Pluturi
Member
I’m all for having the outlet wired correctly, but help me understand the benefit of replacing the 6-50 with a 14-50. Compatibility for his UMC when traveling? Otherwise I don’t see a benefit for him when charging at home.
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Old 3 prong 40 amp Kiln outlet and circuit for Tesla charger?
- Thread starter selaing
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The 6-50 is all that is required. No UMC's use the neutral on 240V. For a long run, it saves copper and $. The 14-50 is generally more common. You need to have 6ga wire and a 50 Amp breaker. Then you can charge using up to 80% of the breaker rating which is 40A. The Gen1 UMC can do that. The Gen2 will only draw 32A.
Personally I have two EV circuits and each is a long run so I used 3 conductor Romex and NEMA 6-50's. My cars are dialed back to 30A because that's all we ever need for our driving.
BTW your Tesla will remember your preferred charging rate by location. So you don't have to reset it every time you charge.
Personally I have two EV circuits and each is a long run so I used 3 conductor Romex and NEMA 6-50's. My cars are dialed back to 30A because that's all we ever need for our driving.
BTW your Tesla will remember your preferred charging rate by location. So you don't have to reset it every time you charge.
They are required to be bonded together at the main entrance panel - where the meter is. They are NOT bonded together in a sub-panel. So in the case of a sub-panel, the neutral may very well have a different potential from the safety ground out at the receptacle.
No benefit at home. But a lot of folks carry a 14-50 adapter when on the road. So it is one adapter to buy, rather than two. And in his case all four wires are already there. So no big deal to replace one receptacle with the other.
Then there is a safety issue with the sub panel. The neutral should always have the same potential as ground. The sub panel neutral would only have a different potential from ground if the ground and neutral weren’t bonded properly at the service panel, or it was on the load side of a transformer and the transformer was bonded incorrectly. In those two cases, it would be unlikely that the ground wire would provide a low resistance path the ground anyway.
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The way that is wired is a little bit out of code, but not a big deal to fix. It is supposed to be the green or bare copper wire used for the ground on the 6-50. White is always supposed to be reserved for neutral unless you have no other choice, and then code does allow you to mark the white wire green to show that it's repurposed as a ground. So yeah, you have a couple of easy choices:
1. Keep the 6-50 outlet but remark that white wire.
2. Change it to a 14-50 and use all four wires.
And then buy whatever adapter for the outlet you have.
1. Keep the 6-50 outlet but remark that white wire.
2. Change it to a 14-50 and use all four wires.
And then buy whatever adapter for the outlet you have.
Whether you are allowed to or not depends on the wire type and thickness. Here is a chart about that, which I can explain a bit.
Ampacity Charts - Cerrowire
You only need to pay attention to the first two columns. The first, which has NM-B in the wire types is for what's called Romex cable. That's like the bundle of four wires inside a rubber sheath. That's run directly inside insulated walls. I think that may be what you have. See how it shows that the 8 gauge wires can only allow up to 40A, but the 6 gauge wires can go up to 55? So that would determine if you can move it up to a 50A circuit or not.
For the second column, that is if they are separate wires run in a plastic or metal conduit. That would not be inside your wall, so you will see if that is running along the surface of the walls on the outside. That kind of installation can dissipate heat better, so you'll see the 8 gauge rated for 50A, and the 6 gauge rated for 65A. So if it's that, it's likely you can do the 60A breaker.
...except you can't put a 60A breaker on a 50A outlet. That would only be if they move to an HPWC.
In the "option 1" scenario, if the outlet is connected to a sub-panel, one would also need to change the connection in the panel from the neutral bar to the ground bar.
Um - no. I could go into a long explanation, but besides the National Electrical Code, there are already countless web pages and youtube videos on the topic. Here are a couple to get started:
Subpanels: when the grounds and neutrals should be separated — Structure Tech Home Inspections
Why separate the ground bar from the neutral bar in a sub-panel? - E&S Grounding Solutions
Oh, whoops, you are totally right. I know that, but my brain shifted gears halfway through this when just looking at the wire capabilities, and I forgot about the outlet still being on there. Yes, with either a 6-50 or a 14-50, it still can't go higher than a 50A breaker.
Yeah, I hadn't even gone into why that was wrong before, but thank you. Neutral carries current throughout the house from the 120V circuits, and ground doesn't (shouldn't, unless something is wrong). So that would not be unusual for the neutral to have its voltage pulled a bit away from 0V, while ground should always be pretty solidly there, so they can have a little bit of voltage difference. The bonding at the panel should be holding them close, but at the ends of some wire runs, there will be a little bit.
I’m not arguing with you about that. Sub panels should have isolated grounds and neutrals, so what?
My point is that at the EV outlet the potential between ground and that “white colored wire” identified as a neutral but carrying no current will be zero, assuming everything else is connected right.
You're right, but so what? The outlet has to be wired per code regulations, without regard to what gets plugged in and how that appliance makes use of the power available to it.
Sigh. You are not following the conversation. Yes, the neutral is unused in that particular outlet.
But you had said this:
And we were correcting you on this, that in a subpanel, the neutral can have a little bit different potential from ground, because if that subpanel is feeding a few circuits, including some 120V ones, it can be carrying current on the neutral and can have some different potential at that point.
I have bought a 14-50 outlet. I plan on doing this.
1. Red and Black wires into the right spot.
2. thin copper wire on the ground
3. white wire on the other spot.
We will test a friends mobile charger when he returns. I will also check the gauge of the wire. We will only charge at 32 amps and leave the breaker at 40 amps.
In the event we need to change anything, we would do that the correct way. The outlet is 24 inches from the pannel.
cheers and thanks much
Stu
1. Red and Black wires into the right spot.
2. thin copper wire on the ground
3. white wire on the other spot.
We will test a friends mobile charger when he returns. I will also check the gauge of the wire. We will only charge at 32 amps and leave the breaker at 40 amps.
In the event we need to change anything, we would do that the correct way. The outlet is 24 inches from the pannel.
cheers and thanks much
Stu
Yes, what you have planned sounds good and should be code compliant.
No, it doesn't have to be. NEC allows for this for 40A circuits. There is no 40A outlet type, so what other outlet would one put on a 40A circuit? Ovens do this really frequently, and it's an exception specifically written into the electric code to put a 14-50 or 6-50 onto a 40A rated circuit, using wire and breaker appropriate for a 40A circuit.
And the Tesla UMC is a device that would be appropriate for a 40A circuit, since it only pulls 32A. However, that is a good point that you bring up. For new installs, I don't recommend people to install these 50A receptables on 40A circuits like that because of the potential issue that someone else someday may plug something in expecting it to be a full 50A circuit. So to add a layer of niceness to this, it would be helpful to put some kind of label above the outlet announcing that it is a 40A circuit.
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