Wiring for Level 2 Charger

[Joey D]

I have seen conflicting information on this...anyone know for sure?

When wiring a level 2 charger for home (yeah...yeah...it's technically a "EVSE"), I am planning on supporting the following:

* 48 Amp Charge Rate (to fully support max charge rate of Model S)
* All indoor wiring (basement to attached garage)

I understand that
1) 60 Amp circuit is needed to support 48 amp continuous load
2) This needs to be direct wired. (No receptacles)

Where I am not sure...is on the wire type requirements. Normally 6-2 Romex wire would be sufficient for a 60 Amp circuit. However, I have read along the lines of this not being up to code for this application? That for a 60 Amp circuit, (even though the draw will be 48 amps?) that either 4-2 Nomex, or THHN in conduit is generally required to be up to code?

Can anyone definitively answer?

 

[Big Earl]

You need one of the following:

• 4/2 Romex
• 6 gauge THHN in conduit
• 6/2 MC armored cable, which is the equivalent of THHN in conduit without having to deal with conduit

I went with MC cable and am very happy with the result.

 

[DerbyDave]

Yeah, 6 guage Romex is not enough, as Big Earl says. You need 4 guage Romex. We got a bunch of people on here that know this stuff, and I made the mistake of letting my professional use 6 guage Romex. I am generally limiting my charging to 40A, except occasionally.

 

[Joey D]

Thanks for the input.

My professional is also telling me : "6-2 romex is fine....do it all the time." I'm sure he does, and I'm sure it will cost incrementally more for the other wire options...but at least it will be done right.

So I'll either chose to limit the circuit to 50 Amp breaker (and limit myself to 40 Amp charging) and use 6-2 Romex, or go for the full 60 Amp Breaker but insist on 4/2 Romex, 6/2 TTHN in conduit or 6/2 MC.

 

[Cosmacelf]

The only conflicting information comes from "professionals". The electrical code is very clear. 6/2 Romex cannot be used for any 60A breaker circuit. Personally, I like using 6/2 MC cable. More info: CarCharging.us

 

[aerodyne]

And, a good primer here:

Home Charging Wiring Guide – TeslaTap

teslatap.com

Personally, I rarely have a need to go beyond 31A.

 

[ucmndd]

Normally 6-2 Romex wire would be sufficient for a 60 Amp circuit.

6/2 NM-B (Romex) cable is _never_ sufficient for a circuit drawing 48 continuous amps according to the NEC.

Yes, it works. Yes, people - even electricians - do it “all the time” with no negative effects. But the code is clear as can be.

 

[mswlogo]

6-2 Romex is really 55 Amps. But they don’t make a 55 Amp breaker. Code allows use of a 60 Amp breaker. But it’s still a 55 Amp circuit and not enough for a 48 Amp continuous load.

 

[Cosmacelf]

6-2 Romex is really 55 Amps. But they don’t make a 55 Amp breaker. Code allows use of a 60 Amp breaker. But it’s still a 55 Amp circuit and not enough for a 48 Amp continuous load.

Code does not allow use of a 60A breaker.

 

[ucmndd]

Code does not allow use of a 60A breaker.

I think technically it would if your calculated load for the circuit was less than 55 amps (or 80% of 55 amps for continuous loads, i.e. 44 amps) via the round-up rule.

But the calculated load of an EVSE providing 48 amps continuously is clearly greater than 44 amps, so it’s a no-go.

A hypothetical 44 amp EVSE, on a 60 amp breaker with 6/2 romex, should be fine.

 

[mswlogo]

Code does not allow use of a 60A breaker.

Yes it does.

2023 Code Language:

240.4(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.

(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).

(3) The next higher standard rating selected does not exceed 800 amperes.

If the overcurrent protective device is an adjustable trip device installed in accordance with 240.4(B)(1), (B)(2), and (B)(3), it shall be permitted to be set to a value that does not exceed the next higher standard value above the ampacity of the conductors being protected as shown in Table 240.6(A) where restricted access in accordance with 240.6(C) is provided.

 

[MN-MS100D]

Yes it does.

2023 Code Language:

240.4(B) Overcurrent Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:

(1) The conductors being protected are not part of a branch circuit supplying more than one receptacle for cord-and-plug-connected portable loads.

(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).

(3) The next higher standard rating selected does not exceed 800 amperes.

If the overcurrent protective device is an adjustable trip device installed in accordance with 240.4(B)(1), (B)(2), and (B)(3), it shall be permitted to be set to a value that does not exceed the next higher standard value above the ampacity of the conductors being protected as shown in Table 240.6(A) where restricted access in accordance with 240.6(C) is provided.

Does not apply in this case. Common mistake made by internet searchers and electricians, too.

Article 625.41 states that the overcurrent protection must be sized for continuous duty. Article 90 describes how Code Chapters 1-4 can be supplemented by additional requirements in Chapters 5-7, which is the case here, so next upsize rule in 240.4B cannot be used for EVSE's.

Clear as mud.

 

[mswlogo]

Does not apply in this case.

Exactly what I said and was my point why it’s confusing.

Actually, if I’m not mistaken a 60 Amp breaker is allowed here. But it remains a 55 Amp rated circuit. You could load it with 80% of 55 Amps (i.e. 44 Amps continuous). But there is no hard setting on the Wall Connector or Mobile connector for 44 Amps. So you need to round down to 40 Amps. If you do that you might as well put a 50 Amp breaker.

They give you wiggle room on OVERLOAD PROTECTION (i.e. a short) it does not change actual load which is based on the wire specs.

You can improperly load any circuit and be below breaker rating.

 

[Rocky_H]

Normally 6-2 Romex wire would be sufficient for a 60 Amp circuit.

You state that as if it is a given fact as the premise before asking your question, but this is never true. Never ever. That 6 gauge Romex only has a 55A rating, so it cannot be used for a 60A circuit.

And then we devolved into the weeds on the "round up rule". @mswlogo and @ucmndd have this correct with all of the messy details and caveats.

A continuous duty device if it were operating at 44A would need 125% oversize of that as a 55A circuit. That would then technically be allowed to use a rounded up 60A breaker, BUT IT'S NOT A 60A CIRCUIT! At a 48A setting? No, you can't.

So then the practical reality is that you just don't find any charging devices that have a 44A setting, so this round up rule technicality can almost never be used. The only people who try to use it are usually getting it wrong, so we generally just discourage bringing it up. If you're using wire that only has a 55A rating, just make it a 50A circuit and stop trying to find a loophole.

 

[Joey D]

You state that as if it is a given fact as the premise before asking your question, but this is never true. Never ever. That 6 gauge Romex only has a 55A rating, so it cannot be used for a 60A circuit.

Duly noted...yes I understand what you're saying and I should not have stated it that way.

 

[Rocky_H]

Duly noted...yes I understand what you're saying and I should not have stated it that way.

I'm sorry for sounding so strong on that. I just see this same mistake often (twice more today), and I was letting the frustration get to me.

 

[aerodyne]

Good discussion. I should add for those that come after, that a GFCI breaker should be used for an outlet in a garage or wet location.

50 amp breaker, 3 foot run of 6 Ga, and a 6-50 outlet work for me, limited by MC at 31A but still 28 miles an hour.

 

[DerbyDave]

Good discussion. I should add for those that come after, that a GFCI breaker should be used for an outlet in a garage or wet location.

50 amp breaker, 3 foot run of 6 Ga, and a 6-50 outlet work for me, limited by MC at 31A but still 28 miles an hour.

The Tesla Gen 3 Wall Connector says not to use an additional GFCI since the Wall Connector already has one:
"Ground Fault Circuit Interrupter Integrated, no additional required (CCID20)"

 

[aerodyne]

The Tesla Gen 3 Wall Connector says not to use an additional GFCI since the Wall Connector already has one:
"Ground Fault Circuit Interrupter Integrated, no additional required (CCID20)"

Good point. I did say outlet, but should have been more clear.

 

[Joey D]

I'm sorry for sounding so strong on that. I just see this same mistake often (twice more today), and I was letting the frustration get to me.

No worries, mate!