EVSE Conductor Size

Jhenson29

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The below is USA specific.

I'll lead with my question:
Does anyone know what size conductors Clipper Creek uses in their 80 amp J1772 Cable?

Story below:
I purchased an 18kW Wall Wattz (240VAC / 75 A). For hardwiring, it comes with 6 foot of LFNC with 6 AWG THHN wires for connection to a 100-amp breaker.

https://wattzilla.com/products/wall-wattz.htm

I called them today to question the wire size as it seems small. They guy told me it doesn't need to be any bigger because that's the size of the wires in the cable [for the J1772 plug]. He said the 6 AWG is good for 99 amps and the unit is UL tested as is. I can't open it to replace the feed wires without voiding the warranty.

He put me in touch with the principal engineer he worked with at UL. This guy directed me to NEC Table 400.5(B) which shows that 6 AWG is good for 99 amps if it's only two current carrying conductors. Okay. But I have two issues. One I pressed him on and one I didn't.

The first is temperature derating. 400.5(B) is listed at 30°C (86°F). There's no further temperature derating information in 400 so it should default to Table 310.16. I questioned him about ambient temperature and derating with 310.16. Given this is an EVSE and I would expect higher ambient temperatures are a reasonable consideration. He told me all EVSEs should be rated to 50°C (122°F). The Wattzilla guy was still on the line with us and chimed in that they actually have a higher rating, but didn't state what that is. But generally, the UL guy more or less blew me off on this. I went back to check later and going by 50°C, that would put the derating at 0.82. So, it's around 81 amps. It may be okay, but it still seems marginal.

The second issue (that I didn't get to because I didn't think about it at the time) is that Article 400 is for flexible cords and cables, which the LFNC feeding the unit is not. I believe this would just fall under 310.16 (in a raceway with 3 or less current carrying conductors) and then I'm looking at 75 amps for the 6 AWG THHN before temperature derating. It's 61 amps at 50°C. Although, for my area, even in a garage, the next lower temperature range is more reasonable with a derating of 0.87 which is 65 amps.

The second issue is really what I was calling them about because of my concern for the 6 AWG feed wires. The electrician I have quoted running something larger to the unit, but that was before I found out I'm not allowed to open it up. I'm not sure what to do now other than install as is.
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Jhenson29

Jhenson29

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I’m also curious if anyone knows if there is another section in the NEC that would apply to EVSE feeds.
 

F16HTON

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Please state your actual concern and I will reply with specifics. I am assuming that you have concerns regarding the conductor sizing of the 18K Wall Watz and that you suspect that both the supply cable and the flexible charging cable are underrated? It that correct?

NECA 413-2019 Standard for Installing and Maintaining Electric Vehicle Supply Equipment (EVSE) is the reference manual that you can refer to. You will also need to check with both your local building codes and the utility provider codes too.

Here is a link to the local codes. https://www.stlouis-mo.gov/government/departments/public-safety/building/building-codes.cfm
 
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Jhenson29

Jhenson29

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Please state your actual concern and I will reply with specifics. I am assuming that you have concerns regarding the conductor sizing of the 18K Wall Watz and that you suspect that both the supply cable and the flexible charging cable are underrated? It that correct?
Mostly that the supply cable is undersized.

Edit: but I’m also curious about the cable conductor size compared to other similar amperage EVSEs.
 

F16HTON

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Mostly that the supply cable is undersized.

Edit: but I’m also curious about the cable conductor size compared to other similar amperage EVSEs.
Supply cable is going to depend on they length of the run from the main panel to the sub panel and the sub panel to the actual charging unit. Have you discussed this with the electrical contractor that will be conducting the installation?

IMO limit the length of the run from charging unit to the sub-panel disconnect as much as possible and ensure that the run from the main panel to that sub-panel is adequately rated for that length of run and the appropriate conduit sizing has been selected.
 


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Jhenson29

Jhenson29

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Supply cable is going to depend on they length of the run from the main panel to the sub panel and the sub panel to the actual charging unit. Have you discussed this with the electrical contractor that will be conducting the installation?

IMO limit the length of the run from charging unit to the sub-panel disconnect as much as possible and ensure that the run from the main panel to that sub-panel is adequately rated for that length of run and the appropriate conduit sizing has been selected.
Sorry, not from the main to the sub panel. That’s not an issue.

My question is about the branch circuit from the sub panel to the EVSE. It’s 6 AWG THHN in LFNC used for 75 amps.
 

F16HTON

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What diameter is the LFNC? 6 AWG copper is good up to 100 amps if in free air. I'd be concerned about the conduit size.
 
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Jhenson29

Jhenson29

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What diameter is the LFNC? 6 AWG copper is good up to 100 amps if in free air. I'd be concerned about the conduit size.
I’ll have to go check. I think it was 1” but it may have been 3/4”. But either way, that’s a raceway, not free air.

Edit: I checked and it’s 1”.

Unless there are exceptions for either length or use called out somewhere?
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