less, but I think a sub panel would give me more flexibility for adding other circuits, although I don't really need that at this point, and I do have the existing 120v line. Are there any other pros or cons for dedicated circuit vs sub panel?
As a couple of people have pointed out, that's not an "or" question. That would still be a dedicated circuit as long as it is just the one thing on that one breaker coming out of the subpanel.

As to pros/cons of this whole scenario, whenever people are having to trench and run electricity out to a detached garage, I am always in favor of running that main line into a subpanel, just for the flexibility it gives you to modify things. Even if it starts out as 50A in and just one 50A out, you later might decide you want to split off some of it for some kind of 120V system for some other lights or an appliance like a garage beer fridge or something, and then you switch the car charging down to a 30A to make room and rearrange.
 

EVFamilyGrins

Member
May 4, 2021
23
16
CT
Agree with Rocky_H, the panel gives more flexibility which I find pays for itself in the future.

If your main panel will support it, I would have them price out cost of a 60A or 80A line/panel to the the garage and maybe 60A to HPWC.

Depending on the cost, never hurts to have more options to expand and as EV adoption increases will add resale value to property or maybe you will get a second EV in the future or a CT or travel needs will change requiring faster charging.
 

SkyDog

Member
Aug 24, 2021
38
24
New Jersey
Agree with Rocky_H, the panel gives more flexibility which I find pays for itself in the future.

If your main panel will support it, I would have them price out cost of a 60A or 80A line/panel to the the garage and maybe 60A to HPWC.

Depending on the cost, never hurts to have more options to expand and as EV adoption increases will add resale value to property or maybe you will get a second EV in the future or a CT or travel needs will change requiring faster charging.
I'm finding it difficult to even get electricians to return my calls - I think they might still be pretty busy with the aftermath of hurricane Ida around here. But I have had a few electricians out and they're saying that the most I can do is run 60A to a new sub panel, considering that I only have 100A to house currently. Then it's up to me how much I want to dedicate to the HPWC. I'm thinking of doing either 40 or 50A to the HPWC, leaving room for 1 more 15A circuit on the sub panel.

Actually, going with a 30A breaker to the HPWC would still charge at 21 mph which is more than sufficient for me, but I should probably use a 40 or 50A breaker because I don't see myself using the remaining circuit for anything more than running a few lights and maybe something to boost Wi-Fi signal in the garage.
 

SkyDog

Member
Aug 24, 2021
38
24
New Jersey
As to pros/cons of this whole scenario, whenever people are having to trench and run electricity out to a detached garage, I am always in favor of running that main line into a subpanel, just for the flexibility it gives you to modify things. Even if it starts out as 50A in and just one 50A out, you later might decide you want to split off some of it for some kind of 120V system for some other lights or an appliance like a garage beer fridge or something, and then you switch the car charging down to a 30A to make room and rearrange.
That's what I'm thinking now too. And what if I hate having an EV and go back to ICE - or if I sell the house someday to someone without an EV - then a charger wired to the main panel is not useful for anything else, but a sub panel could easily be used for something else.
 
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ATPMSD

Member
Mar 12, 2021
350
360
Atlanta, GA
I can do is run 60A to a new sub panel, considering that I only have 100A to house currently. Then it's up to me how much I want to dedicate to the HPWC

Wow, most electricians will tell you that you cannot have a 50A or 60A circuit added to a 100A panel as there really isn't any headroom!

I do suggest running a 60A circuit to a subpanel and then running circuits from the subpanel to the Wall Connector and 120V outlet. You can then manage the power to the Wall Connector by simply changing the breaker in the subpanel, and through settings iin the Wall Connector. Both of which are easy to change.
 

SkyDog

Member
Aug 24, 2021
38
24
New Jersey
Wow, most electricians will tell you that you cannot have a 50A or 60A circuit added to a 100A panel as there really isn't any headroom!
I currently don't have a big electric load in the house. The only big appliances I have are an electric stove and dryer. Assuming I only charge the EV overnight, the only other electric appliances running might the fridge, furnace and occasionally the sump pump. Someday I might need to upgrade service to the house, then I think my current main panel becomes a sub panel to the new main panel, at least that's how one electrician explained it.
 

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