Wire Guage clarification help.

[dradam]

A licensed Electrician will be helping me to install my EVSE about a 35 foot run from the subpanel in my garage. He wants to use 6AWG romex on a 60 amp breaker for what will be, I hope, charging if needed at 48A.

Been reviewing the forms here and still the safest option is not clear to me. 6AWG romex is rated at 55 amps. Some say you must use a wire that is rated for 60A for a 60A breaker. Some say the charger will never pull more than 48A so it is safe.

6 AWG THHN appears to to be rated at 65 Ampacity but my electrician says that 6AWG will actually run hotter in a conduit even of appropriate diameter. I had thought the opposite.

I can easly run a cable or conduit.

Any advice would be appreciated.

Go with 6AWG romex ?
Go with 4AWG romex 70 ampacity (many say it fits in the charger connector) ?
Go with conduit ?

TIA

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[NY_Rob]

You can't run 6 AWG Romex (NM-B in the chart below) which is rated for 55amps off a 60amp breaker, as the breaker can't have a higher trip rating than the circuit wire max capacity for obvious reasons (think of a short circuit which would allow 60amps to run through the 55amp rated wire).

4 AWG Romex would probably be easier to run then installing conduit and pulling 3 or 4 THHN cables through it depending on how many twists and turns it makes.

It's a little concerning that the electrician was willing to install a 60 amp breaker on 55amp rated cable because "it will not exceed 48 amp load".. well accidents happen and that's why we use breakers in the first place. Secondly, a 55 amp rated 6 AWG Romex cable needs to be derated by 20% under "continuous load" (which is how our EVSE's are classified) so that would be 44 amps max load, not 48 amps on that 6 AWG Romex.

 

[dradam]

Thank you Rob,

I agree with your thinking. It is my understanding that 4AWG will fit in the charger . Have you heard this as well? I agree it would be much easier for me to run 4AWG romex than conduit.

I appreciate your help.

 

[cjust2006]

4AWG to be 100% safe. I have 6AWG on a 60A breaker, but I cap my charger at 40A just for a good overhead. I only go to 48A when in a pinch. It's completely DOABLE. The wire will run warmer, but if you're using THHN, then max temp is 194F, which occurs around 75A. At 48A, you'll be around 116F-118F. Hot water temperatures... Regardless, even to reach the temperature threshold of 6AWG THHN wire, you'd have to surpass the amperage of the breaker.

If I'm not mistaken, it's even permitted by code for that reason. Correct me if I'm wrong.

Again, NOT IDEAL. Don't shoot! I get it. That's why I dial it down to 40A. Do I think anything would happen at 48A? No.

 

[godfodder0901]

Thank you Rob,

I agree with your thinking. It is my understanding that 4AWG will fit in the charger . Have you heard this as well? I agree it would be much easier for me to run 4AWG romex than conduit.

I appreciate your help.

I used 6AWG THHN. I think 4 is too big, plus it's harder to manipulate. Don't use any Romex.

 

[dradam]

Thank you Jared,
Why no romex even if it exceeds the ratings?

 

[DuoRivians]

Don’t use romex. Runs too hot. Use 6 AWG THHN

 

[godfodder0901]

Thank you Jared,
Why no romex even if it exceeds the ratings?

Just easier to manage a 6 AWG wire, and 6 AWG at 60 amps can't be done with NM-B.

 

[jjswan33]

Thank you Jared,
Why no romex even if it exceeds the ratings?

You can use 6awg Romex but you have to keep it to a max 50A circuit which means charging at 40A. Honestly it's what I have (Romex 6-3, 50A circuit, Nema 14-50 Outlet and a Chargepoint HomeFlex) but I had Romex left over from installing my Hot Tub so it was free.

 

[dradam]

Thanks to all.
So if I don't use 4AWG romex because it is too hard to handle and use 6AWG THHN in conduit (6/3 and a ground for future proofing) instead, (which is OK for a 60 A Breaker) , Can I use a flex conduit ? If so I think 1 inch would be OK. My electrician was against conduit and THHN-- said it would be hotter? Is he mistaken?

TIA

 

[Dark-Fx]

You can use 6awg Romex but you have to keep it to a max 50A circuit which means charging at 40A. Honestly it's what I have (Romex 6-3, 50A circuit, Nema 14-50 Outlet and a Chargepoint HomeFlex) but I had Romex left over from installing my Hot Tub so it was free.

You can breaker a 6 AWG Romex at 60A but you can't exceed the 80% rule of the wire ampacity. Rivian's charger doesn't support setting to 55*.80 (44A), but some do.

Either way, I wouldn't recommend doing it this way because it confuses some inspectors.

 

[DuoRivians]

Thanks to all.
So if I don't use 4AWG romex because it is too hard to handle and use 6AWG THHN in conduit (6/3 and a ground for future proofing) instead, (which is OK for a 60 A Breaker) , Can I use a flex conduit ? If so I think 1 inch would be OK. My electrician was against conduit and THHN-- said it would be hotter? Is he mistaken?

TIA

Yes for 60a breaker, yes for 1” conduit. But not sure about flex. I used pre-bent conduits

 

[SparkyR1t]

Remember team the NEC is the minimum standard for safety to prevent fires

So regardless of what you have the vehicle set for for amperage the electrical supply system must meet NEC standards or better. Also when you install systems you may have a plan to use substandard wiring knowing you will back down the charging current of the vehicle to be safe but the installed system must be 100% usable for the next guy who may and should be able per the installed breaker and wiring max out the vehicle charging current since he/she will assume the install was per code

 

[SANZC02]

Thanks to all.
So if I don't use 4AWG romex because it is too hard to handle and use 6AWG THHN in conduit (6/3 and a ground for future proofing) instead, (which is OK for a 60 A Breaker) , Can I use a flex conduit ? If so I think 1 inch would be OK. My electrician was against conduit and THHN-- said it would be hotter? Is he mistaken?

TIA

6 awg thhn in 3/4 conduit is good for 75 amps. Honestly I would probably get a quote from another electrician and make sure he is getting permits for the work.

The electrician has given you 2 pieces of information that would cause me to not trust their knowledge or work.

 

[NY_Rob]

My electrician was against conduit and THHN-- said it would be hotter? Is he mistaken?

Well, NM-B (Romex brand in this case) is directly air cooled, so it "might" run slightly cooler then THHN inside a sealed conduit, but THHN is Rated for 194F, so no worries there.

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