Wire Gauge Size for 50 Amps

[MD-2000]

>At 40 A over a wire run of 5 m for 9 hours, total energy lost over the wire run for a 300-mile full charge is:
>for AWG#6: (40 A)^2 x (5 m x 1.296 mΩ/m) x 9 hr = 0.093 kWh
>for AWG#5: (40 A)^2 x (5 m x 1.028 mΩ/m) x 9 hr = 0.074 kWh
>for AWG#4: (40 A)^2 x (5 m x 0.8125 mΩ/m) x 9 hr = 0.059 kWh

I do have to wonder - 0.093kWh would cost me 8/10 cent or maybe 25 cents a month. The problem then is only the heat issue.

I was told code was 40A/8Ga and 50A/6Ga, that is 40A breaker and 50A breaker. *Then* you figure that code also says never draw continuously for extended periods more than 80% of max Amperage - so 32A or 40A respectively. I have a 50A circuit and my Wall Charger (gen2) is set to 40A max.

Considering the possible outcomes, why bother pushing the limits? If you have 8Ga, limit your charging to 32A/240V. If you schedule charging for 1AM, odds are you will be fully charged in the morning or the morning after, unless you consistently go very long distances - if you do that, spend the money for a thicker cable.

By the way, I use this:
General Electric WX09X10037 4-Feet 50-Amp 4 Wire Range Cord
https://www.amazon.ca/gp/product/B00LQDFOMY

I have this connected to my wall charger, so I can keep my 14-50 socket in the garage. This works well, this cable never even gets warm to the touch. BTW, the charger only uses ground, red and black, the white is capped off. Interestingly in this product, ground and white is 8Ga and red and black are 6Ga.

 

[AreV]

So I can have my electrician pull 6 AWG, and leave the breakers? I paid a licensed electrician and pulled permits and it was inspected and passed! O well.

 

[Rocky_H]

So I can have my electrician pull 6 AWG, and leave the breakers? I paid a licensed electrician and pulled permits and it was inspected and passed! O well.

Pulling the wire is usually the expensive part in terms of labor cost because it takes the most time. Since you are using an outlet, you are using the mobile charging cable that comes with the car, right? That cable pulls a maximum of 32A, which is the appropriate amount for a 40A circuit. And since there is no outlet type specifically for 40A, electric code does allow the exception of putting 50A outlet types on 40A rated circuits. This is very often done for ovens.

So trying to re-pull larger wire to make it a real 50A circuit won't gain you any more power or charging speed anyway. I would say just swap the breaker to a 40A to get code compliant and leave the 8 gauge Romex, and it's fine. That will certainly be cheaper on labor time--should just take a few minutes. And you might be able to negotiate for a cheap/free visit to get the electrician to do that few minutes to fix it by pointing out that his original choice of 8 gauge Romex on a 50A breaker violates code, so this should be corrected.

 

[hcdavis3]

Pulling the wire is usually the expensive part in terms of labor cost because it takes the most time. Since you are using an outlet, you are using the mobile charging cable that comes with the car, right? That cable pulls a maximum of 32A, which is the appropriate amount for a 40A circuit. And since there is no outlet type specifically for 40A, electric code does allow the exception of putting 50A outlet types on 40A rated circuits. This is very often done for ovens.

So trying to re-pull larger wire to make it a real 50A circuit won't gain you any more power or charging speed anyway. I would say just swap the breaker to a 40A to get code compliant and leave the 8 gauge Romex, and it's fine. That will certainly be cheaper on labor time--should just take a few minutes. And you might be able to negotiate for a cheap/free visit to get the electrician to do that few minutes to fix it by pointing out that his original choice of 8 gauge Romex on a 50A breaker violates code, so this should be corrected.

There is nobody more knowledgeable on this forum than Rocky. He is to be trusted implicitly.

 

[Rocky_H]

Jeez, man. It's just people asking the same kinds of questions every week for several years, so I get to practice these answers a lot.

 

[AreV]

Thanks all. Rocky, I've already decided to change the breakers. Same line of thinking. I can't have the electrician back as he moved to Florida. The inspector that passed it is a county employee and no joy would be had there. It is only a part of rewiring three existing circuits and adding a new outlet circuit and switch over a tool area. It is all exposed now as the Garage was never finished out inside. So I am pulling new Romex in walls, then insulate and sheet-rock/prep and paint the walls.

I was told that the Tesla charger head would charge much faster and I wonder if I am wrong in thinking that it doesn't based on hearsay at Tesla while buying my MY.

 

[Rocky_H]

I was told that the Tesla charger head would charge much faster and I wonder if I am wrong in thinking that it doesn't based on hearsay at Tesla while buying my MY.

Ha ha ha! Who said that? I'm wondering if this is another thing that needs to be added to the file of dumb/wrong things Tesla salespeople have said.
No, the brand or type of home charging unit can't make any difference in charging speed. That's because it's not processing or really doing anything except closing a switch to make a connection. You have the wires of the circuit in your wall, and they are separated from the car until that device determines that it's safe to then complete the circuit to pass those "wires" into your car, and the charger there inside the car does the real work of converting it from 240V alternating current to about 400V direct current, which is applied to charge the battery.

As long as you're not artificially limited by a max capability at any of these three places, you'll get the same charging speed from every kind of connector for AC type of charging.
1. Your circuit can provide XX number of amps.
2. Your connector can pass through that same XX number of amps.
3. Your car's internal charger can process that same XX number of amps.

It's a matter of the lowest common denominator among those three capabilities that will determine what it's capable of.

 

[AreV]

Thanks Rocky. As I said I thought at the time it was sales BS nothing more. Or I would have bought one. My wife and I are retired contractors who subbed out the electrical installations.

I swapped out the 100 Amp service for 200Amp service just to be safe as we had an electric range and electric dryer. Electric gas furnace and fireplace vented outside. With the right (or wrong) set of circumstances could brown out and damage electronics inside. We changed all the kitchen appliances and I had a gas line and gas range installed. The garage is the last part we are updating.

 

[ka9q]

Anybody know how the 14-50 outlet became the standard for Tesla charging? The 14-50 has a neutral blade that EV chargers (HPWC or J1772) don't need, but I strongly suspect the NEC requires that the 14-50 be wired with a neutral. (If it doesn't, it should. Plugging a different load that does require a neutral into a 14-50 without one could be dangerous.) So meeting code with a 14-50 means paying for a neutral wire you won't need.

The NEMA 6-50 is designed for 250V-only 50A loads that don't need a neutral. It's often used for welding equipment. Seems like it should be the EV standard.

I know that the 14-50 is very common in RV parks for larger RVs with big HVAC systems, but that's not a reason to standardize on it for home EV charging. Tesla's portable charger is available with both 14-50 and 6-50 plugs; I carry both.

 

[swaltner]

The 14-50 became the “standard” for EV charging because it was the only thing available for “fast” (well, not excruciatingly slow) charging before DC Fast Chargers became widely available. 12 years ago in the days of the original Tesla Roadster, the only public outlets with any power were 14-50 outlets that were installed at RV campgrounds. These were 14-50 outlets because RVs needed the 120v option that this outlet provides. People that wanted to do long distance travel in a Roadster jumped from campground to campground.along the way. You could recharge at public EV charging stations, but these all tended to be ones at 30 amps, making long charging stops even longer.

Edit: Before plugshare, EV travelers found their charging stops using the KOA web site or other on-line lists of RV campgrounds.

 

[TampaBruce]

Thinking of going 6-50. Wire would be 6/2, much cheaper than 6/3 and easier to work. Since many of the 'off' brand chargers utilize a NEMA 6-50 plug I wonder why most folks in this thread seem to be going to 14-50 configuration. The Tesla Home Charger (Gen 2) is a 3 wire device (2 conductors and a ground) so seems the most economical way to go would be 6/2 hard wired.
Ex-electrician - just looking for some feedback.

 

[miimura]

Thinking of going 6-50. Wire would be 6/2, much cheaper than 6/3 and easier to work. Since many of the 'off' brand chargers utilize a NEMA 6-50 plug I wonder why most folks in this thread seem to be going to 14-50 configuration. The Tesla Home Charger (Gen 2) is a 3 wire device (2 conductors and a ground) so seems the most economical way to go would be 6/2 hard wired.
Ex-electrician - just looking for some feedback.

Your logic is sound. Go ahead with your plan to wire a 6-50 outlet. The Mobile Connector supplied with the car no longer includes a 240V adapter, just a NEMA 5-15 120V adapter, so if you're going to buy one, you might as well buy the 6-50 adapter instead of the 14-50 adapter.

In my garage, I have one of each. My 2018 Model 3 came with a 14-50 adapter so that car uses a 14-50 on that side of the garage. My Leviton 40A EVSE has a 6-50 plug so I changed the outlet on that side of the garage to 6-50. The Neutral wire is capped with a wire nut behind the outlet.

 

[5thBMouse]

Hello everyone, not to beat a dead horse here but I moved into a house with a 50 amp circuit with #8 THHN/THWN wire in conduit that runs to a box in the garage. The box that it runs to has 2 shut-off switches (one for a heater and one for a pump to a hot tub that no longer exists.) I am thinking of replacing the box with the 2 shut-offs with a surface mounted NEMA 14-50 recepticle at the end of the conduit. The charger that I intend on getting is rated at 40 amps (juicebox 40) and the car I will be charging i believe caps out at 28 amps (not a Tesla). Any major red flags with this plan?

 

[nwdiver]

Hello everyone, not to beat a dead horse here but I moved into a house with a 50 amp circuit with #8 THHN/THWN wire in conduit that runs to a box in the garage. The box that it runs to has 2 shut-off switches (one for a heater and one for a pump to a hot tub that no longer exists.) I am thinking of replacing the box with the 2 shut-offs with a surface mounted NEMA 14-50 recepticle at the end of the conduit. The charger that I intend on getting is rated at 40 amps (juicebox 40) and the car I will be charging i believe caps out at 28 amps (not a Tesla). Any major red flags with this plan?

Just use a 40A breaker...

 

[5thBMouse]

Just use a 40A breaker...

Awesome, thanks for such a quick response! Just a quick follow up question. My understanding is that I would need to use a 50 amp breaker due to the '80% rule'? If the charger is pulling a max of 40 amps, it's that not the case?

 

[nwdiver]

Awesome, thanks for such a quick response! Just a quick follow up question. My understanding is that I would need to use a 50 amp breaker due to the '80% rule'? If the charger is pulling a max of 40 amps, it's that not the case?

If you pull 40A the breaker will probably trip. But you should only be pulling 28A... correct? 80% is just the continuous load the breaker can support without 'nuisance tripping'.

 

[miimura]

Hello everyone, not to beat a dead horse here but I moved into a house with a 50 amp circuit with #8 THHN/THWN wire in conduit that runs to a box in the garage. The box that it runs to has 2 shut-off switches (one for a heater and one for a pump to a hot tub that no longer exists.) I am thinking of replacing the box with the 2 shut-offs with a surface mounted NEMA 14-50 recepticle at the end of the conduit. The charger that I intend on getting is rated at 40 amps (juicebox 40) and the car I will be charging i believe caps out at 28 amps (not a Tesla). Any major red flags with this plan?

As long as you only use that circuit for charging and don't connect any of the previous loads, you will be fine with the existing 50A breaker and installing a 14-50 receptacle. The 14-50 must be the only thing connected to the circuit. #8 THHN in conduit is up to code for 50A. The #8 NM-B wire discussed earlier in this thread is not. The 40A EVSE on a 50A circuit is exactly correct. Don't use a 40A breaker. @nwdiver usually knows what he's talking about but his posts above don't make sense to me.

 

[nwdiver]

As long as you only use that circuit for charging and don't connect any of the previous loads, you will be fine with the existing 50A breaker and installing a 14-50 receptacle. The 14-50 must be the only thing connected to the circuit. #8 THHN in conduit is up to code for 50A. The #8 NM-B wire discussed earlier in this thread is not. The 40A EVSE on a 50A circuit is exactly correct. Don't use a 40A breaker. @nwdiver usually knows what he's talking about but his posts above don't make sense to me.

Might be ok... it depends on how much you have to derate the wire based on ambient temperature. But I've never seen #8 THHN used on a 50A circuit. Using a 40A breaker especially if you don't expect to pull >30A seemed the safer course.

 

[Rocky_H]

The charger that I intend on getting is rated at 40 amps (juicebox 40)

Just clarify what you mean by "rated at". It's confusing if people don't specify which thing they are talking about with EVSE units, because they will sometimes list a number of amps for either of these two specifications:
1. What size circuit it is supposed to use
or
2. How much continuous current it will supply.
The answers obviously will be different depending on which of those two things the "40A" is referring to. I just looked up the Juicebox 40, and it supplies 40A and says to use a 50A circuit, so that is clear.

I moved into a house with a 50 amp circuit with #8 THHN/THWN wire in conduit that runs to a box in the garage. The box that it runs to has 2 shut-off switches (one for a heater and one for a pump to a hot tub that no longer exists.) I am thinking of replacing the box with the 2 shut-offs with a surface mounted NEMA 14-50 recepticle at the end of the conduit.

Yes, that is normal enough and code compliant. 8 gauge in conduit is rated fine for 50A circuits. The Juicebox 40 wants a 14-50 outlet type to plug into, and that circuit will support it if you do have all four wires there available: two hots, neutral, and ground. Please get some other brand of outlet than Leviton, though.