-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Wire size for wall charger
- Thread starter bbwex
- Start date
That is what I recall seeing as well. For load calculations, I think you do use the continuous current amount, which would be 48A.
Magnetic Flux
Member
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):
TBrownTX
Active Member
mcorf
Member
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.
I know, right? I'm amused with the idea of giving this explanation to a licensed electrician or inspector, seeing as it's likely to come off as condescending to describe one of the most basic calculations...
Magnetic Flux
Member
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:
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:
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!
@Magnetic Flux I'll bet it's that "next size up" that is causing their brain lapse. Someone had heard of it but misunderstands how it works. They think they use 55A rated wire and then get to use a 60A breaker, and then they think [snaps fingers] PRESTO! The whole thing is now 60A rated, right? NO!
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
Active Member
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
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
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.
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:
Cerrowire Resources - Ampacity Charts
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com
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?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.Cerrowire Resources - Ampacity Charts
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
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.
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.
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.
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.
Last edited:
Thank You all for quick and valuable advise; appreciated.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.Cerrowire Resources - Ampacity Charts
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
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.
TBrownTX
Active Member
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
Similar threads
- Question
