NM Cable Sizing for Ford F-150 Lightning Charging Station

[paullmullen]

I was watching a video of a well-known electrician doing an installation of the Ford Charge Station Pro. The charger is rated at 80A and since charging can often take more than 3 hours, it is a continuous load. Thus, the branch circuit should be sized for 80A x 1.25 = 100A.

The demonstrated installation was completed using 3AWG NM Cable. Per 344.80, "the allowable ampacity shall not exceed that of a 60-degree C rated conductor."

The installer showed that the cable was rated at 90-degrees C (NM-B) and evidently the connectors are also rated at 90-degrees.

At 90-degrees, the ampacity of 3AWG cable is 115A, but it is only 85A at 60-degrees C.
At 60-degrees, the ampacity of 1AWG cable is 110A.
(From Ampacity tables in Article 310.)

I suppose that he may have been using some cable type other than NM, but that's what it looked like and the teacher was not specific.

I assume that he was doing it correctly and I'm missing a finer point. Can someone point it out?

Paul

 

[curt swartz]

NM-B Cable is limited to the ampacities of the 60C column. Also I don't believe there is such a thing as #3 NM cable.

He might have been using #3 SE cable that can use the 75C column.

 

[jaggedben]

I agree with Curt. FWIW in my experience NM has a black sheath and SER has a grey sheath. 2awg NM-B is the biggest it comes and that's only rated for 95A, so it's not possible to use NM for this install. But copper SER would be great.

 

[paullmullen]

He made a point of it being rated for 90-degrees, so I'll keep digging. It really doesn't matter. I just wanted to know if I was thinking clearly.

 

[electrofelon]

The installer showed that the cable was rated at 90-degrees C (NM-B) and evidently the connectors are also rated at 90-degrees.

Even with best-ever-super-duper-unobtainium-suitible-for-use-inside-nuclear-reactor-and-on-turbo-encabulators cable, the terminations would still be rated 75 degrees. I am not aware of any 90 degree terminations on equipment (you can splice @ 90 degrees, but not terminate on equipment or breakers).

 

[letgomywago]

Even with best-ever-super-duper-unobtainium-suitible-for-use-inside-nuclear-reactor-and-on-turbo-encabulators cable, the terminations would still be rated 75 degrees. I am not aware of any 90 degree terminations on equipment (you can splice @ 90 degrees, but not terminate on equipment or breakers).

I thought some fused disconnects were 90°

 

[petersonra]

I think there are a few devices with terminations rated for 90C. Not real common, and usually over 100 amps.

 

[letgomywago]

Still who would want 200° F anything in their house

 

[Fred B]

I've had multiple EVSE that required 90 deg wire and copper only (printed inside of equipment and manual), that eliminates NM and AL-SER as a wiring option.

 

[Fred B]

Still who would want 200° F anything in their house

Toaster, Electric range etc.
Hopefully the incident causing that level of unintended heating will have tripped the breaker before it ever reaches those temperatures on the wire or terminations. When you are getting those higher continuous load values like an EVSE you want that extra safety margin from the 90 deg. wire.

 

[infinity]

I've had multiple EVSE that required 90 deg wire and copper only (printed inside of equipment and manual), that eliminates NM and AL-SER as a wiring option.

Does NM cable have 90° C conductors?

 

[Fred B]

Does NM cable have 90° C conductors?

Not marked and limited to calculation at 60 deg C. per 334.80 even though the requirement of 334.112 for NM-B requires use of 90 deg wire, the cable assembly is only 60 deg due to limits of it heat dissipation ability. So wouldn't consider the assembly to meet the required 90 Deg intent especially with continuous load nature of EVSE.

To even consider use of NM on the lightning charger @ 100A min, the NM would need to be Minimally a #1awg and the terminals size max out a #3awg on the lightning charger and must be copper only

 

[infinity]

Not marked and limited to calculation at 60 deg C. per 334.80 even though the requirement of 334.112 for NM-B requires use of 90 deg wire, the cable assembly is only 60 deg due to limits of it heat dissipation ability. So wouldn't consider the assembly to meet the required 90 Deg intent especially with continuous load nature of EVSE.

Yes limited to 60° C for ampacity but the conductors are clearly 90° C. Even MC cable or conduit and wire with 90° C condcutors is still limited to 75° C by the terminations so then you couldn't use that either. I see no issue if equipment requires 90° C conductors using NM cable because the conductors are 90° C.

334.112 Insulation.
The insulated power conductors shall be one of the types listed in Table 310.4(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).
Informational Note: Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this requirement.

 

[paullmullen]

Short correction to @infinity for those trying to follow the thread... T310.4(A) should be T310.104(A)


Question for @infinity... 334.112 talks about the construction of the NM-family of cables. It's not about the application of them, right?


@Fred B , you read it the same way I read it. I think the way the instructor installed - assuming he was not making an error - was to use SE cable following 338.10(B)(4) including the exclusion of temperature limitations in 334.80.

 

[electrofelon]

I thought some fused disconnects were 90°

Maybe I am incorrect, but I thought it was pretty much a universal thing for low voltage equipment. If you feel like doing some digging and finding an example, I would like to see it

 

[infinity]

Question for @infinity... 334.112 talks about the construction of the NM-family of cables. It's not about the application of them, right?

Yes the cable is required to be constructed with 90° C conductors. If a piece of equipment says that it requires 90° C conductors since NM cable has 90° C conductors it would be permitted to be used.

 

[LarryFine]

I've had multiple EVSE that required 90 deg wire and copper only (printed inside of equipment and manual), that eliminates NM and AL-SER as a wiring option.

Only at the terminals, not the entire circuit.

 

[letgomywago]

Maybe I am incorrect, but I thought it was pretty much a universal thing for low voltage equipment. If you feel like doing some digging and finding an example, I would like to see it

I'll take a look I've got a few

 

[electrofelon]

I'll take a look I've got a few

This is from an IAEA article. I would have liked a reference to some standard, but they do not provide that.

2. Conductors with higher than 75°C ratings, provided the conductor ampacity does not exceed the 75°C ampacity of the conductor size used (see figure 8). This condition also permits the conductors to be used at ampacities higher than 75°C if the equipment is listed and identified for the higher rating. However, for equipment rated 600V and lower, there is no listed equipment with termination ratings above 75°C.

 

[letgomywago]

This is from an IAEA article. I would have liked a reference to some standard, but they do not provide that.

Makes me want to check into this. If there is as ive been told then that's a big blunder. I'm sure they're right but I've seen and heard things from incorrect sources. I've seen people make claims about nm connectors before that don't match ul listing.