[ClarityDave]

You both missed my point. An EVSE rated to pass 80 amps at 240 volts cannot be wired into anything less than a 100 amp circuit per NEC standards. It doesn't matter if it's the vehicle or the EVSE that pulls the current, the fact that the EVSE is connected to the circuit and will allow this much current to be pulled through means it is the EVSE that must comply with the circuit restrictions. The J1772 standard is for EVSE/vehicle communications, not wall circuit/vehicle communications.

If that is a rule of the NEC then it’s a dumb one. If I have a car that draws a maximum of 30A and I have an EVSE rated at 80A I should be able to set the EVSE to communicate a maximum charge of 30A and wire it to a 40A circuit. As long as the EVSE does not communicate to the vehicle that it can supply more than the circuit is designed for, you should be just fine. But I assume the NEC rule is to prevent even dumber people from doing something stupid like setting the EVSE to a higher charge rate than what the circuit allows. And in any case, the breaker protects the premises wiring. If you have a 40A breaker and wiring that is rated for 40A you would be adequately protected from a connected EVSE rated at 80A and a vehicle trying to pull that much. The breaker would just trip if the vehicle tried to pull more than 40A.

 

[jzchen]

80A EVSEs are $2k+. Most people won't spend so much on a unit and then connect it to a 40A circuit to draw 32A. Gotta pay an electrician labor and possibly for the commute.

I wonder how much efficiency is gained sending solar energy direct to the DCFC. I like that idea...

 

[ClarityDave]

80A EVSEs are $2k+. Most people won't spend so much on a unit and then connect it to a 40A circuit to draw 32A. Gotta pay an electrician labor and possibly for the commute.

I wonder how much efficiency is gained sending solar energy direct to the DCFC. I like that idea...

My guess would be that you could gain 5-10%.

 

[obermd]

If that is a rule of the NEC then it’s a dumb one. If I have a car that draws a maximum of 30A and I have an EVSE rated at 80A I should be able to set the EVSE to communicate a maximum charge of 30A and wire it to a 40A circuit. As long as the EVSE does not communicate to the vehicle that it can supply more than the circuit is designed for, you should be just fine. But I assume the NEC rule is to prevent even dumber people from doing something stupid like setting the EVSE to a higher charge rate than what the circuit allows. And in any case, the breaker protects the premises wiring. If you have a 40A breaker and wiring that is rated for 40A you would be adequately protected from a connected EVSE rated at 80A and a vehicle trying to pull that much. The breaker would just trip if the vehicle tried to pull more than 40A.

Since the EVSE and car negotiate the power draw from the wall, the EVSE must comply with NEC requirements and not be able to draw (or offer) more than 80% of the circuit's rated current. The problem is there is no communication between the EVSE and the circuit, so the EVSE has no knowledge of how much the circuit can handle; it just assumes it's been installed on a circuit capable of handling the maximum draw the EVSE is capable of.

Finally, do NOT assume a breaker will work fast enough to prevent overheating related issues from an EVSE that's drawing too much power. Yes, they should, but there are enough electrical house fires every year to remind us that home wiring is frequently substandard.

 

[ClarityDave]

Since the EVSE and car negotiate the power draw from the wall, the EVSE must comply with NEC requirements and not be able to draw (or offer) more than 80% of the circuit's rated current. The problem is there is no communication between the EVSE and the circuit, so the EVSE has no knowledge of how much the circuit can handle; it just assumes it's been installed on a circuit capable of handling the maximum draw the EVSE is capable of.

Finally, do NOT assume a breaker will work fast enough to prevent overheating related issues from an EVSE that's drawing too much power. Yes, they should, but there are enough electrical house fires every year to remind us that home wiring is frequently substandard.

The thing is that some EVSEs can be set to offer a certain maximum amperage and therefore could safely be installed on a circuit with a lower ampacity rating than the maximum of the EVSE. For instance, I have a Siemens Versicharge. It is a 30A EVSE. However, I could safely install it on a 20A circuit by opening it up and setting its maximum current delivery to 15A. I could also install it on a 10A or 30A circuit as it has settings for those too (7.5A & 22.5A). I suppose you could come up with some other reasons why the EVSE has such a setting but the most logical one is so that it could be installed on circuits with less than a 40A rating.

That might be why it’s called a “Versi”Charge. However, because of the restrictiveness of the NEC, it’s not so versatile after all.

And of course we don’t assume that a breaker will ever protect any circuit that it’s supposed to protect and any device could be attached which draws too much power.

So in my opinion the code is “dumb” in that it will not allow you to connect an EVSE that is “smart” enough to communicate a lower power limit to the car.

 

[obermd]

The thing is that some EVSEs can be set to offer a certain maximum amperage and therefore could safely be installed on a circuit with a lower ampacity rating than the maximum of the EVSE. For instance, I have a Siemens Versicharge. It is a 30A EVSE. However, I could safely install it on a 20A circuit by opening it up and setting its maximum current delivery to 15A. I could also install it on a 10A or 30A circuit as it has settings for those too (7.5A & 22.5A). I suppose you could come up with some other reasons why the EVSE has such a setting but the most logical one is so that it could be installed on circuits with less than a 40A rating.

That might be why it’s called a “Versi”Charge. However, because of the restrictiveness of the NEC, it’s not so versatile after all.

And of course we don’t assume that a breaker will ever protect any circuit that it’s supposed to protect and any device could be attached which draws too much power.

So in my opinion the code is “dumb” in that it will not allow you to connect an EVSE that is “smart” enough to communicate a lower power limit to the car.

The NEC Code doesn't specify what types of devices can be put on a circuit. It does specify that continuous load, which is what an EVSE creates, can be no more than 80% the circuit's rated load. If the EVSE can be configured to run at a lower maximum amperage then it complies with the 80% requirement. If it doesn't, and many don't, then it doesn't comply. One caveat for variable setting EVSEs, be careful that someone doesn't up the current the EVSE can pass through to the vehicle.

 

[EV Nerd]

The F-150 Lightning will L2 charge at 19.2 KWh. I really think this is a case of how much power do you need to fully recharge the battery in 8 hours. Trucks will need more power than sedans or SUV/CUVs.

Why eight hours? Most people spend at least twelve hours at home between work days.

 

[obermd]

Why eight hours? Most people spend at least twelve hours at home between work days.

Many areas charge extra during peak electric use hours. 8 hours allows you to start charging at 10 PM, which is almost always after peak charge hours, and have a full battery by 6 AM. I've looked at several different EVs for people and it appears the sweet spot for L2 home charging is 8 to 10 hours. Since no one will be getting home with a fully depleted battery, 8 hours works.

 

[EV Nerd]

Many areas charge extra during peak electric use hours. 8 hours allows you to start charging at 10 PM, which is almost always after peak charge hours, and have a full battery by 6 AM. I've looked at several different EVs for people and it appears the sweet spot for L2 home charging is 8 to 10 hours. Since no one will be getting home with a fully depleted battery, 8 hours works.

Makes sense. Thanks.

 

[ClarityDave]

Many areas charge extra during peak electric use hours. 8 hours allows you to start charging at 10 PM, which is almost always after peak charge hours, and have a full battery by 6 AM. I've looked at several different EVs for people and it appears the sweet spot for L2 home charging is 8 to 10 hours. Since no one will be getting home with a fully depleted battery, 8 hours works.

Of course it’s unlikely most people will need to charge it for even that long. My Clarity takes maybe 2.5 hrs to fully charge but I normally don’t even use that much in a day. This is why I think the J1772 connector is here to stay for awhile. It’s all that most people need.

 

[obermd]

Of course it’s unlikely most people will need to charge it for even that long. My Clarity takes maybe 2.5 hrs to fully charge but I normally don’t even use that much in a day. This is why I think the J1772 connector is here to stay for awhile. It’s all that most people need.

The J1772 connector is definitely here to stay as it's the common (except Tesla) connector and protocol (including Tesla) for all AC charging.

For your other comment, PHEVs don't have that large of a battery so a 20 amp circuit is more than sufficient to charge. The chart below shows how many KW can be supplied the vehicle in 8, 10, and 12 hours. The chart covers all voltages and currents covered under the J1772 standard. The * hours columns assume a 10% charging loss to heat. If you notice, when you get to 12 hours even a 120 volt 15 amp circuit is sufficient, meaning no PHEV needs a 240 volt circuit. When looking at a full BEV, the battery capacity will be listed in KWh - this directly relates to the numbers in the 8, 10, and 12 hour columns.

Voltage	Circuit Amps	NEC Max Charging Amps	KW per hour (KWh)	8 hours	10 hours	12 hours
120	15	8	0.96​	6.9	8.6	10.4
120	15	12	1.44​	10.4	13.0	15.6
240	20	16	3.84​	27.6	34.6	41.5
240	30	24	5.76​	41.5	51.8	62.2
240	40	32	7.68​	55.3	69.1	82.9
240	50	40	9.6​	69.1	86.4	103.7
240	60	48	11.52​	82.9	103.7	124.4
240	70	56	13.44​	96.8	121.0	145.2
240	80	64	15.36​	110.6	138.2	165.9
240	90	72	17.28​	124.4	155.5	186.6
240	100	80	19.2​	138.2	172.8	207.4