High Power Wall Charger (HPWC) vs NEMA 14-50 Direct Plug

[dk92530]

Just an FYI, I am an electrician and an Electrical Engineer so I know a little bit more than most when it comes to chargers and HPWC units. I see posts of people connecting dryer cords and range cords to the HPWC units. All electric devices including EV chargers and the HPWC units are UL listed. This means that they are listed by Underwriters Laboratory to be connected exactly as designed. You have to be cautious of this because installing a cord on a device that is UL listed to be hardwired will invalidate the UL listing on the device. This voids all warranties and can give your insurance company the right to deny the claim if your house catches on fire. All UL listed devices are required to be installed as designed.

The other more technical reason not to do this is that a dryer cord is UL listed and rated for 30 amps and a range cord is UL listed and rated for 50 amps but a dryer usually only has a continuous load of 20 amps and a range usually only draws about 40 amps continuously with all the burners and oven on full. Heating elements in dryers and stoves cycle on and off so the load is never continuous. Electric vehicles chargers are full on until the vehicle is charged.

Using either a dryer cord or a range cord on an HPWC is a surefire way to set the house on fire. Neither cord is designed for the loads presented while charging a vehicle.

 

[mspohr]

Just an FYI, I am an electrician and an Electrical Engineer so I know a little bit more than most when it comes to chargers and HPWC units. I see posts of people connecting dryer cords and range cords to the HPWC units. All electric devices including EV chargers and the HPWC units are UL listed. This means that they are listed by Underwriters Laboratory to be connected exactly as designed. You have to be cautious of this because installing a cord on a device that is UL listed to be hardwired will invalidate the UL listing on the device. This voids all warranties and can give your insurance company the right to deny the claim if your house catches on fire. All UL listed devices are required to be installed as designed.

The other more technical reason not to do this is that a dryer cord is UL listed and rated for 30 amps and a range cord is UL listed and rated for 50 amps but a dryer usually only has a continuous load of 20 amps and a range usually only draws about 40 amps continuously with all the burners and oven on full. Heating elements in dryers and stoves cycle on and off so the load is never continuous. Electric vehicles chargers are full on until the vehicle is charged.

Using either a dryer cord or a range cord on an HPWC is a surefire way to set the house on fire. Neither cord is designed for the loads presented while charging a vehicle.

I have to agree with this. (I am an EE but not an electrician)
When I first got my HPWC, I connected a 50 amp 8 gauge range cord to it because my garage was under construction and I needed options for plugging it in. I ran it at 32 amps and it still got warm to the touch (much warmer than the cable to the car).
After I finished the garage, I hard wired the HPWC to the 6 gauge wire the electrician had installed in the garage. I feel much safer now.

 

[dk92530]

I have to agree with this. (I am an EE but not an electrician)
When I first got my HPWC, I connected a 50 amp 8 gauge range cord to it because my garage was under construction and I needed options for plugging it in. I ran it at 32 amps and it still got warm to the touch (much warmer than the cable to the car).
After I finished the garage, I hard wired the HPWC to the 6 gauge wire the electrician had installed in the garage. I feel much safer now.

Yeah I am sure that the piece of mind makes it easier to sleep at night. I completely understand why people do it. To a lay person it seems that logically it should work. Unfortunately in the real world it isn't.

 

[dk92530]

Or just avoid the decision entirely and get both!

I got the shorter cable version of the HPWC (saves $50), but also have a NEMA 14-50 below the 100A HPWC for instances where I might want to charge outside my garage using the longer UMC.
I have a Model 3 reservation for my wife and prewired the next bay as well for her. HPWCs can share the same circuit and charge simultaneously.
I don’t believe this is true for a NEMA 14-50.
As mentioned before, the HPWC is super convenient. Addition of the cable organizer really helps keep the cable off the floor in a single loop so it stays neat & clean.
View attachment 256414

This may work ok but I would bet that a proper load calculation would show that this setup does not meet code.

Assuming that you have installed 4 guage thhn wire to the sub panel (typical) and the HPWC is set to the maximum which draws 72 Amps and that the Nema 14-50 is on a 50 amp circuit that draws 40 amps and that it is fed by a 100 amp breaker this would not meet code. 4 guage thhn wire for this application is only good for 85 amps. If you installed 2 guage thhn wire (better) this is only good for 115 amps.

For a proper load calculation, because both of these devices (HPWC and the 14-50 outlet) have to be calculated at 100% (because they are intended for a particular appliance such as charging electric vehicles) your application requires a 125 amp circuit feeding the sub panel. This would have to come directly from the main panel because most indoor sub panels do not have 125 amps available.

FYI... The reason that I make these assumptions is that the flexible conduit feeding your sub panel is too small for the proper size wiring.
Yes I did notice that the subpanel appears to be fed from 2 Flexible conduits. They appear to be 1 inch or smaller in size which is still not large enough to safely contain wiring of the proper size.

For this setup to meet code you would have to run at least 1 guage thhn wires from your main service to the subpanel above the HPWC that is fed by a 125 amp breaker. This would allow a continuous load o 125 amps (your setup in full use draws 112 amps).

The argument could be made that only one will be used at a time or that only one breaker would be used at a time but The installation is required to meet code with all of the breakers on and the EV charger plugged into the 14-50 outlet. The most important issue is that if it does not meet code your insurance company could deny the claim if the setup were to cause a fire.

 

[Daniellane]

This may work ok but I would bet that a proper load calculation would show that this setup does not meet code.

Assuming that you have installed 4 guage thhn wire to the sub panel (typical) and the HPWC is set to the maximum which draws 72 Amps and that the Nema 14-50 is on a 50 amp circuit that draws 40 amps and that it is fed by a 100 amp breaker this would not meet code. 4 guage thhn wire for this application is only good for 85 amps. If you installed 2 guage thhn wire (better) this is only good for 115 amps.

For a proper load calculation, because both of these devices (HPWC and the 14-50 outlet) have to be calculated at 100% (because they are intended for a particular appliance such as charging electric vehicles) your application requires a 125 amp circuit feeding the sub panel. This would have to come directly from the main panel because most indoor sub panels do not have 125 amps available.

FYI... The reason that I make these assumptions is that the flexible conduit feeding your sub panel is too small for the proper size wiring.
Yes I did notice that the subpanel appears to be fed from 2 Flexible conduits. They appear to be 1 inch or smaller in size which is still not large enough to safely contain wiring of the proper size.

For this setup to meet code you would have to run at least 1 guage thhn wires from your main service to the subpanel above the HPWC that is fed by a 125 amp breaker. This would allow a continuous load o 125 amps (your setup in full use draws 112 amps).

The argument could be made that only one will be used at a time or that only one breaker would be used at a time but The installation is required to meet code with all of the breakers on and the EV charger plugged into the 14-50 outlet. The most important issue is that if it does not meet code your insurance company could deny the claim if the setup were to cause a fire.

Yes #2
125 AMP Breaker in Main Panel feeding Sub-Panel. Second Conduit feeds Second HPWC.
Was inspected.
NEMA 14-50 Not intended for simultaneous use.
50 AMP Nema14-50 Breaker Always off.
Only intended as backup if HPWCs malfunction or the need to charge outside garage arose.

 

[Rocky_H]

The argument could be made that only one will be used at a time or that only one breaker would be used at a time but The installation is required to meet code with all of the breakers on and the EV charger plugged into the 14-50 outlet.

Not true. That is exactly how you specify it so that it does meet code. If this setup is to not use both at the same time, you don't have to count the load from both together. That is 220.60 of the NEC:

"220.60 Noncoincident Loads. Where it is unlikely that two or more noncoincident loads will be in use
simultaneously, it shall be permissible to use only the largest load(s) that will be used at one time for
calculating the total load of a feeder or service."

 

[liuping]

The other more technical reason not to do this is that a dryer cord is UL listed and rated for 30 amps and a range cord is UL listed and rated for 50 amps but a dryer usually only has a continuous load of 20 amps and a range usually only draws about 40 amps continuously with all the burners and oven on full. Heating elements in dryers and stoves cycle on and off so the load is never continuous. Electric vehicles chargers are full on until the vehicle is charged.

I'm curious why 4 ft 50 AMP rated range cord (which is 6 AWG) would not be able to handle 40Amp continuous.

The UMC cord does not even have 6 gauge wiring, and it charges at 40Amp and is UL approved.

 

[nikolanj]

I just had a 14-50 installed in my garage ($300) and think I will be happy using the UMC for the time being. One question I have is what about buying a second UMC for the car and then being able to leave the original plugged into the the 14-50? I don't know what they cost but could be another way to go?

I am picking up my MS75D tomorrow and have been trying to figure out what to do re: home charging. Like many others, I don't have the ability to home-charge indoors and was considering purchasing a second UMC. If I am reading the Tesla Shop site correctly, the price on the UMC is now $300 (seems like from reading older posts it was at one point $520)? Before I start getting estimates on installing a 14-50 on the outside of my garage, I wanted to make sure I am reading the site correctly and it would be $200 cheaper to go with a second UMC rather than the WC for $500?

The other thought I had (but I'm sure I'm missing something because it seems to simple), is to leave the UMC that comes with the car connected to the 14-50 at home and just bring the J1772 adapter with me when I'm on the road? I figure between the J1772 adapter and the supercharger network, I'd have myself completely covered.... but I know it can't be that easy..... So I guess my question here is what adapters, if any, besides the J1772 would I need on the road? And so long as I am charging at EV charging stations (whether Tesla or otherwise), I would not need my UMC with me, just adapters?

Next question - the house we're renting only has 1 outlet in the garage and right now we have a spare fridge plugged in there. My understanding is that I cannot leave that fridge plugged in at the same time I am charging using the UMC & 5-15 adapter until I can get an electrician out here to install the 14-50 outlet and probably a could of extra household outlets for my own sanity. So questions here are, do I need to unplug the fridge when I'm charging via 5-15? Is the plug on the UMC too large that I couldn't logistically keep both things plugged in at the same time (assuming it were permissible electrically)? And using extension cords are forbidden in this circumstance? If not, what do I need to look for in extension cord specs?

Sorry for all the questions and please pardon my naivete here... and thanks in advance.

 

[Brass Guy]

If you travel outside the supercharger network often, or to places without destination chargers, you might want a second UMC. Otherwise it's probably not necessary. For me, it stays plugged in and once or twice a year I take my UMC with me. Yes, the J1772 adapter stays in the glove box.

If the garage outlet is on a 15A circuit, you can't leave the fridge plugged in while charging. If a 20A circuit I don't know for sure, but probably still an over current situation when the fridge kicks in.
To answer your question though, physically I think you'd be able to get both plugs in.

Tesla says not to use an extension cord. You can use a heavy gauge one, but really should avoid it if possible. On a 5-15 you will need to charge the car many hours (3-4 mph!) while the fridge is off. Probably better to run the fridge on a heavy extension cord from the house if possible, it's not a constant load.

Get the garage electrics updated, you'll be glad when it's done. It'll be expensive if you need trenching. Good luck!

 

[ucmndd]

The other thought I had (but I'm sure I'm missing something because it seems to simple), is to leave the UMC that comes with the car connected to the 14-50 at home and just bring the J1772 adapter with me when I'm on the road? I figure between the J1772 adapter and the supercharger network, I'd have myself completely covered.... but I know it can't be that easy.....

It’s precisely that easy. That’s what I’ve done now for 50k miles. I’ve unplugged the mobile connector and brought it with me for long trips “just in case” less than 10 times. Actually used it away from the house twice.

 

[brkaus]

@nicolanj Depends on where you travel. Most of the time the J1772 is all I bring. If traveling to visit family I bring the portable EVSE.

Around town I simply charge at home. Never go more than 250 miles in a day.

 

[David29]

It’s precisely that easy. That’s what I’ve done now for 50k miles. I’ve unplugged the mobile connector and brought it with me for long trips “just in case” less than 10 times. Actually used it away from the house twice.

Agree. In 30K miles over a period of nearly three years, I have never used the UMC, except to show how it works at car shows or EV events. I have a Wall Connector at home (outdoors).

 

[mspohr]

Depends on where you travel.
I always carry my UMC in the car. I have a HPWC at home.
I've used the UMC many times to destination charge where Superchargers were not available (or convenient).
Destination charging is most convenient. You start the morning with a full charge. I've charged from campground 14-50, motel 6-20, and even motel 120v.
Electricity is nearly ubiquitous. Best be prepared to take advantage of whatever is available.

 

[Tantamount]

I know the consensus here is that the HPWC should perform the same as a 14-50, however, Tesla's own website (Home Charging Installation) shows that using the HPWC on that same 14-50 circuit will get you more miles per hour.

Under "Wall Connector" there is a table. For a circuit breaker that has 50 amps (The same as a 14-50 circuit), the maximum output is 40 amps so the power wall adapter is supposed to generate 37 miles/hr for the Model 3, 29 miles per hour for the Model S, and 25 miles per hour for the Model X.

However, under "Outlets and Adapters", the NEMA 14-50 shows 30 for the Model 3, 23 for the Model S, and 20 for the Model X. This is equal to the 40 circuit breaker /32 amps out table entry under "Wall Connector".

Is there a hard limit of 32 amps for Teslas when connecting using adapters that can only be overcome using the HPWC, or are there table entries for HPWC that are purely theoretical?

 

[brkaus]

I know the consensus here is that the HPWC should perform the same as a 14-50, however, Tesla's own website (Home Charging Installation) shows that using the HPWC on that same 14-50 circuit will get you more miles per hour.

Under "Wall Connector" there is a table. For a circuit breaker that has 50 amps (The same as a 14-50 circuit), the maximum output is 40 amps so the power wall adapter is supposed to generate 37 miles/hr for the Model 3, 29 miles per hour for the Model S, and 25 miles per hour for the Model X.

However, under "Outlets and Adapters", the NEMA 14-50 shows 30 for the Model 3, 23 for the Model S, and 20 for the Model X. This is equal to the 40 circuit breaker /32 amps out table entry under "Wall Connector".

Is there a hard limit of 32 amps for Teslas when connecting using adapters that can only be overcome using the HPWC, or are there table entries for HPWC that are purely theoretical?

The Gen2 EVSE has a 32a max. The Gen1 has a 40a max.

They started shipping the Gen2 cords with the model 3 and also shifted S/X around the same time.

Advantage of the Gen2 is more adaptors are available for that model.

 

[ucmndd]

I know the consensus here is that the HPWC should perform the same as a 14-50, however, Tesla's own website (Home Charging Installation) shows that using the HPWC on that same 14-50 circuit will get you more miles per hour.

Under "Wall Connector" there is a table. For a circuit breaker that has 50 amps (The same as a 14-50 circuit), the maximum output is 40 amps so the power wall adapter is supposed to generate 37 miles/hr for the Model 3, 29 miles per hour for the Model S, and 25 miles per hour for the Model X.

However, under "Outlets and Adapters", the NEMA 14-50 shows 30 for the Model 3, 23 for the Model S, and 20 for the Model X. This is equal to the 40 circuit breaker /32 amps out table entry under "Wall Connector".

Is there a hard limit of 32 amps for Teslas when connecting using adapters that can only be overcome using the HPWC, or are there table entries for HPWC that are purely theoretical?

The new gen 2 mobile connector, which has been included with cars for the last 6-12 months, is limited to 32 amps, not 40 like the prior gen 1 unit. That's why Tesla is showing the lower charge rate in that column.