4 AWG or 6 AWG copper wire for 60A 2pole breaker?

[tmeyer3]

Sorry I need to add my 2 cents lol. We almost always want to install devices per the manufacturers installation instructions. The National Electrical Code (NEC) even has a section for this, NEC 110.3B.
You have taken into consideration the length of the run, so no need for a voltage drop calculation.
The other thing that most are not aware of is something the NEC defines as a continuous load. If the load on a branch circuit is continuous for 3Hrs or more, it must be derated to 80%. If my math is correct... the max (continuous) 48amps of the charger is 80% of a 60amp branch circuit (or you can do the inverse and multiply 48amps by 125%). I believe that is NEC 210.23b?
You should also consider the size limitations of the lugs you will land the wires on. Some lugs will require solid conductors.
I hope I haven't confused the issue more lol. Hey, my fellow EC's, let me know if I missed anything.

This is correct. It is right on the border there at 48a (charger) 10' run. Though iirc (please correct if wrong) the NEC states that 6AWG is ok continuous at 65a * .8 = 52a. So you're good to go with 6AWG copper on a 60a breaker with a 48a continuous load!

Good luck on your project!

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[HaulingAss]

Thanks Wade. I agree. 4 awg is best for a 60A breaker as this is considered continuous duty. I will use MC 4/3 will cap the neutral for future NEMA 14-50.

Not all electrical wire has the same allowable continuous amperage ratings for the same gauge. The Electrical Code covers this in detail. @mongo provided the correct answer. When using THHN/THWN in conduit, 6AWG is more than good for a short run. You could debate at what length of run it starts making sense to use 4 AWG, but a 10-foot run is nowhere near that threshold.

Yes, if you use Romex, 4 AWG.

Again, focus on the quality of the equipment the wire is attached to, and the quality of the workmanship used to connect it, not boosting the size of the wire without good cause.

 

[mongo]

This is correct. It is right on the border there at 48a (charger) 10' run. Though iirc (please correct if wrong) the NEC states that 6AWG is ok continuous at 65a * .8 = 52a. So you're good to go with 6AWG copper on a 60a breaker with a 48a continuous load!

Good luck on your project!

Agreed, I wouldn't call it "right on the border" though. A breaker and wire with 60A ampacity both get derated 80% and so are fine with a 48A continuous load. Bumping up the gauge for a 10 foot run has practically no benefit.

Regarding voltage drop:
If planning for 3% drop on a branch circuit (NEC recommend maximum) at 48A and 240V:
240*3%=7.2V
7.2V/48A = 0.15 Ohm total
If connections are ideal (which they aren't)
0.15 Ohm / 2 = .075 Ohm each conductor (roundctrip)
6 AWG; 0.403 Ohm/1000 ft
.075/(0.403/1000ft)=186 feet max run

Going up to 4 AWG (on the same run)
4 AWG: 0.253 Ohm/1000 ft
186 ft * (0.253/1000) = 0.0471 Ohm (per conductor)
*2 = 0.094 Ohm round trip
*48A = 4.52V
/240 = 1.9% voltage drop

Power loss:
6 AWG: 7.2V * 48 A = 346 W
4 AWG: 4.52V * 48 A = 217 W
Difference: 129W
If electricity costs $0.20/ kWh then every 10 hours of charging saves $0.26
Or, say you drive 12,000 miles per year and average 400 Wh/mile and charging is 95% efficient, that's roughly
12,000 * .4 / 0.95 =5,053 kWh/yr, call it 5 MWh
Branch loss:
6 AWG: 5MWh*3% = 150 kWh
4 AWG: 5MWh*1.9% = 95 kWh
Savings: 55 kWh * $0.20 = $11/yr

Wire costs:
186*2=372 feet
6 AWG: 0.92/ft * 372 = $342
4 AWG: $1.41/ft * 372 = $525
Plus, ground needs upsided also (but let's ignore that)
$183 cost increase
/$11= 16.6 year (200,000 mile) break even.

For 10 foot run, 20 ft round trip
6 AWG: $18.40
8.06 mOhm, 387mV drop, 18.6 W loss
4 AWG: $28.20
5.06 mOhm, 243 mV drop, 11.7 W loss
6.9 W improvement, $9.80 cost increase (ignoring ground)
$9.80 / $0.20 = 49 kWh for breakeven
/.0069 = 7,100 hours of charging to break even
= 82 MWh
= the same 17 year payback (at 12k miles a year 400 Wh/mile 100% efficiency)

 

[AlmostHuman]

Agreed, I wouldn't call it "right on the border" though. A breaker and wire with 60A ampacity both get derated 80% and so are fine with a 48A continuous load. Bumping up the gauge for a 10 foot run has practically no benefit.

Regarding voltage drop:
If planning for 3% drop on a branch circuit (NEC recommend maximum) at 48A and 240V:
240*3%=7.2V
7.2V/48A = 0.15 Ohm total
If connections are ideal (which they aren't)
0.15 Ohm / 2 = .075 Ohm each conductor (roundctrip)
6 AWG; 0.403 Ohm/1000 ft
.075/(0.403/1000ft)=186 feet max run

Going up to 4 AWG (on the same run)
4 AWG: 0.253 Ohm/1000 ft
186 ft * (0.253/1000) = 0.0471 Ohm (per conductor)
*2 = 0.094 Ohm round trip
*48A = 4.52V
/240 = 1.9% voltage drop

Power loss:
6 AWG: 7.2V * 48 A = 346 W
4 AWG: 4.52V * 48 A = 217 W
Difference: 129W
If electricity costs $0.20/ kWh then every 10 hours of charging saves $0.26
Or, say you drive 12,000 miles per year and average 400 Wh/mile and charging is 95% efficient, that's roughly
12,000 * .4 / 0.95 =5,053 kWh/yr, call it 5 MWh
Branch loss:
6 AWG: 5MWh*3% = 150 kWh
4 AWG: 5MWh*1.9% = 95 kWh
Savings: 55 kWh * $0.20 = $11/yr

Wire costs:
186*2=372 feet
6 AWG: 0.92/ft * 372 = $342
4 AWG: $1.41/ft * 372 = $525
Plus, ground needs upsided also (but let's ignore that)
$183 cost increase
/$11= 16.6 year (200,000 mile) break even.

For 10 foot run, 20 ft round trip
6 AWG: $18.40
8.06 mOhm, 387mV drop, 18.6 W loss
4 AWG: $28.20
5.06 mOhm, 243 mV drop, 11.7 W loss
6.9 W improvement, $9.80 cost increase (ignoring ground)
$9.80 / $0.20 = 49 kWh for breakeven
/.0069 = 7,100 hours of charging to break even
= 82 MWh
= the same 17 year payback (at 12k miles a year 400 Wh/mile 100% efficiency)

I agree, for that short of a run it likely doesn't matter. I have a hard time not bumping up the gauge when doing wiring like this I'd still recommend doing the 3 wire with a ground to give you more options in the future.

 

[Vuong785]

I agree, for that short of a run it likely doesn't matter. I have a had time no bumping up the gauge when doing wiring like this I'd still recommend doing the 3 wire with a ground to give you more options in the future.

Excellent advices and thanks for the calculations from Mongo.

 

[TruckGenio]

Should I use 6AWG conductors for a 10’ run for the direct wired 60A breaker?

6AWG is acceptable 4 AWG is preferable the further you’re gonna go the better off you are with a 4AWG.

 

[mongo]

For long runs, aluminum transitioning to copper before the wall connector (like at a subpanel) can be less loss and cost.

 

[HaulingAss]

I agree, for that short of a run it likely doesn't matter. I have a hard time not bumping up the gauge when doing wiring like this I'd still recommend doing the 3 wire with a ground to give you more options in the future.

It makes zero sense to put an unused copper conductor inside the conduit. Install the wires you need, not ones you imagine you might want for some unknown reason in the future. I've already made that mistake 7 years ago and that big copper wire is still there, completely unused. It will NEVER be used, it was a waste of time and money (and resources). Hopefully the copper is recycled when the structure is at its end of life in 50-75 years.

Sure, you can always dream up "what-ifs", my point is they are very unlikely to materialize. It's better to only install the wiring you need today unless you have in mind a specific future upgrade that is actually likely to materialize. Converting a Wall Connector to a NEMA 14-50 is not one of them. For anyone. All home charging units I'm familiar with only need two conductors and a ground. All adding an unused wire does is increase sales of copper wire.

 

[HaulingAss]

For long runs, aluminum transitioning to copper before the wall connector (like at a subpanel) can be less loss and cost.

Of course. But if designing the circuit from scratch it normally doesn't make sense to have any connections between the breaker and the Wall Connector. It could make sense for a power feed to a distant outbuilding, not for a normal run from a service panel to a Wall Connector within a house.

 

[AlmostHuman]

It makes zero sense to put an unused copper conductor inside the conduit. Install the wires you need, not ones you imagine you might want for some unknown reason in the future. I've already made that mistake 7 years ago and that big copper wire is still there, completely unused. It will NEVER be used, it was a waste of time and money (and resources). Hopefully the copper is recycled when the structure is at its end of life in 50-75 years.

Sure, you can always dream up "what-ifs", my point is they are very unlikely to materialize. It's better to only install the wiring you need today unless you have in mind a specific future upgrade that is actually likely to materialize. Converting a Wall Connector to a NEMA 14-50 is not one of them. For anyone. All home charging units I'm familiar with only need two conductors and a ground. All adding an unused wire does is increase sales of copper wire.

It is not in conduit, it is all in the wall and would be basically impossible to do it how I ran it after some things are finished in the basement and other areas of the house. I was willing to pay the extra money to have the knowledge that I could change it to a NEMA 14-50 or anything that needs 3 wire and ground. Same as wiring the home with CAT 7A. Am I using 10GbE everywhere in the house right now, nope. It will be nice in the future when I want to have something connected at 10GbE to the main house switch

You can't say that converting a Wall Connector to something else is not something anyone may want to do, who knows what the future holds!

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