New UMC 14/50 limited to 32 amps... WHY?!

[mknox]

I totally agree the lowering came because people have bad wiring, codes not strong enough or clear enough for wiring NEMA 14-50 and people trying to save money on wiring (and home grown "electricians" that connect whatever makes it appear to work).

1. US and Canadian electrical codes have language around ratings for "continuous loads". EVs draw power continuously unlike stoves, dryers or heaters that cycle on and off and provide some time for cooling. That is why they are rated at 80% of the circuit rating.

2. In Canada, and I believe in the US it is common and permissible under code to wire a NEMA 14-50 to a 40 amp breaker with wiring rated for 40 amps. Most, if not all electric stove outlets are wired this way. If you pulled 40 amps continuous on a circuit like this and the breaker didn't trip (as it should) you could end up with overheated wiring. This has nothing to do with shoddy wiring.

From a safety perspective, it makes sense to rate the UMC for "lowest common denominator" situations. Not everyone who uses these things will be as savvy as folks around here and I personally put safety above all else. If you want or need more than 32 amps, simply get a HPWC or other EVSE and hard-wire it in to the rating you desire. Simple.

 

[whitex]

1. US and Canadian electrical codes have language around ratings for "continuous loads". EVs draw power continuously unlike stoves, dryers or heaters that cycle on and off and provide some time for cooling. That is why they are rated at 80% of the circuit rating.

2. In Canada, and I believe in the US it is common and permissible under code to wire a NEMA 14-50 to a 40 amp breaker with wiring rated for 40 amps. Most, if not all electric stove outlets are wired this way. If you pulled 40 amps continuous on a circuit like this and the breaker didn't trip (as it should) you could end up with overheated wiring. This has nothing to do with shoddy wiring.

From a safety perspective, it makes sense to rate the UMC for "lowest common denominator" situations. Not everyone who uses these things will be as savvy as folks around here and I personally put safety above all else. If you want or need more than 32 amps, simply get a HPWC or other EVSE and hard-wire it in to the rating you desire. Simple.

Yea, the continuous load code is incomplete and fraught with safety issues. It should only apply to a single run (Single socket at end of a circuit) and require the circuit to match the socket. As soon as you allow lower circuit rating (breakers ok to be lower, but wires should be sized for socket rating), or if you have more than one socket on a circuit, the circuit should be sized to sustain 100% because 4 loads at 25% still add up to a 100%.

I agree with you that Tesla made the decision to ramp down for safety. I would have done the same, except maybe let the new car buyers choose between UMC or HPWC for new cars without extra charge (maybe create a 50A HPWC if it saved money).

 

[yuhong]

I am surprised that circuit breakers at things like RV parks was not mentioned in this thread. In general 30-32A is becoming the de-facto standard for level 2 for this and other reasons.

 

[mspohr]

The "Mobile" connector is designed for occasional use when traveling. It's not designed for daily use especially with the 14-50 socket which are prone to failure due to cheapness.
For home charging, get a HPWC.

 

[TexasEV]

The "Mobile" connector is designed for occasional use when traveling. It's not designed for daily use especially with the 14-50 socket which are prone to failure due to cheapness.
For home charging, get a HPWC.

Not true. Mobile is a capability, not a requirement. This is one of Tesla’s recommended methods of home charging. Tens of thousands of Tesla owners use it for daily use.

 

[mspohr]

Not true. Mobile is a capability, not a requirement. This is one of Tesla’s recommended methods of home charging. Tens of thousands of Tesla owners use it for daily use.

And occasionally, they burn out a cheap/defective 14-50 socket (and hopefully don't start a fire) by running it at 40 amps. Hence Tesla's reducing the current to 32 amps.

 

[Uncle Paul]

Had this issue with my 14-50.

Electrician ran out of pro quality sockets. Stopped on the way to the job and picked up a cheapie at Home Depot.

The box felt warm when charging, and the socket began to degrade at the connections.

He took a look and acknowledged his error and replaced the warm socket with a new pro quality socket. Now charges cool as a cucumber.

See many posts from people wanting to install their home chargers as cheaply as possible, but believe it would be good practice to error on the side of quality rather than price.

 

[scottm]

Get a Hubble brand or other industrial grade socket for the wall if you're using 14-50 with UMC and routinely un/plugging. The cheapo Depot socket for stoves is really not meant to be un/plugged constantly.

If you have a cheapo wall socket one mitigation you could do is leave the Tesla 14-50 plug adapter portion plugged into the wall socket and just detach and take the rest of the UMC with you and snap on another adapter... if say, you're doing 120V at work all day.

 

[mknox]

I agree with you that Tesla made the decision to ramp down for safety. I would have done the same, except maybe let the new car buyers choose between UMC or HPWC for new cars without extra charge (maybe create a 50A HPWC if it saved money).

Not a horrible idea, but I think most people would want a UMC for travelling. Perhaps less so now than when I bought my car 5 years ago and EVSE stations were few and far between, but still...

 

[davewill]

Get a Hubble brand or other industrial grade socket for the wall if you're using 14-50 with UMC and routinely un/plugging. The cheapo Depot socket for stoves is really not meant to be un/plugged constantly.

If you have a cheapo wall socket one mitigation you could do is leave the Tesla 14-50 plug adapter portion plugged into the wall socket and just detach and take the rest of the UMC with you and snap on another adapter... if say, you're doing 120V at work all day.

Honestly, anyone who knows they have a questionable installation should run, not walk, to get it corrected. Mitigation should NOT be on the table.

 

[whitex]

Not a horrible idea, but I think most people would want a UMC for travelling. Perhaps less so now than when I bought my car 5 years ago and EVSE stations were few and far between, but still...

Well, for travel 32A is the safe limit, as in your travels you may encounter those NEMA-14-50's with only 40A breakers on 40A circuits (since they are legal and up to code).

 

[whitex]

Honestly, anyone who knows they have a questionable installation should run, not walk, to get it corrected. Mitigation should NOT be on the table.

The installations that cause a problem are legal and follow the code, hence the issue. If you have bad wiring and a Tesla charger burns your house down, your fault. If you have an up to code plug and same happens, you blame Tesla.

 

[davewill]

The installations that cause a problem are legal and follow the code, hence the issue. If you have bad wiring and a Tesla charger burns your house down, your fault. If you have an up to code plug and same happens, you blame Tesla.

Who cares about blame? If you know your outlet is questionable, you get it fixed, you don't play games with leaving adapters plugged into the wall.

 

[iffatall]

The "Mobile" connector is designed for occasional use when traveling. It's not designed for daily use especially with the 14-50 socket which are prone to failure due to cheapness.
For home charging, get a HPWC.

What is the basis for this statement? When I bought my car this was one of two recommended methods by Tesla for daily charging. I don't use it for daily charging myself, but this is the first time I see someone mention this is not for daily use.

I was even advised by Tesla to buy an additional UMC so that I don't have to keep unplugging every time I am on a trip. One can stay plugged into the wall and one can stay in the trunk. I did not heed the advice, but that was what was suggested.

 

[TexasEV]

He has no basis for that statement. It’s not the first time he’s expressed that opinion as fact. You’re entirely correct that Tesla shows UMC as a home charging option, with extensive documentation on the web site about installing home NEMA 14-50, etc.

 

[mspohr]

He has no basis for that statement. It’s not the first time he’s expressed that opinion as fact. You’re entirely correct that Tesla shows UMC as a home charging option, with extensive documentation on the web site about installing home NEMA 14-50, etc.

Yes, I guess Tesla does recommend the mobile connector for home charging. Probably why the cut the amperage down to 32 so people wouldn't burn up their sockets (and houses).

 

[whitex]

Who cares about blame?

Tesla does as do their investors. Liability, lawsuits, money... all that stuff you might not care about.

If you know your outlet is questionable, you get it fixed, you don't play games with leaving adapters plugged into the wall.

Easier said than done for some people.

1. Most people who have those don't "know" since their electrician and inspector said it's up to code, they have no choice but to trust them since they simply don't know any better. If they have a friend with a Tesla who also isn't aware of this, I bet they'd rather the Tesla mobile charger was limited to 32A.
2. Even if they find out, "fixing" it would not be covered under any kind of builder and/or electrical work warranty, since it's up to code. Fixing this may be very costly. Say they have such NEMA-14-50 on 40A , the cost of wiring a new 50A circuit could be $1K-$5K. Most people don't want to spend that kind of money for a friend or family member who might visit one day. 50A is not needed for an oven or dryer, but if they ever have a friend with a Tesla with an old 40A charger who wants to plug in through an extension cord sticking out the window, it would be good to have it upgraded. Or you could just ask the friend to crank down the charging current to 32A. Or, might be cheaper to buy and install an HPWC or even just a proper additional NEMA-14-50 in the garage right next to the breaker panel on a 50A , 3ft long circuit.

Bottom line is there are already existing NEMA-14-50's out there that will not be rewired, hence the problem cannot be avoided. The only way to fix this long term is to come up with a whole new 50A NEMA socket, make sure the code says you have to supply it with a 50A circuit, then Tesla can sell an adapter to that socket which will allow 40A draw.

 

[Daniellane]

Gen1 UMC no longer availabile at Tesla online Store.
So this appears to be a gen2 style 40AMP Charger with a dedicated 14/50 plug.
Anyone have additional insight on this? GEN2 benefits beyond flat plug?
Model S/X Corded Mobile Connector

 

[miimura]

The Corded Mobile Connector has been around for quite a while. Maybe Fall 2016? I suppose it could be called a Gen 1.5 device because it has a thermal monitor in the plug like the Gen2. It does deliver the full 40 amps to the car.

 

[whitex]

Why is the corded one so much more expensive? Is it 40A vs. the one with adapters 32A? Couldn't find it in the description.