Tesla charging station

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sunbear

Member
Location
New Jersey
Occupation
Engineer
I've spoken to 3 electricians in my area in New Jersey about this so far, two of them were even on tesla's list of electricians who have passed the tesla training for installing chargers. So far, all of them are of the opinion that 6 AWG romex suffices for running the charger at its full 48A and that a direct lookup in NEC table 310.15 (B) (16) with no adjustment is all that is required to determine a suitable wire gauge.

I have even directly pointed out Section 210.19(A)(1) but they all think there is no need to multiply the 48A by 125% when considering ampacity of the conductors (i.e. 100% is sufficient). I've even pointed out Section 625.42 explaining that a EV charger is considered a continuous load. Nothing convinces them.

Is Section 210.19(A)(1) some super-obscure section, of little practical relevance, that only 5% of electricians and inspectors even know about, let alone understand, or do you think I've just been unlucky so far and I need to keep searching for a better educated electrician to install the charger?

What if any danger is there with using 6 AWG romex in this application? Some of these electricians claim they have already installed 6 AWG romex in over a hundred installations.

I intend to fill the walls around the wire with closed-cell spray foam, so I would expect that any heat build-up during charging would not quickly dissipate.

Sure, I could just select one of these electricians and insist they use 4 AWG romex, or some sort of 6 AWG 90C rated wire (perhaps THWN-2 ?), but I am wondering should I even use an electrician who doesn't understand code? What do you think?

 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
It's really no mystery. 48*125%= 60 amps. #6 AWG NM cable is only good for 55 amps so it's too small. Use MC cable or conduit and wire and #6 is good for 65 amps.
 

suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
It would help if the nameplate info had the 125% factor in it. Ask these same electricians how they would wire a strip heater that says it is 9600 watts. The MCA on that heater would be 50A even though the load is 40A. It needs 50A wire and breaker.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
It's really no mystery. 48*125%= 60 amps. #6 AWG NM cable is only good for 55 amps so it's too small.
Too small to satisfy 210.19(A)(1), but as far as I can see, not too small to be safely used in this application. 210.19(A)(1) should just be deleted, as 210.20(A) plus 240.4 is sufficient.

Cheers, Wayne
 

sunbear

Member
Location
New Jersey
Occupation
Engineer
It's really no mystery. 48*125%= 60 amps. #6 AWG NM cable is only good for 55 amps so it's too small. Use MC cable or conduit and wire and #6 is good for 65 amps.
My garage is currently unfinished. I asked one of the electricians about installing THWN-2 in conduit and he said that it would be "too much work" to run EMT inside the wall through holes in the garage studs. It would be about a 20 foot run up from the electrical box, around the side door and down the other side (so two or three 90 degree bends).

Another electrician suggested using smurf-tube. Is that code compliant for the purpose of housing THWN cable?

I don't see "MC" mentioned in Table 310.16 here so I'm not sure how one would determine if the rating is sufficient or not. But it looks more flexible and easier to install than EMT with THWN inside.

Do you have any specific MC cable you know for sure would be good for running a Tesla charger at the full capacity?
Preferably steel clad rather than aluminum since it is less likely to be punctured by someone carelessly shooting a nail gun while redoing the siding 10 years from now.
 

sunbear

Member
Location
New Jersey
Occupation
Engineer
Too small to satisfy 210.19(A)(1), but as far as I can see, not too small to be safely used in this application. 210.19(A)(1) should just be deleted, as 210.20(A) plus 240.4 is sufficient.

Cheers, Wayne
It's good to know that there's no safety issue for the sake of all the other customers who now have #6 romex installations.

I'm planning to install my Tesla charger in the next month so I can't want to wait for a change to the code that is unlikely to happen. I'd prefer the installation to be code compliant (as the code is written now) and if that means that the wire also has some additional amperage headroom, that's not a bad thing since it's not unlikely that EV chargers with higher amps will become even more commonplace in the future. In fact the gen 2 tesla charger had a capacity of 80A compared to gen3 which only has 48A!
 
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Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
My garage is currently unfinished. I asked one of the electricians about installing THWN-2 in conduit and he said that it would be "too much work" to run EMT inside the wall through holes in the garage studs. It would be about a 20 foot run up from the electrical box, around the side door and down the other side (so two or three 90 degree bends).

Another electrician suggested using smurf-tube. Is that code compliant for the purpose of housing THWN cable?

I don't see "MC" mentioned in Table 310.16 here so I'm not sure how one would determine if the rating is sufficient or not. But it looks more flexible and easier to install than EMT with THWN inside.

Do you have any specific MC cable you know for sure would be good for running a Tesla charger at the full capacity?
Preferably steel clad rather than aluminum since it is less likely to be punctured by someone carelessly shooting a nail gun while redoing the siding 10 years from now.
FMC is an option thru the studs too, and then pulling in the THHN.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
My garage is currently unfinished. I asked one of the electricians about installing THWN-2 in conduit and he said that it would be "too much work" to run EMT inside the wall through holes in the garage studs. It would be about a 20 foot run up from the electrical box, around the side door and down the other side (so two or three 90 degree bends).

Another electrician suggested using smurf-tube. Is that code compliant for the purpose of housing THWN cable?

I don't see "MC" mentioned in Table 310.16 here so I'm not sure how one would determine if the rating is sufficient or not. But it looks more flexible and easier to install than EMT with THWN inside.

Do you have any specific MC cable you know for sure would be good for running a Tesla charger at the full capacity?
Preferably steel clad rather than aluminum since it is less likely to be punctured by someone carelessly shooting a nail gun while redoing the siding 10 years from now.
If you want to use #6 AWG conductors you need a wiring method that can utilize their 75° C ampacity. MC cable, SE cable, or conduit (EMT, FMC, ENT, etc.) and wire can use the 75° C ampacity. NM cable cannot due to 334.80 which limits it to 60° C.
 

Jon456

Senior Member
Location
Colorado
if that means that the wire also has some additional amperage headroom, that's not a bad thing since it's not unlikely that EV chargers with higher amps will become even more commonplace in the future.
With that in mind, you probably should lean towards installing conduit and even oversizing the conduit so larger conductors can be installed in the future.
 

sunbear

Member
Location
New Jersey
Occupation
Engineer
With that in mind, you probably should lean towards installing conduit and even oversizing the conduit so larger conductors can be installed in the future.
Would ENT (smurf tube) be sufficient as a conduit or would a EMT be required. I am thinking that a continuous load of 48A running though wires encased in closed cell foam for 6 hours will likely cause the temperature inside the conduit to exceed 50C. Isn't 50C is the limit for ENT?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Would ENT (smurf tube) be sufficient as a conduit or would a EMT be required. I am thinking that a continuous load of 48A running though wires encased in closed cell foam for 6 hours will likely cause the temperature inside the conduit to exceed 50C. Isn't 50C is the limit for ENT?
The 50° C limit is for ambient temperature outside of the conduit. I don't see an issue with using #6 AWG conductors. If it concerns you then you can use larger conductors.
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Would ENT (smurf tube) be sufficient as a conduit or would a EMT be required. I am thinking that a continuous load of 48A running though wires encased in closed cell foam for 6 hours will likely cause the temperature inside the conduit to exceed 50C. Isn't 50C is the limit for ENT?
Thus my suggestion for FMC or Flex. Not sure of temperature rating of ENT, but do know there are a couple of differently rated ENT. There is the orange (innerducting) that is used almost strictly for LV. Then there is the blue that I've seen used for both 600V and LV.
Only conditional for FMC would be length limitation for use as the EGC, if longer run it needs an added conductor. But if considering ENT you would use one anyway.
 
Not really as I don't have any data for a technical substantiation to support such a change. without such data the it is very likely the PI will be resolved (rejected) at the first draft meetings.
Funny how the CMP's make code changes all the time without data or a history of problems, but when we try to get a code deleted or changed they say "oh there's no data to support that change". The whole organization and process is very incompetent and dysfunctional.
 

Jon456

Senior Member
Location
Colorado
Would ENT (smurf tube) be sufficient as a conduit or would a EMT be required. I am thinking that a continuous load of 48A running though wires encased in closed cell foam for 6 hours will likely cause the temperature inside the conduit to exceed 50C. Isn't 50C is the limit for ENT?
I don't get it. In an earlier post you state that you'd prefer steel flex instead of aluminum to protect against nails. Now you're asking about using smurf. 🤔

Personally, I'd use EMT.
 

DH Electric Co

Electrons, Chess, Bacon & Broads.
Location
Addison, IL
Occupation
Electrician
I don't get it. In an earlier post you state that you'd prefer steel flex instead of aluminum to protect against nails. Now you're asking about using smurf. 🤔

Personally, I'd use EMT.
I like the Chicago area & suburbs.............everything is in steel conduit. We don't have to do all those calculations and figure out wiring methods [ie: romex, SE, etc] Just run the conduit & install the wire per code [ie: wire fill & derating values]
 

sunbear

Member
Location
New Jersey
Occupation
Engineer
I don't get it. In an earlier post you state that you'd prefer steel flex instead of aluminum to protect against nails. Now you're asking about using smurf. 🤔

Personally, I'd use EMT.
I mentioned the reason earlier. The electrician said it was too difficult to install EMT since it would involve two to three 90 degree turns and passing between holes in studs. I want the wire and conduit hidden inside the wall before foam insulating and sheet rocking. Is it really that difficult or is he exaggerating?

For this reason I am considering alternatives such as flexible conduit, FMC, or even no conduit NM 3 conductor 4 awg like this
 
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Jon456

Senior Member
Location
Colorado
I mentioned the reason earlier. The electrician said it was too difficult to install ENT since it would involve two to three 90 degree turns and passing between holes in studs. I want the wire and conduit hidden inside the wall before foam insulating and sheet rocking. Is it really that difficult or is he exaggerating?

For this reason I am considering alternatives such as flexible conduit, FMC, or even no conduit NM 3 conductor 4 awg like this
Without seeing the actual existing construction, it's impossible to make an accurate determination on installation difficulty. But considering this is an unfinished garage, it should not be too difficult to install EMT. There is nothing that requires a bend to be made in the middle of a 10 foot stick of conduit. In other words, a 90 degrees bend can be joined to straight runs with connectors.

If you intend to fill the wall cavities with foam-in-place insulation, then I double-down on the recommendation to install conduit.
 

sunbear

Member
Location
New Jersey
Occupation
Engineer
Without seeing the actual existing construction, it's impossible to make an accurate determination on installation difficulty. But considering this is an unfinished garage, it should not be too difficult to install EMT.

Here's a picture of my garage with the likely path (in red) that conduit would take in order to be hidden after sheet rocking.
The charger would be mounted in the corner next to the garage door
ConduitPathCleaned.JPG
 
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