Charging two Teslas at once?

[ac_power]

OK, service capacity is a factor of course, but suggesting to everyone a solution which is based on particular limitation, is clearly a mislead. Most households have 100+A service, which means minimum 70..75A can be pulled safely in the night time. So separate branches may be way to go, exactly to avoid complications of 80..90A rated circuits, still pulling decent combined current.
And best bang for the buck would be a $15 NEMA 14-50 with Gen1 UMC (40A), compared to $500 HPWC (48A). Even Gen2 (32A) looks fine given that price differential.
Talking about safety switch, I don't think that extra wire length will be needed. It mounts upstream of existing outlet/HPWC, so cutting will be required rather than extension. And output wire is a separate piece anyway.

 

[brkaus]

Just to reiterate, I'm advocating for using #4 by default even at 48A. Don't think current rating may be a concern even after Tesla re-enables 70..80A charging rate.
Would be more interesting to see what everyone thinks about dual HPWC load sharing from single #6 wire, that has been promoted here as one of best solutions.

I have one HPWC on #6 THNN. Going to add a second on the same circuit. Have a 50a breaker and a separate EV meter. I can charge off peak for $30/mo as long as I stay below 50a.

 

[whitex]

OK, service capacity is a factor of course, but suggesting to everyone a solution which is based on particular limitation, is clearly a mislead. Most households have 100+A service, which means minimum 70..75A can be pulled safely in the night time. So separate branches may be way to go, exactly to avoid complications of 80..90A rated circuits, still pulling decent combined current.
And best bang for the buck would be a $15 NEMA 14-50 with Gen1 UMC (40A), compared to $500 HPWC (48A). Even Gen2 (32A) looks fine given that price differential.
Talking about safety switch, I don't think that extra wire length will be needed. It mounts upstream of existing outlet/HPWC, so cutting will be required rather than extension. And output wire is a separate piece anyway.

I think what most people do, in order of cost and complexity:

1. 50A breaker using AWG6 to NEMA 14-50, use mobile connector to charge, 32A or 40A charging
2. Hardwire HWPC instead of NEMA 14-50, upgrade breaker to 60A - 48A charaging
3. For second car, add another HWPC on the same 60A breaker, using AWG6 - this creates a nice 2 car system with 48A charging shared
4. If you need more, and your house service can take it, run AWG2, add safety disconnect and upgrade the one or two HPWCs to 100A circuit, resulting in an 80A shared system.

Bottom line is that 48A charging is sufficient for most people with one or two Teslas, so most people will never need #4. What you are suggesting is step 3.5, which is kind of neither here or there since if 48A is insufficient for you, you do quiet a bit of driving and probably could use all you can get, which is the full 80A - there probably aren't that many people who need charging in between. Maybe you are in that range, need more than 48A but 80A is not needed, so I'm not saying you are wrong, just that for most people, AWG6 60A circuit is most benefit for least hassle.

Most households have 100+A service, which means minimum 70..75A can be pulled safely in the night time.

With 100A serving no you can't. AC kicking in, hot tub, whole house steam humidifier - you would be going to the breaker box often when those kick in. Worst of all, you have to remember to plug your cars only just as the last person goes to sleep. Pain in the ass at the very least. If you can have a shared 48A (or for 100A service, maybe even 40A) which can be used even during the day, it's much more convenient - just plug in whenever you're home.

 

[jerry33]

FWIW. 1970s house. 200 amp service (upgraded during my ownership of the house). 85S and Leaf. 14-50 and Clipper Creek 32 amp. Tesla charging set to start at 02:00. Leaf charging set to end at 05:00. The charging times overlap. Sometimes the Tesla will drop from the 33 amp setting to 30 amps, but that did not start when the Leaf was acquired. The power where I live is rather flakey. The lights flickered--long ago when they were incandescent. Electricians say it's everywhere in the area where I live due to old infrastructure which is not likely to be upgraded. A 6 KVA UPS takes care of all the electronics (every room but the kitchen has at least one UPS controlled outlet). The only gas items are the tankless water heater (almost twenty years old now) and the heating.

 

[ac_power]

3. For second car, add another HWPC on the same 60A breaker, using AWG6 - this creates a nice 2 car system with 48A charging shared

Assuming 11.5 KW charging for 8 hrs with 80% efficiency, max overnight capacity will be ~74 KWh to the battery, split between two cars. Sounds marginal.
How about this:
1. NEMA 50A breaker on #4;
2. 60A breaker, HPWC;
3a. Add safety SW, upgrade breaker when Tesla re-enables higher currents on the cars;
3b. 90A breaker with safety SW, add 2nd HPWC, 72A load sharing.
All using original #4 wiring. Maximum configuration only 10% lower than yours with #2.

With 100A serving no you can't. AC kicking in, hot tub, whole house steam humidifier - you would be going to the breaker box often when those kick in. Worst of all, you have to remember to plug your cars only just as the last person goes to sleep.

All-electric appliance households have higher rated service as a norm. I've got 200A with gas heating though.
But nevertheless, programmable charging time and current limit solve both problems right now.

 

[ac_power]

I have one HPWC on #6 THNN. Going to add a second on the same circuit. Have a 50a breaker and a separate EV meter. I can charge off peak for $30/mo as long as I stay below 50a.

It's a question of the house service and your combined daily driving in all EVs (and how it changes over time).
If numbers come together, maybe makes sense to run separate branch to guarantee 40..48A per car.

 

[ac_power]

200 amp service (upgraded during my ownership of the house).

How much it was before ?

 

[jerry33]

How much it was before ?

100 amp.

 

[csanders90D]

3b. 90A breaker with safety SW, add 2nd HPWC, 72A load sharing.
All using original #4 wiring. Maximum configuration only 10% lower than yours with #2.

Why do you keep posting this? Are you trying to burn people's houses down?

You can't use #4 wiring for a 90A circuit.

 

[MacGreiner]

I received 4 of them in the past few days so they must be fulfilling the backlog.

Got my black signed one today!

 

[Prunesquallor]

Assuming 11.5 KW charging for 8 hrs with 80% efficiency, max overnight capacity will be ~74 KWh to the battery, split between two cars. Sounds marginal.
snip

It’s enough to charge two Model 3s from 30% to 80%. Every night.

 

[ac_power]

Why do you keep posting this? Are you trying to burn people's houses down?

You can't use #4 wiring for a 90A circuit.

Absolutely not.
But you can use it for 85A circuit behind 90A breaker. 240.4(B).
To be totally correct, continuous current should be limited at 68A of course, but I would keep 72A and sleep well, because it's regulated load, and still way below 75 C rating capacity.

Didn't know it's possible to burn something down by posting at forum.
People who cannot learn / calculate / double-check / measure / do regular inspections, shouldn't be touching this anyway.

 

[tga]

Why do you keep posting this? Are you trying to burn people's houses down?

You can't use #4 wiring for a 90A circuit.

#4 is good for 85A in the 75C column. You are allowed to round up the breaker to the next standard size (90A), but that DOES NOT give you a 90A circuit - the wire is still the weak link and limits you to 85A max, 85A*80%=68A. But there is no 68A setting on the HPWC, so you need to dial it back to 64A (80% of 80A).

You can't use the 90C column (95A for #4), because the terminals on the HPWC are only rated to 75C, and you won't find a (residential) breakers with 90C terminals.

 

[ac_power]

It’s enough to charge two Model 3s from 30% to 80%. Every night.

Yes, but it's pretty much best case today. 2 x MX may start starving already.
Even without future power-hungry cars, the more Tesla penetrates ICE market, the higher will be demand for longer daily mileage..

 

[tga]

Yes, but it's pretty much best case today. 2 x MX may start starving already.
Even without future power-hungry cars, the more Tesla penetrates ICE market, the higher will be demand for longer daily mileage..

You really only need to recharge at night what you use in a day. If you drive 50 miles/day, it doesn't really matter if your range is 200 miles or 2000 miles. Daily charge time is still the same.

 

[ac_power]

You really only need to recharge at night what you use in a day. If you drive 50 miles/day, it doesn't really matter if your range is 200 miles or 2000 miles. Daily charge time is still the same.

50 mi on M3 will be 13 KWh, on MX - 17 KWh, with AC - 20, in freezing temperatures - 25, with comfortable cabin and battery heating - 30. You've got the idea.
And 50 miles is quite shy for daily commute I would say.

 

[csanders90D]

Absolutely not.
But you can use it for 85A circuit behind 90A breaker. 240.4(B).
To be totally correct, continuous current should be limited at 68A of course, but I would keep 72A and sleep well, because it's regulated load, and still way below 75 C rating capacity.

Didn't know it's possible to burn something down by posting at forum.
People who cannot learn / calculate / double-check / measure / do regular inspections, shouldn't be touching this anyway.

Forum posts don't burn things down, but people following your advice might. Just because you're comfortable overloading a circuit, doesn't mean that overloading should be a recommended installation.

The NEC has a certain margin for safety. Running at 72A on a circuit rated for 68A continuous load eats away at that margin. Did you remember to de-rate for those hot Arizona summers? That also lowers the ampacity, further eating into that safety margin. At some point the margin is gone and fires start.

 

[dhrivnak]

I did two 14-50 each on their own circuit. More flexible in case the second car or third is a none Tesla. Such as hybrid plugin.

I did three NEMA 14-50’s pulled off a separate sub panel that I added.

 

[whitex]

Assuming 11.5 KW charging for 8 hrs with 80% efficiency, max overnight capacity will be ~74 KWh to the battery, split between two cars. Sounds marginal.

Very unlikely people will leave and arrive with both Tesla at the same time, both need full charge, and stay at home only 8 hrs. Usually one person arrives earlier, one later, with balancing you get full 48A is there is only once car. Also, most people spend more than 8hrs per day at home - remember, this is not sleep time, the cars charge any time you're at home. Lastly, most days both cars didn't use all their battery charge while out.

 

[ac_power]

Forum posts don't burn things down, but people following your advice might. Just because you're comfortable overloading a circuit, doesn't mean that overloading should be a recommended installation.

The NEC has a certain margin for safety. Running at 72A on a circuit rated for 68A continuous load eats away at that margin. Did you remember to de-rate for those hot Arizona summers? That also lowers the ampacity, further eating into that safety margin. At some point the margin is gone and fires start.

I already said - everyone can do it in the way he is comfortable with. Who's in doubts, will hire an electrician which just follows the code.
I'm not at the point of upgrading to 85A-rated-circuit-with-90A-breaker yet, maybe I will come to the same conclusion, of cutting it down to 64A or even below. This is not the point.
The point is - #4 gives a short term flexibility which #6 doesn't, for minimal difference in price.