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Wire size for wall charger

Rocky_H

Well-Known Member
Feb 19, 2015
7,271
8,957
Boise, ID
Are you sure? I read the load calculation rules as using nameplate rating for hardwired devices, which would be 48A. The 125% derating on top of that is to account for said 48A being a continuous load.
That is what I recall seeing as well. For load calculations, I think you do use the continuous current amount, which would be 48A.
 
That is what I recall seeing as well. For load calculations, I think you do use the continuous current amount, which would be 48A.

Per the 2017 NEC, the rating of the load would be the load that the EV charging system allows, not the rating of the branch circuit overcurrent protection. Since the wall charger manages the maximum load, to me that would equate to the load management system and would dictate the "maximum equipment load".

Excerpt from the EV Charging article of the code (2017 NEC):
upload_2021-2-12_20-43-42.png
 
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mcorf

Member
Apr 21, 2019
278
139
Campbell,Ohio
Any updates, mcorf?

Tim
Just that they were checking with their inspectors because according to them everything was given the OK before they installed mine. They said because mine was the 1st they ever did they checked it out ahead of time. They are checking everything very carefully as they said they have installed 8 more since mine with the same wire. Where can I get something in writing to show them and their inspector ?
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,271
8,957
Boise, ID
Just that they were checking with their inspectors because according to them everything was given the OK before they installed mine. They said because mine was the 1st they ever did they checked it out ahead of time. They are checking everything very carefully as they said they have installed 8 more since mine with the same wire. Where can I get something in writing to show them and their inspector ?
Sure. Something in writing to show them. It's the basic table of the amp rating for wire types at certain temperature ratings that are found all over the place. It's called an "ampacity table". You can find dozens of them. Here's the first one that comes up on Google, and it's a little more helpful and readable because some of the others just have the temperature rating columns, but this one also includes in each column the wire or cable types that are included for that temperature rating, which is super helpful:

Ampacity Charts - Cerrowire

Here's how to read it. The cable type they used is called "Romex" or "NM-B"--same thing. See where NM-B is listed in that first column in the 60 degree Celsius rating? That's the column you have to use for the cable that they installed. If you go down to the 6 gauge, under the 60 degree C column, it says 55. That is a maximum of a 55A rated circuit that can be used with 6 gauge Romex cable. They have this installed and configured as a 60A circuit, which is greater than the 55A limit, so it is not allowed.

Man! This isn't even a complicated one; they should not be having this trouble.
 
Just that they were checking with their inspectors because according to them everything was given the OK before they installed mine. They said because mine was the 1st they ever did they checked it out ahead of time. They are checking everything very carefully as they said they have installed 8 more since mine with the same wire. Where can I get something in writing to show them and their inspector ?
mcorf, as Rocky mentioned, it comes down to the ampacity of the selected cable based on the cable type and its effective insulation rating (in terms of *C). Since you are in Ohio, your state has adopted the 2017 version of the National Electrical Code (NFPA 70).

As Rocky mentioned, the wire used (typical in most residential homes) is type NM (Nonmetallic-Sheathed Cable as defined in Article 334) and is only rated for 60*C, so at #6AWG it is rated 55A. This comes from table 310.15(B)16 in Article 310 of the NEC clipped below:
upload_2021-2-15_20-43-38.png


Section 240.4(B) of the code DOES allow the installer to utilize the next higher standard size breaker based on the ampacity of the cable as long as they follow several rules. Based on your installation they CAN protect the cable with a 60A breaker as installed (with 55A cable). See below:
upload_2021-2-15_20-51-47.png



The problem with your basic installation is that the charger is designed for a maximum full load amperage of 48A. Per Article 625 (EV chargers) of the code, the load is to be considered continuous which requires 125% rating to the conductors (cables) based on the full load in amps it would need (i.e. 1.25 x 48A = 60A). This means that the conductors (cables) need to have a minimum ampacity value of 60A (not 55A).

Hopefully this can help give you specific guidance and code articles for them to reference. If you need more, I can send you a private message of more code clips if really needed, but I don't want to stretch my limits here on posting copyrighted information which I have paid to use.

Good luck!
 

spat12

Member
May 20, 2021
38
40
New Jersey
Yes. It's not up to code. jcanoe has the correct guidance here.

For clarity on why 48A charging is not okay: a circuit must be derated by 20% for continuous draws, including car charging. So that 55A wire is not acceptable because 80% of that is 44A. That's the number you can't exceed, per code. There's no setting in the HPWC for 55A circuit, so 50A is the safe setting, and ideally the breaker should be changed to match this. Otherwise, if you really need a 60A circuit for 48A charging, the wire has to be made 4AWG NM-B or else 6AWG THHN in conduit (or similar).

Hi,
I am planning to install HPWC Gen 3 planning to use 60amp breaker. I am going to bring cable from side of circuit panel (i.e. through stud where panel is installed) and HPWC will be installed on very next stud 16" apart. Do I need to run THHN cable through conduit behind drywall? Does ground THHN cable also needs to be 6 AWG?
Thank You.
 

MN-MS100D

Member
Dec 10, 2018
150
117
Minnesota
Hi,
I am planning to install HPWC Gen 3 planning to use 60amp breaker. I am going to bring cable from side of circuit panel (i.e. through stud where panel is installed) and HPWC will be installed on very next stud 16" apart. Do I need to run THHN cable through conduit behind drywall? Does ground THHN cable also needs to be 6 AWG?
Thank You.
THHN needs to be run in a raceway. Grounding conductor can be #10 if you plan to use one.
 

TBrownTX

Member
Dec 25, 2020
961
1,131
Dallas, TX
If you choose to use Romex (does not require conduit in-wall) make sure and use #4 versus #6 due to the lower temperature rating of the wire.

It includes a ground, however if you go with 4/3 versus 4/2 you can use the extra wire as a ground, and would be able to covert to a 14-50 later.

Tim
 
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DonaldBecker

Member
Aug 24, 2020
155
180
95033
Hi,
I am planning to install HPWC Gen 3 planning to use 60amp breaker. I am going to bring cable from side of circuit panel (i.e. through stud where panel is installed) and HPWC will be installed on very next stud 16" apart. Do I need to run THHN cable through conduit behind drywall? Does ground THHN cable also needs to be 6 AWG?
Thank You.

Reconsider running the wiring out from the side of the load center that is against the stud.
You will need to clamp NM cable or attach the conduit, which means drilling an extra-large hole centered on the knock-out.
It's more common to run the wiring from the top or bottom and then through a hole centered on the stud. With all of those turns, NM cable is usually easier to install.

With that short of a distance you aren't going to be spending a lot on copper. Use the largest wire that the devices (circuit breaker and EVSE) support. You don't have a choice with NM-B, but with THHN the grounding conductor (green ground wire) can be 10 AWG for up to 60 amps, and 8 AWG up to 100 amps. 10 AWG looks small next to 6 AWG and the distance is short, so you might consider using 8 AWG solely so that the inspector doesn't need to double check.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
7,271
8,957
Boise, ID
Hi,
I am planning to install HPWC Gen 3 planning to use 60amp breaker. I am going to bring cable from side of circuit panel (i.e. through stud where panel is installed) and HPWC will be installed on very next stud 16" apart. Do I need to run THHN cable through conduit behind drywall? Does ground THHN cable also needs to be 6 AWG?
Thank You.
When it's all inside the wall like that, you generally don't use individual wires in conduit.
If you choose to use Romex (does not require conduit in-wall) make sure and use #4 versus #6 due to the lower temperature rating of the wire.

It includes a ground, however if you go with 4/3 versus 4/2 you can use the extra wire as a ground, and would be able to covert to a 14-50 later.
Yeah, that's what NM-B cable is intended for--running directly in walls. You would need to use 4 gauge cable for the 60A circuit, though. Check this ampacity table for reference:
The 6 gauge is only allowed up to 55A, so you do need 4 gauge.

It's going to take a little drywall work. You'll have to cut a square of it off the wall that spans across those studs. And you'll have to drill through the stud from the side to put the cable through. And then you'll have to screw your square of drywall back in and tape it. But then it will be a pretty clean look.
 
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jcanoe

Active Member
Oct 2, 2020
4,334
4,499
Maryland
When it's all inside the wall like that, you generally don't use individual wires in conduit.

Yeah, that's what NM-B cable is intended for--running directly in walls. You would need to use 4 gauge cable for the 60A circuit, though. Check this ampacity table for reference:
The 6 gauge is only allowed up to 55A, so you do need 4 gauge.

It's going to take a little drywall work. You'll have to cut a square of it off the wall that spans across those studs. And you'll have to drill through the stud from the side to put the cable through. And then you'll have to screw your square of drywall back in and tape it. But then it will be a pretty clean look.
Would there need to be a kick plate added over the outward facing side of the stud where the NM-B penetrates the stud to protect the wire from an errant nail or screw?
 

Rocky_H

Well-Known Member
Feb 19, 2015
7,271
8,957
Boise, ID
Would there need to be a kick plate added over the outward facing side of the stud where the NM-B penetrates the stud to protect the wire from an errant nail or screw?
That may be very true. I'm not sure what those requirements are. I hate the idea of having to do that drywall stuff, so I'm going to avoid going sideways through my wall when I switch from my 14-50 to wall connector. I'll just come out of the wall and use flex metal conduit.
 

MY-Y

Active Member
Mar 4, 2020
1,229
1,403
MD
Personally, I'm glad I cut and repaired my drywall. It was only a couple of hours of work, now it looks great. Garage paint is often flat white, which is very forgiving to a novice mud job.

The 4-3 is a pain to pull through the studs. Having the proper wire on my HPWC and the ability to swap the spare 14-50 with an additional HPAC later sure is nice though.
20200526_191106.jpg

20210521_145356.jpg
 
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spat12

Member
May 20, 2021
38
40
New Jersey
When it's all inside the wall like that, you generally don't use individual wires in conduit.

Yeah, that's what NM-B cable is intended for--running directly in walls. You would need to use 4 gauge cable for the 60A circuit, though. Check this ampacity table for reference:
The 6 gauge is only allowed up to 55A, so you do need 4 gauge.

It's going to take a little drywall work. You'll have to cut a square of it off the wall that spans across those studs. And you'll have to drill through the stud from the side to put the cable through. And then you'll have to screw your square of drywall back in and tape it. But then it will be a pretty clean look.
Thank You all for quick and valuable advise; appreciated.
 

TBrownTX

Member
Dec 25, 2020
961
1,131
Dallas, TX
Personally, I'm glad I cut and repaired my drywall. It was only a couple of hours of work, now it looks great. Garage paint is often flat white, which is very forgiving to a novice mud job.

The 4-3 is a pain to pull through the studs. Having the proper wire on my HPWC and the ability to swap the spare 14-50 with an additional HPAC later sure is nice though.

Did the same thing here.

IMG_1868.jpeg


IMG_2009.jpeg
 

spat12

Member
May 20, 2021
38
40
New Jersey
DonaldBecker in post 93 said - Reconsider running the wiring out from the side of the load center that is against the stud. I am planning exact similar installation as yours. Looks like you have ran your cable from side of load panel. Did you use NM or THHN in conduit?
Thanks
 

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