Question for home charging install - wire size

[Rocky_H]

What is the largest wire thickness the Tesla wall connector will take? Is that 4 gauge? For the cleanest install, I might just request to only use 4 gauge so you don't have to split it with a subpanel, even if that makes it be less than a 100A circuit.

Other than that, if it's going to be a 100A, the wire is just going to be too thick to use directly, and you'll have to do the subpanel anyway.

 

[brkaus]

What is the largest wire thickness the Tesla wall connector will take? Is that 4 gauge? For the cleanest install, I might just request to only use 4 gauge so you don't have to split it with a subpanel, even if that makes it be less than a 100A circuit.

Other than that, if it's going to be a 100A, the wire is just going to be too thick to use directly, and you'll have to do the subpanel anyway.

A properly sized Polaris connector will be able to add pigtails in the wall box w/o needing a sub-panel.

But I guess if that is done, the breaker would need to be downsided in the main panel and would need to be sure there is a 60a breaker that can fit the larger wires. Looks like SquareD 60A can use AWG 8 to AWG 2 aluminium/copper

All speculation w/o knowing what OP is getting.

 

[GregD60]

If it’s really 100a, I’d do something like post #7 above, but with a small sub-panel.

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Amy electrician should be able to easily come in a flush mount a box where the wire terminates.

I’d gladly pay extra for 320a service! Even if I had to have someone in to finish it. My house is so underpowered.

This is the way to go! Just have another electrician come in after the house is done to install it, run a short wire to where you want to mount the Wall Charger. As long as the wall charger will be in the same or an adjacent stud space, this should be pretty easy for any decent electrician do after the fact and have it look like original, i.e., no conduit on the walls and everything flush. When the hole is cut out for the sub panel, there should be more than enough working space to run the necessary wires through the wall. This option gives you a lot of flexibility for the future at a minimal additional cost.

If you were to get a Ford Lightning today, they have the ability to charge up to 90 amps, which requires a 100 amp circuit. With your prewiring, you'd be all set for this. Also, assuming that the Cybertruck 500 mile range version becomes a reality, I think there's a good chance that it would support a similar charging rate. Tesla could make a new Cyber Wall Charger.

 

[acarney]

Ok, I'm changing my thinking a little. Maybe a flush mount sub panel wouldn't be a deal breaker for me. I really just didn't want anything slapped on the walls like exterior conduit or a box mounted on the wall.

If they did use something like the Square D QO 100 amp flush mount panel. Would that be wired such that a 100A branch circuit was connected to it, likely using 2 AWG. Then could I see if they would run a somewhat short run (like 1.5 feet or something) of #4 Romex in the wall and down from the panel (so same cavity space between studs). Then just ask for like a 1 gang box with a blanked face plate. Mount my wall connector over that 1 gang box so it is right below the panel. Then down the road if I wanted, I could have Romex run from the sub panel up the wall cavity across the attic space of the garage and down the other wall of the garage for another EVSE if I become a 2 EV household. All that would need to be done is make sure the breakers are swapped out in the sub panel for two 40A ones which could feed two EVSE's at 32A?

If they wouldn't run anything else but just the flush mount panel. Could a competent electrician be able to connect to the panel and run a foot or two of #4 Romex in the wall directly down below the panel while only making a small cut in the drywall, like the size that would be covered/hidden by the Tesla wall connector EVSE? I don't mind if it's a crappy patch job or anything as long as my equipment could cover it.

 

[rstx]

What is the largest wire thickness the Tesla wall connector will take? Is that 4 gauge? For the cleanest install, I might just request to only use 4 gauge so you don't have to split it with a subpanel, even if that makes it be less than a 100A circuit.

Other than that, if it's going to be a 100A, the wire is just going to be too thick to use directly, and you'll have to do the subpanel anyway.

4 gauge max yes.

 

[GregD60]

Ok, I'm changing my thinking a little. Maybe a flush mount sub panel wouldn't be a deal breaker for me. I really just didn't want anything slapped on the walls like exterior conduit or a box mounted on the wall.

If they did use something like the Square D QO 100 amp flush mount panel. Would that be wired such that a 100A branch circuit was connected to it, likely using 2 AWG. Then could I see if they would run a somewhat short run (like 1.5 feet or something) of #4 Romex in the wall and down from the panel (so same cavity space between studs). Then just ask for like a 1 gang box with a blanked face plate. Mount my wall connector over that 1 gang box so it is right below the panel. Then down the road if I wanted, I could have Romex run from the sub panel up the wall cavity across the attic space of the garage and down the other wall of the garage for another EVSE if I become a 2 EV household. All that would need to be done is make sure the breakers are swapped out in the sub panel for two 40A ones which could feed two EVSE's at 32A?

If they wouldn't run anything else but just the flush mount panel. Could a competent electrician be able to connect to the panel and run a foot or two of #4 Romex in the wall directly down below the panel while only making a small cut in the drywall, like the size that would be covered/hidden by the Tesla wall connector EVSE? I don't mind if it's a crappy patch job or anything as long as my equipment could cover it.

You may as well have two 50A circuits which would each be able to charge at 40A. I believe that if you have 2 Tesla Wall Chargers, you can use power sharing between them. If you do that, I think you just use one higher amperage circuit, like 90A, but I'm not sure how everything is connected in that case.

I would just have them use their standard termination, which is probably some kind of a box. It might even be a subpanel. If it isn't a subpanel, let your own electrician install it. A hole that would be covered by the Tesla Wall Charger would be more than large enough to run the wiring for the tiny run you're looking at. It's really not very hard to run wires inside the wall for short runs where you don't have to cross multiple studs. You shouldn't need any kind of patch job.

 

[brkaus]

Ok, I'm changing my thinking a little. Maybe a flush mount sub panel wouldn't be a deal breaker for me. I really just didn't want anything slapped on the walls like exterior conduit or a box mounted on the wall.

If they did use something like the Square D QO 100 amp flush mount panel. Would that be wired such that a 100A branch circuit was connected to it, likely using 2 AWG. Then could I see if they would run a somewhat short run (like 1.5 feet or something) of #4 Romex in the wall and down from the panel (so same cavity space between studs). Then just ask for like a 1 gang box with a blanked face plate. Mount my wall connector over that 1 gang box so it is right below the panel. Then down the road if I wanted, I could have Romex run from the sub panel up the wall cavity across the attic space of the garage and down the other wall of the garage for another EVSE if I become a 2 EV household. All that would need to be done is make sure the breakers are swapped out in the sub panel for two 40A ones which could feed two EVSE's at 32A?

If they wouldn't run anything else but just the flush mount panel. Could a competent electrician be able to connect to the panel and run a foot or two of #4 Romex in the wall directly down below the panel while only making a small cut in the drywall, like the size that would be covered/hidden by the Tesla wall connector EVSE? I don't mind if it's a crappy patch job or anything as long as my equipment could cover it.

Yes.

Again, based on what little we know at this time.

IF the 100a wiring terminated in a box of some sort in a standard 16-24" wall cavity that is finished with drywall... What an electrician would likely do is cut out an opening the size of the sub-panel. That would give them a place to work and could easily send a 4ga NM-B wire down, up, or through the stud to an adjacent stud cavity where the WC would be mounted. Once they got the wires headed the directions needed, they would pop in the sub-panel and secure it to the studs from the inside.

It would,, of course, be easiest to wire up and over at the same time. But if assembled as stated above, it would be easy to pull the panel, drill up through the plate, and route a wire.

Of course, there are probably lots of approaches.

Get pics before they close it up.

 

[GregD60]

Yes.

Again, based on what little we know at this time.

IF the 100a wiring terminated in a box of some sort in a standard 16-24" wall cavity that is finished with drywall... What an electrician would likely do is cut out an opening the size of the sub-panel. That would give them a place to work and could easily send a 4ga NM-B wire down, up, or through the stud to an adjacent stud cavity where the WC would be mounted. Once they got the wires headed the directions needed, they would pop in the sub-panel and secure it to the studs from the inside.

It would,, of course, be easiest to wire up and over at the same time. But if assembled as stated above, it would be easy to pull the panel, drill up through the plate, and route a wire.

Of course, there are probably lots of approaches.

Get pics before they close it up.

Exactly!

 

[brkaus]

You may as well have two 50A circuits which would each be able to charge at 40A. I believe that if you have 2 Tesla Wall Chargers, you can use power sharing between them. If you do that, I think you just use one higher amperage circuit, like 90A, but I'm not sure how everything is connected in that case.

No, if there was a single 90A breaker protecting two WCs and their 60A wiring, the breaker wouldn't trip if something bad happened and the circuit pulled say 75A.

Either each gets its own 50a-60a breaker (and optionally power share depending on the main panel capacity) or a single 60a goes to two of them and they power share. Even if power sharing 60a, ideally each would get its own 60a breaker per the manual with the WC3. The new universal WC apparently lists that then can be directly connected (as did the WC2 if I recall correctly)

 

[rstx]

Ok, I'm changing my thinking a little. Maybe a flush mount sub panel wouldn't be a deal breaker for me. I really just didn't want anything slapped on the walls like exterior conduit or a box mounted on the wall.

If they did use something like the Square D QO 100 amp flush mount panel. Would that be wired such that a 100A branch circuit was connected to it, likely using 2 AWG. Then could I see if they would run a somewhat short run (like 1.5 feet or something) of #4 Romex in the wall and down from the panel (so same cavity space between studs). Then just ask for like a 1 gang box with a blanked face plate. Mount my wall connector over that 1 gang box so it is right below the panel. Then down the road if I wanted, I could have Romex run from the sub panel up the wall cavity across the attic space of the garage and down the other wall of the garage for another EVSE if I become a 2 EV household. All that would need to be done is make sure the breakers are swapped out in the sub panel for two 40A ones which could feed two EVSE's at 32A?

If they wouldn't run anything else but just the flush mount panel. Could a competent electrician be able to connect to the panel and run a foot or two of #4 Romex in the wall directly down below the panel while only making a small cut in the drywall, like the size that would be covered/hidden by the Tesla wall connector EVSE? I don't mind if it's a crappy patch job or anything as long as my equipment could cover it.

The point of having a subpanel is you can have multiple circuits that source from that panel. So just think about how you would run future circuits from the subpanel to other locations.

In my case I only ran a single 6/2 MC on a 60 amp circuit but I left a service loop in the attic space if later I wanted to use a surface box in the attic and polaris connector to split the 60A circuit to two wall connectors.

 

[Eric33432]

YES to most of the latest responses.

Just let your homebuilder's electrician install the 100 amp circuit/feeder. Once that is installed you can either connect it directly to your Tesla Wall Connector (with pigtails as has been previously discussed) or install a small sub panel which can have a circuit to your TWC and later another TWC or a 14-50 receptacle for another EV.

It is likely that a small sub panel will actually be easier and not that more expensive to install.

Just let them do the job you are paying them for.

 

[acarney]

Just let them do the job you are paying them for.

I've had great confidence in this builder for everything except for this. I think they build good tight homes and have heard good recommendations from friends and others in town... but I am clearly an outlier when it comes to the EV option they have.

The sales agent initially send me a picture of a NEMA 14-50 saying that was their EV Pre Wire... which I was very surprised required a service upgrade past 200A.

A building manager that I talked to when finalizing the plans and any additions that I made said it would be a 100A circuit just capped off.

The onsite construction manager when I did my electric pre-job walk through confirmed the same 100A to a capped box... but when I asked if it would include 2 hot, 1 neutral, and a ground, he was uncertain and said he would have to ask his electric sub when he did the walk through with that person, I think this coming Thursday. He also wasn't sure exactly what it would be when it came to wire size etc.

So... I think the only straight answer I'll get from them about exactly what this is, is from the electrician the problem is, owners usually aren't included in on that meeting, since we go around with the onsite construction manager a few days before and the low voltage guy. It's at that walk through they explain where switches will be and any additional outlets I've added etc. Then that gets communicated to the people actually doing the work.

Again, I'm hoping I can get included in on the electric sub's walk through so I can ask some questions and answer some. I suspect they would be able to clear everything up for me within minutes and get an idea for exactly what I'm looking to do. (Heck, this person might not have seen an EVSE installed if they just have been working with this builder for the last few years in my area so they might know not even know exactly how the end use is wired up/mounted).

That's a good point about asking if I can get in before the drywall is put up. I'll reach out to the sales agent and ask for that. These guys move quick, so I'm hoping they're not coming in right behind the electric work and dry walling the same day or something. I don't want to slow down any work since I'm already predicted to get close to when my rate lock expires and I'm locked a full percentage point or more under what today's rates are. I've got like 15 days wiggle room but that seems scary to me, if I cause them to get behind a week or something because they move to one of the next five homes that are JUST a little behind mine and THEN circle back to drywall mine... I'll be really stressed.

 

[brkaus]

Usually they won't let you mess with anything before drywall. I'd just get photos of the framing before it's closed up. It might help an electrician.

 

[Eric33432]

I've had great confidence in this builder for everything except for this. I think they build good tight homes and have heard good recommendations from friends and others in town... but I am clearly an outlier when it comes to the EV option they have.

The sales agent initially send me a picture of a NEMA 14-50 saying that was their EV Pre Wire... which I was very surprised required a service upgrade past 200A.

A building manager that I talked to when finalizing the plans and any additions that I made said it would be a 100A circuit just capped off.

The onsite construction manager when I did my electric pre-job walk through confirmed the same 100A to a capped box... but when I asked if it would include 2 hot, 1 neutral, and a ground, he was uncertain and said he would have to ask his electric sub when he did the walk through with that person, I think this coming Thursday. He also wasn't sure exactly what it would be when it came to wire size etc.

So... I think the only straight answer I'll get from them about exactly what this is, is from the electrician the problem is, owners usually aren't included in on that meeting, since we go around with the onsite construction manager a few days before and the low voltage guy. It's at that walk through they explain where switches will be and any additional outlets I've added etc. Then that gets communicated to the people actually doing the work.

Again, I'm hoping I can get included in on the electric sub's walk through so I can ask some questions and answer some. I suspect they would be able to clear everything up for me within minutes and get an idea for exactly what I'm looking to do. (Heck, this person might not have seen an EVSE installed if they just have been working with this builder for the last few years in my area so they might know not even know exactly how the end use is wired up/mounted).

That's a good point about asking if I can get in before the drywall is put up. I'll reach out to the sales agent and ask for that. These guys move quick, so I'm hoping they're not coming in right behind the electric work and dry walling the same day or something. I don't want to slow down any work since I'm already predicted to get close to when my rate lock expires and I'm locked a full percentage point or more under what today's rates are. I've got like 15 days wiggle room but that seems scary to me, if I cause them to get behind a week or something because they move to one of the next five homes that are JUST a little behind mine and THEN circle back to drywall mine... I'll be really stressed.

If they say it is a 100 amp circuit, capped off, and you are upgrading to 320 amp service, it seems to me that is very likely what you will get.

Hopefully you can speak with the electrician, but you should be OK.

 

[GregD60]

No, if there was a single 90A breaker protecting two WCs and their 60A wiring, the breaker wouldn't trip if something bad happened and the circuit pulled say 75A.

Either each gets its own 50a-60a breaker (and optionally power share depending on the main panel capacity) or a single 60a goes to two of them and they power share. Even if power sharing 60a, ideally each would get its own 60a breaker per the manual with the WC3. The new universal WC apparently lists that then can be directly connected (as did the WC2 if I recall correctly)

You got me wondering how the sharing worked, so I looked it up, and you are correct that each wall charger should have its own 60 amp circuit to allow optimal Tesla charging. A 100A subpanel with two or more 60A circuits coming from it would allow for this. One of the examples they use in the manual is a 100A subpanel with 3 60A circuits feeding 3 Tesla Wall Chargers. The info is in the wall charger installation manual - https://www.tesla.com/sites/default...ng/Gen3_WallConnector_Installation_Manual.pdf

It says, "The firmware-based power sharing feature enables up to 6 Wall Connectors installed at the same site to intelligently share the site's total available power via unit-to-unit Wi-Fi." and "See below for examples of Wall Connector power sharing diagrams (one with sub-panel and one without). Each individual Wall Connector in below examples is capable of providing 48 amps when it is the only one in use. As more Wall Connectors begin plugging into vehicles, the system will automatically distribute power based on the total power allocated to the site."

 

[Eric33432]

The onsite construction manager when I did my electric pre-job walk through confirmed the same 100A to a capped box... but when I asked if it would include 2 hot, 1 neutral, and a ground, he was uncertain and said he would have to ask his electric sub when he did the walk through with that person, I think this coming Thursday. He also wasn't sure exactly what it would be when it came to wire size etc.

They will very likely install 4 wires, but you should know that it is not a violation of the NEC to install a small sub panel if you only have 3 wires (2 hots and 1 ground) if all the loads served by the sub panel are 240 volt 2 wire loads, as is the Tesla Wall Connector.

I have such a sub panel for three 240 volt air conditioner circuits at my house.

But that may not be allowed by your local inspector. The concern your AHJ may have is that someday someone will add a 120 volt circuit using the ground wire as the neutral. In that event the AHJ might allow it if you permanently label the panel with a placard that says "NO NEUTRAL-240 VOLT LOADS ONLY" or wording to that effect.

If they are installing a 100 amp circuit for the EV, and upgrading to 320 amp service, I would be really surprised if they connect this 100 amp circuit to the load center for all the home's other circuits unless that load center is a 400 amp panel. But 400 amp panels are very expensive, the normal way this is done is by feeding 200 amp or less panels from a meter-main. For example, in my house I have three 200 amp panels fed from my 600/480 amp service. In your case I would expect a 200 amp feed to the load center for the home's regular circuits, and 100 amp from the meter for your EV circuit. To do it any other way would defeat the purpose of upgrading to the 400/320 amp service.

Regarding the wire size, if it is a 100 amp service it has to be at least #3 CU or #1 AL, both of which are too large to fit into the Tesla Wall Connector.

I would really advise you to let them install the 100 amp circuit which you or someone will really appreciate. If not now, in 5, 10, or 20 years.

 

[acarney]

So even though the onsite manager told me to show up at 8am, the electricians got there at 7am and already had a lot of the rough in wiring done already. I ultimately just left them do their thing and I think it'll work out.

They ran 2 AWG copper wire to what looks like will be a flush mount box. It has a 100 amp breaker in the panel. I'll probably see if I can replace the box with a small sub panel so I can make use of the 100 amps and 2 AWG wire to that location. Then I think there is enough room to the left of the box to mount my wall connector (since it's a small profile and needs to mount to a stud) and I'm hoping because it'll be in the same wall cavity it will be relatively easy to run a foot or less of 4 AWG copper to the wall connector and toss a 60 amp breaker in the sub panel.

If down the road I want to add a second EVSE I will have 40 amps of room in the sub panel and they could run something up that wall into the attic space and over to somewhere else in the garage and I could feed that vehicle with 32 amps (7.7kW). I don't foresee myself having a second EV any time soon, but maybe 5 to 10 years down the road.

 

[acarney]

 

[GregD60]

So even though the onsite manager told me to show up at 8am, the electricians got there at 7am and already had a lot of the rough in wiring done already. I ultimately just left them do their thing and I think it'll work out.

They ran 2 AWG copper wire to what looks like will be a flush mount box. It has a 100 amp breaker in the panel. I'll probably see if I can replace the box with a small sub panel so I can make use of the 100 amps and 2 AWG wire to that location. Then I think there is enough room to the left of the box to mount my wall connector (since it's a small profile and needs to mount to a stud) and I'm hoping because it'll be in the same wall cavity it will be relatively easy to run a foot or less of 4 AWG copper to the wall connector and toss a 60 amp breaker in the sub panel.

If down the road I want to add a second EVSE I will have 40 amps of room in the sub panel and they could run something up that wall into the attic space and over to somewhere else in the garage and I could feed that vehicle with 32 amps (7.7kW). I don't foresee myself having a second EV any time soon, but maybe 5 to 10 years down the road.


View attachment 996812

It sure would be nice if they'd let you bring your electrician in now, before the drywall is installed. If it were me, I'd probably wait until the electrician is done, and then before the drywallers come in, just install the subpanel and box myself.

 

[acarney]

It sure would be nice if they'd let you bring your electrician in now, before the drywall is installed. If it were me, I'd probably wait until the electrician is done, and then before the drywallers come in, just install the subpanel and box myself.

The home isn't fully custom, the builder explicitly bans me from being on the property without a representative from the builder there (they claim due to liability, I can see where that makes sense). I won't actually own the home until I close on it in March.