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Subpanel upgrade question

bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
Hey folks, I've recently put in an order for an 8.5kW 2PW system and a site visit is scheduled 2 weeks from now. I've got a detached garage with an old subpanel where I currently charge my Model Y with a pre-existing NEMA 6-20 outlet. I'd like to replace that outlet with a NEMA 14-50 and also potentially have the Powerwalls installed inside the garage if it's possible. I'm pretty sure the outlet and/or PWs will require a subpanel upgrade as it's connected to a 40amp breaker on the main (150amp) panel located 50ft away. Attaching an image of what it looks like.

I received a quote from an electrician and they want $4,500 to dig a trench to run new conduit, install a 100amp panel, and NEMA 14-50 outlet in the garage.
I think that's kind of high and wonder why they couldn't just rip out the existing subpanel, fish in a higher gauge wire from the existing conduit upgrade the breaker on the main panel, and slap on a new panel. Conduit maybe too narrow?

I'm getting a second opinion this Saturday.

Or...are subpanel upgrades already factored into the quote? I'll definitely bring it up during Tesla's site visit I was just wanting to be proactive and not have it be one of the reasons the install is delayed.

Thanks
 

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holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,222
1,608
East Bay NorCal
Hey folks, I've recently put in an order for an 8.5kW 2PW system and a site visit is scheduled 2 weeks from now. I've got a detached garage with an old subpanel where I currently charge my Model Y with a pre-existing NEMA 6-20 outlet. I'd like to replace that outlet with a NEMA 14-50 and also potentially have the Powerwalls installed inside the garage if it's possible. I'm pretty sure the outlet and/or PWs will require a subpanel upgrade as it's connected to a 40amp breaker on the main (150amp) panel located 50ft away. Attaching an image of what it looks like.

I received a quote from an electrician and they want $4,500 to dig a trench to run new conduit, install a 100amp panel, and NEMA 14-50 outlet in the garage.
I think that's kind of high and wonder why they couldn't just rip out the existing subpanel, fish in a higher gauge wire from the existing conduit upgrade the breaker on the main panel, and slap on a new panel. Conduit maybe too narrow?

I'm getting a second opinion this Saturday.

Or...are subpanel upgrades already factored into the quote? I'll definitely bring it up during Tesla's site visit I was just wanting to be proactive and not have it be one of the reasons the install is delayed.

Thanks

My understanding is that Tesla never includes anything "free" in the quote. Anything they discover on site that needs upgrade/replace is an incremental cost on top of their original quote. This is a bit different than what you may see with other firms where the initial bid includes some slop for minor upgrades (like 4 extra disconnects).

If you could take a picture of your existing underground conduit next to a ruler or something to let us know the diameter... it'll help us know if you could reasonably fish a new line through and not pay for a new trench. I guess if you have a caliper you can measure the diameter that'll be cool too.
 

BGbreeder

Member
Jun 19, 2020
430
255
Bay Area
Your existing panel has 130A of breakers, you want to take out 60 (2x30),and put in 2x60 (120) for a total of 190 amps in a 125A panel, which would put you over the load limit for your old panel. You would need to add a second subpanel, with its own wires, or upgrade this panel to a new panel with new wires that will support the loads. Since you are going down this path, and have a first quote from an electrician, why not consider having them hard wire the Tesla charger directly, as that will increase your charging speeds?

As a side note, EV charging is a strenuous use of electrical components. My personal belief is it is a good idea to have every piece of the EV charging circuit back to your meter in good or great shape.

I think it is hard to know whether the estimate is reasonable without knowing lots of details; how long is the trench, what are the obstacles, what is the access to your panels, etc. I recently had a short trench done for $1400, and the contractor lost serious money doing it.

All the best,

BG
 

bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
My understanding is that Tesla never includes anything "free" in the quote. Anything they discover on site that needs upgrade/replace is an incremental cost on top of their original quote. This is a bit different than what you may see with other firms where the initial bid includes some slop for minor upgrades (like 4 extra disconnects).

If you could take a picture of your existing underground conduit next to a ruler or something to let us know the diameter... it'll help us know if you could reasonably fish a new line through and not pay for a new trench. I guess if you have a caliper you can measure the diameter that'll be cool too.
So I spent a few minutes digging a 1 ft trench outside the detached garage to find that it does not exist (as far as I could tell. heh). I did a peak in the attic of the garage to see the wire (in its outer sheath) going over the door, down the side of the door, and into the concrete slab of the garage as is. From there I can only assume the cable then comes up through the door jam of my back door and runs inside the soffits to the main panel inside. Btw It's a single-story house, the room near the backdoor was an addon so there are 2 attic entries, and kind of challenging to access certain areas up there.

Your existing panel has 130A of breakers, you want to take out 60 (2x30),and put in 2x60 (120) for a total of 190 amps in a 125A panel, which would put you over the load limit for your old panel. You would need to add a second subpanel, with its own wires, or upgrade this panel to a new panel with new wires that will support the loads. Since you are going down this path, and have a first quote from an electrician, why not consider having them hard wire the Tesla charger directly, as that will increase your charging speeds?

As a side note, EV charging is a strenuous use of electrical components. My personal belief is it is a good idea to have every piece of the EV charging circuit back to your meter in good or great shape.

I think it is hard to know whether the estimate is reasonable without knowing lots of details; how long is the trench, what are the obstacles, what is the access to your panels, etc. I recently had a short trench done for $1400, and the contractor lost serious money doing it.

All the best,

BG
Attached is a layout of what I am dealing with. Quote says about a 50ft trench, and it would be dug through where my septic tank is located. I'm not completely sure where or how big it is so it has to get surveyed first. The electrician did recommend the hardwire Tesla charger route as well before I asked him about installing a whole new panel, which I did under the assumption the powerwalls would require it if I had them installed in my garage. I just preferred to use my mobile charger and didn't want to have to worry about dismounting the Tesla Charger in the event I moved, but I'm not really against the idea of getting one.
 

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bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
Not sure how to edit, but in regards to the picture, the idea would be to run a new cable from the main panel, through my attic, and out the backyard to the detached garage. The more I am thinking about this the price I was quoted doesn't seem too bad, lol
 

holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,222
1,608
East Bay NorCal
Not sure how to edit, but in regards to the picture, the idea would be to run a new cable from the main panel, through my attic, and out the backyard to the detached garage. The more I am thinking about this the price I was quoted doesn't seem too bad, lol


Yeah I've seen on some of those forums full of solar-pros that they charge customers $40 to $50 per foot to trench conduit for ground-mount installations. If you can get things all peachy keen and permitted for $4,500, that seems pretty good.

I wonder if this cost can be applied to the tax credit on EV infrastructure investment...
 
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bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
Your existing panel has 130A of breakers, you want to take out 60 (2x30),and put in 2x60 (120) for a total of 190 amps in a 125A panel, which would put you over the load limit for your old panel
Another thought, the quote is for a 100amp 120/240 panel. If I were to put the charger on the new panel, would I still not have enough to support the load of 2 powerwalls? The only other things needing power in that garage are lights and 2 garage door openers.

I could probably just simply everything and just have the electrician run the hardline to a Tesla charger as he suggested, and then just have all my power walls and such mounted outside by my meter on the main structure.
 

h2ofun

Active Member
Aug 11, 2020
3,028
658
auburn, ca
Yeah I've seen on some of those forums full of solar-pros that they charge customers $40 to $50 per foot to trench conduit for ground-mount installations. If you can get things all peachy keen and permitted for $4,500, that seems pretty good.

I wonder if this cost can be applied to the tax credit on EV infrastructure investment...
Since the tax credit is 1000 max residential, which is about 3000 cost, ......
 
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BGbreeder

Member
Jun 19, 2020
430
255
Bay Area
How many Tesla's do you plan to charge simultaneously? If the answer is more than one, yes, I would upgrade the panels and the trench conduit and the wire. At some point, you will want to add something out there and be happy that you had some spare capacity...
 

wwhitney

Member
Nov 2, 2017
979
1,340
Berkeley, CA
Your existing panel has 130A of breakers, you want to take out 60 (2x30),and put in 2x60 (120) for a total of 190 amps in a 125A panel, which would put you over the load limit for your old panel.
That's not the way panel computations work. Article 220 of the NEC is a bit more complicated.

Regardless, that panel is old and is due for replacement.

Cheers, Wayne
 
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bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
How many Tesla's do you plan to charge simultaneously? If the answer is more than one, yes, I would upgrade the panels and the trench conduit and the wire. At some point, you will want to add something out there and be happy that you had some spare capacity...
One, for now atleast. But you're right, who knows what the future brings.

Thanks all.
 

miimura

Well-Known Member
Aug 21, 2013
6,557
6,365
Los Altos, CA
Putting the Powerwalls in the garage that far from the main panel is going to complicate things. If you can tolerate having them installed on the side of the house near the main panel, it will be much simpler.
 

bizybone

Member
Jul 21, 2021
16
11
Metro Atlanta, GA
Putting the Powerwalls in the garage that far from the main panel is going to complicate things. If you can tolerate having them installed on the side of the house near the main panel, it will be much simpler.
I think I'm leaning that way. Received my second quote from a different electrician with the same scope and they want $5,500. This electrician asked if I wanted a permit which I thought was a given but he mentioned that it wasn't illegal if I didn't get one and that it could potentially add an additional $3000 to the quote as he would need to upgrade my main panel too? I am going to get a 3rd quote and circle back with the 1st quote to see if that includes a permit.
 

h2ofun

Active Member
Aug 11, 2020
3,028
658
auburn, ca
I think I'm leaning that way. Received my second quote from a different electrician with the same scope and they want $5,500. This electrician asked if I wanted a permit which I thought was a given but he mentioned that it wasn't illegal if I didn't get one and that it could potentially add an additional $3000 to the quote as he would need to upgrade my main panel too? I am going to get a 3rd quote and circle back with the 1st quote to see if that includes a permit.
to do the work without a permit, IMO, is nuts
 
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holeydonut

Supporting Member
Supporting Member
Jun 27, 2020
2,222
1,608
East Bay NorCal
to do the work without a permit, IMO, is nuts


I agree... there's no way a good licensed electrician is offering to do work without a permit (and this type of project should require a permit).

The amount of effort folks put into getting fully licensed isn't worth a $5,500 job where the homeowner wants to do slight corner cutting.
 
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