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20 or 30 amp breaker for tesla wall charger

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The forums are full of posts of the Leviton charring wires or cracking over time, or worse. The Leviton is deigned to be used occasionally, such as with a welder, it is not designed for continuous use. The UMC will pull 32A for many hours continuously. Search the forums and make you own decision.
The Leviton is indeed cheaply made however there is no problem with it for continuous use and it is designed for that. What it is not designed for is frequently being plugged/unplugged. The issue with cheaper sockets is that they cannot stand up to being unplugged/plugged . It is this mechanical action that wears them out or causes them to fail. The same applies to the cheap outlets in your house.

More expensive outlets, sometimes listed as commercial grade but that has no legal or technical standard attached, have a higher quality construction that stands up longer to being plugged and unplugged.

The length of time the current is running through it has nothing to do with the mechanical aspect of the socket.

Short answer:
If you intend to frequently plug and unplug your EVSE get a higher quality outlet than a cheap Leviton.
If you intend to leave your EVSE plugged in continuously only rarely unplugging it a cheap Leviton socket is fine.

I went with the second option for both our EVSE’s and 11 months later the Leviton sockets are fine despite pulling 40 amps every night.
 
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If you set the Wall Connector to, for example, a 30 amp circuit you need to use a 30 amp breaker. Whatever you choose the max charging rate will be 80% and the wall connector, if properly configured, will manage this. On this 30 amp example it will charge the car at 24 amps.
I have my wall connector fed from a 50 amp breaker, but I set the wall connector for 24 amps, because of other devices connected to the system. Everything has worked great, except I have to keep an eye on it, because every now and then, perhaps monthly or a few weeks, the wall connector will reset to 48 amps. It hasn't ever caused the main breaker to trip. But the total of A/C, microwave, induction cooktop, toaster, water heater, clothes dryer, etc., would certainly trip the main if they all happened to be on at the same time that the wall connector tried to charge at 48 amps. I set the car charger at 24 A, but that has to be reset for every charging session. The wall connector should stay locked at 24. Perhaps software updates from the mother ship cause it to reset to default?
 
The forums are full of posts of the Leviton charring wires or cracking over time, or worse. The Leviton is deigned to be used occasionally, such as with a welder, it is not designed for continuous use. The UMC will pull 32A for many hours continuously. Search the forums and make you own decision.
It is the Leviton 14-50R model # 279-S00 (found at home improvement centers) that has been known to overheat, potentially cause electrical fires.

Master Thread: Definitive 14-50 NEMA Outlet Guide
 
The maximum amperage rating of the circuit, circuit breaker can't exceed the maximum amperage rating of the wire used in the circuit.

The maximum amperage rating of the wire used in a circuit can exceed the maxim amperage rating of the circuit breaker.
This. You can always use a heavier gauge wire than that required by the breaker, or the outlet, or the load if you want to for some reason.
 
It is the Leviton 14-50R model # 279-S00 (found at home improvement centers) that has been known to overheat, potentially cause electrical fires.

Master Thread: Definitive 14-50 NEMA Outlet Guide
The problem as I understand it is that the plug contact resistance increases over time (especially if unplugged a lot) due to wear and oxidation and this causes heat to be generated where they touch, which melts the socket, burns the contacts, and makes the situation even worse. Higher quality outlets minimize this but it never goes away completely.

A hard wired charger is safer in this regard.
 
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Those threads and linked videos on YouTube have a common theme:

1) the wires were not tightened correctly. Most of the time this seems to be due to a DIY installation by someone with no experience of high current wiring (or maybe any wiring). What else did they not do to code?

2) the outlet has a device plugged and unplugged into it many times. Which *is* a problem for cheaper outlets.

3) no evidence is presented of any fault using a correctly installed Leviton outlet with a near permanently plugged in EVSE. There are plenty of posts with caveats “I don’t have a thermometer but”, “I switched to a different brand and now the plug feels a little cooler, but it’s not summer any more”, “I’ve been using this outlet to charge my EVs with no problems for years but”, “the receptacle prongs look too small in my opinion”, “the screw downs look better to me”.

I’m not saying it’s not a good idea to buy a better quality socket, it”s always a good idea to go with a better quality anything. But I don’t like blanket statements that X is not suitable or not designed for something when that is nothing more than opinion. The installation matters far more than the brand of outlet and the grade of outlet needs to be selected based on the mechanical duty cycle it’s going to be put through. All 14-50 outlets are designed and tested to handle continuous 40 amp loads based on correct installation. The number of times something is plugged and unplugged will dictate how quickly the socket wears out and becomes dangerous. And so called “industrial” ones will last far longer. (There is no legal or technical specification to be met to label something industrial however so be careful).

If you do a DIY install with any socket you are increasing your fire risk because chances are you don’t know what you’re doing when it comes to the details that matter.
If you buy a cheap socket and work it hard by plugging stuff in and out every day you are increasing your fire risk.
If you have the install done with a quality socket by a paid professional who is not very good at his job, you are increasing your fire risk.

As a side note: Electric ovens can suck down 5kW, the large rings on your top another 3kW, even the small ones are about 1.5kW. You likely do not have an industrial grade socket for your oven because you rarely unplug it and plug it in. They last for many many years. It’s not a problem.
 
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So, I'm going to summarize, like half the other posters here.
  1. The OP is using 6 AWG wire, likely ROMEX. Tracked down the spec from Southwire: It's here. I'm an engineer: I like PDFs. This stuff is sold at Lowes, by the foot, even. Max temperature of use is 90C, 194F, dry locations (not underground). 55A Allowable Ampacity. Which means that using a 50A breaker on it is fine, but not a 60A breaker.
  2. I don't know why people started talking about 8 AWG wire. 8 AWG ROMEX is rated for 40A. The OP didn't use 8 AWG wire in the first place. Now, for a hypothetical: Had the OP and his buddy wanted to save a bit of money, they could have used 8AWG ROMEX. They would have had to label the NEMA14-50 socket with a 40A label (to meet code) and have used a 40A GFCI circuit breaker. At the end of all this, it would have worked just fine with the UMC. But our man used 6 AWG, which matches the NEMA14-50 for current and, after making his run to the local electrical supply source, will have a GFCI 50A breaker, so all will be sweetness and light.

Now for a bit more info. First of all, wire. Wire has resistance. Per unit length, even. Run current through a wire and the power dissipated in that wire goes as current*current*resistance, or I^2*R.

OK: Hang a piece of naked wire in mid air, run current through it, and it'll keep on conducting current until the point where it melts. Melting point of copper is 1084C. Resistivity of copper is around 1.5 Ohm-meter x 10**-8. Actual resistance of a piece of copper wire is R = (Resistivity * length_of_wire)/(diameter_of_wire *diameter_of_wire*3.14159/4).

I've actually had to get the temperature along the length of a piece of silver wire, once upon a time; the equations get nasty, because the wire radiates thermal energy (hello, IR!), gets thermal energy from the environment into it, and because there's physical conduction out of and in to the wire from the surrounds as well. But a naked piece of 6 AWG wire can probably conduct hundreds of amps before the sucker melts.

So, why this 55A limit? Because the UL and other wire manufacturers don't want the insulation to heat up and char. Charred insulation conducts current. Which gets one more heating. Which chars the wire even more, and House Fires R Us.

The spec on that 6-3 ROMEX says, "90C wire", which means that, under normal building practices, the heat increase due to the rated current won't get the wire above 90C, at which point the the insulation begins to degrade.

That spec works both ways, though: The people doing the install, to be safe, have to guarantee that the environment isn't going to result in that wire getting too hot. Wrapping 6-3 ROMEX around a hot water boiler is right out. (And the wiring harnesses attached to jet turbine engines have ratings that are in the "other" realm.) But, interestingly, running that wire through an environment that can't conduct heat is right out, too.

In addition, that resistance equation I mentioned above (R = rho*length/area) means that the resistance goes up with length. Ohms law says that, for a given amount of current, V = I * R; so, as that wire gets longer and longer the voltage at the end gets lower and lower; make it long enough (a mile?) and most of the power leaving the breaker is simply heating up the wire (albeit, a long wire). Which is another factor: Long runs for a given current rating are required to use a bigger gauge wire (smaller AWG number) to keep the voltage drop and power dissipation in the wire under control.

This is where electricians earn their money: They know all this stuff backwards and forwards: Insulation ratings, fire retardant ratings, heat rise, etc., to come up with a solution that's (a) cheap and (b) meets safety standards. Now, a 15' length of ROMEX is not going to delve into Higher Math, at least if one is careful. But if the breaker panel on a house is 150' from the charge point, well.

By the by: If one hasn't figured this out by now, this whole business about wire resistance and power dissipation is Why High Tension Wires. Generally, Power = Voltage * Current, but the losses in the wire go as Current*Current*Resistance. So, if one wants to move, say, 10 MW of energy from point A to B, doing so at 400 VAC nets one 10e6/400 = 25,000 A; doing so at 15 kV nets one 10e6/15e3 = 666 A, and a lot less losses in the wire one is using. There are limits to everything, though: Use the right kind of transformer to boost the transmission line voltage to gigantic levels (and the current to miniscule levels) eventually starts breaking down air molecules due to the high tension (corona discharge) which loses one energy that way. Not to mention actually radiating energy away, a la radio waves. Don't know if you guys know this, but in NYC, there are no-kidding power links in Manhattan that use superconductors that, if memory serves, are kept cold with liquid nitrogen. Take that, Ohm's Law!

Next thing: The difference between NEMA14-50's of the "cheap" variety and the "expensive" variety. As one might expect, just like with power dissipation in wire, it all comes down to heat and Not Melting/Blowing Things Up. So, right off: Take a spanking new Leviton NEMA14-50 and some higher quality variant from somewhere else. Plug them both in, run 40A steady through both of them, and they'll both last forever. So, what's the difference then?

Has to do with unplugging connectors. Two things:
  1. Wear. Run two metals next to each other and they abrade. Metals that have low resistance tend to have silver, gold, or other strange materials that either don't corrode (much) or have low resistivity. The Good Stuff (a) costs more and (b) is softer. So, a good, cheap (ha! pick one) socket from ye mass-market manufacturer is going to put as little of those fancy metals in there as the market will bear. How they get away with it: Claiming that the socket goes in, once (a la one's kitchen stove) and not back out again in the foreseeable future. What about somebody with a UMC who's always throwing the thing in the trunk in case they have to charge on the road? Oops. Wear out the soft metals, expose the base, doesn't conduct so well metals, and Flames R Us. Solution: More surface area, less force required to get the requisite low resistance, better (more expensive) metals, and it'll wear less and last longer. This ain't rocket science.
  2. There's a special case: Unplugging a socket while it's carrying current. All of you out there who play with vacuum cleaners of the non-Roomba type know the drill: Pull the cord while the vacuum cleaner is running results in an arc at the socket. Basically, there's all these big magnetic fields in an electric motor that store energy. Pull the cord and that energy has to go somewhere, magnetic fields not known for storing energy very well, and that's the arc. Likewise, pull a NEMA14-50 while the load is carrying current is going to cause an arc at the contacts. An arc is a blinkin' lightning bolt, temperatures are sun-hot and, yeah, it's plasma. It will vaporize those spiffy cool metals that we were just talking about and deposit the stuff elsewhere. This pits the contacts and makes them not work so well no more. A cheapie NEMA14-50 won't faint and die the first time one does this, or even the second, but, with the bigger contact area on the Good Type of a NEMA14-50, the Good One will last a lot longer.
Enough for the weekend.
 
So, I'm going to summarize, like half the other posters here.

Im going to tease you a bit, because I love reading your posts. I feel like I learn something every time I read one, so this is really "good natured teasing". With that being said, only an engineer (or possibly a teacher) would say "I'm going to summarize" then proceed with a post the size of that resultant post :)

(again, ment to be good natured, not mean spirited).
 
With all the really great recommendations and information herein, I thought I'd add my 2cents just in case it might help.

I decided that my outlet would be certainly providing a lot of power, perhaps for several hours a day. And certainly for years to come. I did not scrimp on the quality of breakers, wires, outlets, etc. I believe the extra $100-$200 or so to use proper quality materials will pay for itself in the long run.

What would you be thinking if some years in the future the wire or breaker or outlet failed and started a fire. Would those extra dollars today, mean much then?

But you do have a budget that may well be much different than mine. So do what you can, as best you can. In no way should you install something that is not up to code.

My 2cents anyway. Good luck.
 
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So, I'm going to summarize, like half the other posters here.
  1. The OP is using 6 AWG wire, likely ROMEX. Tracked down the spec from Southwire: It's here. I'm an engineer: I like PDFs. This stuff is sold at Lowes, by the foot, even. Max temperature of use is 90C, 194F, dry locations (not underground). 55A Allowable Ampacity. Which means that using a 50A breaker on it is fine, but not a 60A breaker.
  2. I don't know why people started talking about 8 AWG wire. 8 AWG ROMEX is rated for 40A. The OP didn't use 8 AWG wire in the first place. Now, for a hypothetical: Had the OP and his buddy wanted to save a bit of money, they could have used 8AWG ROMEX. They would have had to label the NEMA14-50 socket with a 40A label (to meet code) and have used a 40A GFCI circuit breaker. At the end of all this, it would have worked just fine with the UMC. But our man used 6 AWG, which matches the NEMA14-50 for current and, after making his run to the local electrical supply source, will have a GFCI 50A breaker, so all will be sweetness and light.

Now for a bit more info. First of all, wire. Wire has resistance. Per unit length, even. Run current through a wire and the power dissipated in that wire goes as current*current*resistance, or I^2*R.

OK: Hang a piece of naked wire in mid air, run current through it, and it'll keep on conducting current until the point where it melts. Melting point of copper is 1084C. Resistivity of copper is around 1.5 Ohm-meter x 10**-8. Actual resistance of a piece of copper wire is R = (Resistivity * length_of_wire)/(diameter_of_wire *diameter_of_wire*3.14159/4).

I've actually had to get the temperature along the length of a piece of silver wire, once upon a time; the equations get nasty, because the wire radiates thermal energy (hello, IR!), gets thermal energy from the environment into it, and because there's physical conduction out of and in to the wire from the surrounds as well. But a naked piece of 6 AWG wire can probably conduct hundreds of amps before the sucker melts.

So, why this 55A limit? Because the UL and other wire manufacturers don't want the insulation to heat up and char. Charred insulation conducts current. Which gets one more heating. Which chars the wire even more, and House Fires R Us.

The spec on that 6-3 ROMEX says, "90C wire", which means that, under normal building practices, the heat increase due to the rated current won't get the wire above 90C, at which point the the insulation begins to degrade.

That spec works both ways, though: The people doing the install, to be safe, have to guarantee that the environment isn't going to result in that wire getting too hot. Wrapping 6-3 ROMEX around a hot water boiler is right out. (And the wiring harnesses attached to jet turbine engines have ratings that are in the "other" realm.) But, interestingly, running that wire through an environment that can't conduct heat is right out, too.

In addition, that resistance equation I mentioned above (R = rho*length/area) means that the resistance goes up with length. Ohms law says that, for a given amount of current, V = I * R; so, as that wire gets longer and longer the voltage at the end gets lower and lower; make it long enough (a mile?) and most of the power leaving the breaker is simply heating up the wire (albeit, a long wire). Which is another factor: Long runs for a given current rating are required to use a bigger gauge wire (smaller AWG number) to keep the voltage drop and power dissipation in the wire under control.

This is where electricians earn their money: They know all this stuff backwards and forwards: Insulation ratings, fire retardant ratings, heat rise, etc., to come up with a solution that's (a) cheap and (b) meets safety standards. Now, a 15' length of ROMEX is not going to delve into Higher Math, at least if one is careful. But if the breaker panel on a house is 150' from the charge point, well.

By the by: If one hasn't figured this out by now, this whole business about wire resistance and power dissipation is Why High Tension Wires. Generally, Power = Voltage * Current, but the losses in the wire go as Current*Current*Resistance. So, if one wants to move, say, 10 MW of energy from point A to B, doing so at 400 VAC nets one 10e6/400 = 25,000 A; doing so at 15 kV nets one 10e6/15e3 = 666 A, and a lot less losses in the wire one is using. There are limits to everything, though: Use the right kind of transformer to boost the transmission line voltage to gigantic levels (and the current to miniscule levels) eventually starts breaking down air molecules due to the high tension (corona discharge) which loses one energy that way. Not to mention actually radiating energy away, a la radio waves. Don't know if you guys know this, but in NYC, there are no-kidding power links in Manhattan that use superconductors that, if memory serves, are kept cold with liquid nitrogen. Take that, Ohm's Law!

Next thing: The difference between NEMA14-50's of the "cheap" variety and the "expensive" variety. As one might expect, just like with power dissipation in wire, it all comes down to heat and Not Melting/Blowing Things Up. So, right off: Take a spanking new Leviton NEMA14-50 and some higher quality variant from somewhere else. Plug them both in, run 40A steady through both of them, and they'll both last forever. So, what's the difference then?

Has to do with unplugging connectors. Two things:
  1. Wear. Run two metals next to each other and they abrade. Metals that have low resistance tend to have silver, gold, or other strange materials that either don't corrode (much) or have low resistivity. The Good Stuff (a) costs more and (b) is softer. So, a good, cheap (ha! pick one) socket from ye mass-market manufacturer is going to put as little of those fancy metals in there as the market will bear. How they get away with it: Claiming that the socket goes in, once (a la one's kitchen stove) and not back out again in the foreseeable future. What about somebody with a UMC who's always throwing the thing in the trunk in case they have to charge on the road? Oops. Wear out the soft metals, expose the base, doesn't conduct so well metals, and Flames R Us. Solution: More surface area, less force required to get the requisite low resistance, better (more expensive) metals, and it'll wear less and last longer. This ain't rocket science.
  2. There's a special case: Unplugging a socket while it's carrying current. All of you out there who play with vacuum cleaners of the non-Roomba type know the drill: Pull the cord while the vacuum cleaner is running results in an arc at the socket. Basically, there's all these big magnetic fields in an electric motor that store energy. Pull the cord and that energy has to go somewhere, magnetic fields not known for storing energy very well, and that's the arc. Likewise, pull a NEMA14-50 while the load is carrying current is going to cause an arc at the contacts. An arc is a blinkin' lightning bolt, temperatures are sun-hot and, yeah, it's plasma. It will vaporize those spiffy cool metals that we were just talking about and deposit the stuff elsewhere. This pits the contacts and makes them not work so well no more. A cheapie NEMA14-50 won't faint and die the first time one does this, or even the second, but, with the bigger contact area on the Good Type of a NEMA14-50, the Good One will last a lot longer.
Enough for the weekend.
I use Romeo 6/3 with nema 14/50 plugs Hubbell brand , and double 50amp breaker to charge model Y 30 hours with Tesla mobil charge about 2 months , do no use 60amp breaker
 
If this is your home charging (permanent) setup I would remove the 14-50, install a Tesla wall connector hard wired to your 60 amp circuit, and enjoy charging safely at the full 48 amps the car is capable of. This would also allow you to keep mobile charger in the car to use when it’s needed in other locations.
 
@davewill is of course correct. Here is the case for a wall connector, anyway:

  • The wall connector will charge at 40A on a 50A circuit, the mobile connector is limited to 32A
  • If you upgrade the wire to a 60A circuit the wall connector will charge at 48A
  • The wall connector does not require a GFCI breaker
  • The cable for the wall connector is 24’ versus 20’ for the mobile connector
  • The wall connector is water proof
  • The wall connector allows you to restrict who can use it (useful for outside installations)
  • If you add a second wall connector in the future, the wall connector has power sharing built-in
  • The wall connector’s firmware is updated via the internet. The two items noted above were added via firmware updates.
  • Having both a wall connector and mobile connector means you can keep the mobile connector in the car, as opposed having to remember to take it with you when needed
  • The wall connector requires only 2-conductor wire while the 14-50 option requires 3, so you can save some money there
 
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