Outlet and EVSE recommendations for a 30A max circuit?

Congrats!!

Most EVSE are either 16A or 32A. 24A is harder to find, but I did spot this one on Amazon.

It has a NEMA 14-50 plug and you'll need a 50A circuit to be legal with it since it's capable of pulling 40A even if you do have it set to 16A max which is all the Prime can take.

I just use a $190 Duosaida with my 14-30R receptacle.

 

I'm not sure there is any problem with installing a 40A EVSE on a smaller circuit. The current available to the EVSE will be limited by the size of the circuit-breaker protecting it. The EVSE will "advertise" that it can make 40A available to any vehicle plugged into it, but would not be able to deliver that if the vehicle demanded more current than the circuit-breaker permits. This would be a problem on vehicles which want to draw as much current as the EVSE advertises.

However, the Prius Prime will never ask for more than 16 amps, so there would not be a problem unless you get a vehicle with a bigger appetite.

All that being said, you have a different issue with your 208-volt panel. 208-volts is typical of a three-phase supply and, while you can wire your EVSE across one phase of the three-phase circuit (and add a protective ground), I'm not sure how the Prime and the EVSE will respond to 208 volts versus the typical 220- to 240-volt service.

I the best case, it will just slow the charging time by about 10% (2 hrs 30 min rather than 2 hrs 15 min), but it's also possible that your EVSE may interpret the 208-volts as a problem (like a brown-out) and disconnect, thinking it is a fault.

Maybe someone more familiar with available EVSEs and using a single phase of a three-phase panel could speak to this.

(I understand that some ChargePoint station in commercial settings deliver 208-volts because they are wired to one phase of a three-phase system. I also know that there are EVSEs made specifically for use with 3-phase circuits but these are expensive and designed for high-demand applications such as charging large commercial vehicles such as electric buses.)

 

If I were asked to evaluate such an installation (EVSE rated at 40 A connected to a 30 A branch circuit), I’d be inclined to reject it as noncompliant with the National Electrical Code (NFPA 70-2020). EVSE must be listed (625.5), and listed equipment must be “installed and used in accordance with any instructions included in the listing or labeling” (110.3(B)), including the branch circuit size and connection method. In addition, “Overcurrent protection for feeders and branch circuits supplying EVSE [ . . . ] shall be sized for continuous duty and shall have a rating of not less than 125 percent of the maximum load of the equipment” (625.41).

At least in the photos I’ve seen, the label on Prius Prime cars says, “CHARGING CONNECTOR FOR ON-BOARD BATTERY CHARGER, 100V-240V 1ϕ 20A,” which would seem to include 208 V.

EVSE suitable for use at 208 V would also be needed. The ClipperCreek LCS series (for example) can operate at 208 V, but as stated on pages 18–19 and 31 of the manual (PDF), this is allowed only when connected line-to-line in a Y-connected system, not from the high leg in a Δ-connected system.

 

Before you forge ahead with the project, assess your situation and evaluate your need to have an L2 EVSE. Do you really need to complete the full charge in ~2hours? How often does that need arise? Generally speaking, if you are driving only once a day regularly, then overnight L1 EVSE charging covers almost all the charging needs.

 

Thanks. I thought about looking it up, but it was pretty obvious to me that the "spirit of the code" is that wires have to be able to supply the maximum current the outlet (or hard wired device) can demand and the fuse has to be able to protect the wires.

It would be easy for someone to plug in a car that demands more current and alter the max current of the EVSE to charge faster. That would trip the breaker, of course, but then anyone who doesn't know better can still change the breaker w/o upgrading the wiring.

 

This is NOT correct. The EVSE has no way to know the size of your circuit breaker. The EVSE is relying on a proper installation with respect to the size of wires and the circuit breaker capacity. If whatever load you put on a circuit exceeds the breaker capacity based on the amount of overload and the time duration, it will just trip off. The circuit breakers have no communication capability...they just sense overheating.

To be compliant with the electrical code a device can only require a continuous amperage of 80% of the rated capacity of the wires and the breaker.

I am not an electrician, but this is all my best understanding.

Mike

 

To the best of my knowledge, 208v always means 3 phase. No single EVSE can use 3 phase. I do not think any Level 2 EVSE works on 208 volts. The best advise I can give you is "Get a local electrician and listen to them."

208 Volts Is a Weird Voltage. Where Did It Come From? | Thermal Corporation

Googling, both Volt and Leaf owners report that using one phase of a 208 v line is faster than 120 v and slower than 240v.

 

Most equipment that I've seen that runs on 240V says, "208/240."

We had three phase 208 at our radio station in Honduras. Our mini split air conditioners all ran on that as did our two whole house package unit air conditioners and, of course, water heaters had no issue with it. The only problem was the most of the time, the 208 was more like 180-190. They did not like that at all, so we had line conditioners on all the air conditioners. We also had line conditioners on the refrigerators. Even our 120V gas drier needed a line conditioner because the voltage would go too low to open the gas valve.

But that's a quality problem with the electric utility. Basically, if it runs on 240, it'll probably run on 208, just a little less efficiently.

 

I think we're saying the same thing. Regardless of the rated size of the EVSE, the EVSE cannot deliver more than the rating of the circuit breaker. Even when connected to a 30 amp circuit, the electronics in the EVSE will tell the vehicle, "I am a 40-amp EVSE" but if the vehicle accepts that information and attempts to draw more than 30 amps, the circuit breaker will trip.

As I wrote:

And, as you correctly note:

This this true, but if, for example, you install an outlet and you plug in a device, the outlet has no way of knowing what you're plugged in. So, say you plug in an EVSE capable of handling 40 amps but connect it to your Prius Prime which will not draw more than 16 amps, there's no issue.

If you connect a vehicle which draws more current than the circuit-breaker rating, regardless of the rated size of the EVSE, the breaker will trip (as it should!)

If your EVSE is hard-wired, both the code and good practice would require it be served by an appropriately sized circuit and circuit-breaker.

 

Not exactly.

If such a setup was inspected it would be considered out of code. Someone could buy your house and have an EV that draws more current than the Prime and the breaker would trip every time they tried to charge. Having the breaker trip is only a last resort safety measure, primarily intended to detect faulty equipment, faulty wiring as well as when someone plugs in too many devices.

Mike

 

Well, maybe partly the same. You would need to install the right sized breaker and wires for the max current of anything that was hard wired, per the code that @Elektroingenieur kindly looked up and shared. But in the case of a receptacle, you would size the wires for the receptacle and the breaker to protect the wires. So, if the thing you wanted to plug into that receptacle was made to be able to draw more current than the rating of the receptacle, the plug would be different, making it impossible to plug it in to that receptacle.

Good thinking. Yes, 208 and 240 are both two hot legs. 240 is both sides of a split phase supply while 208 is two legs off of a three phase supply with neutral. Each phase is 120 from neutral, but only 208 from each other. I don't think the EVSE is affected by 208 vs 240. Not having the 208-240 voltage on the label is probably just an oversight since 208 is so rare in residential power. The only thing the 208 might affect is the charger itself, which is in the car. Apparently they are also indifferent to the 208v240 question since the articles I've seen on home charging all refer to level 2 charging as 208-240. The only difference is that 208 won't be quite as fast as 240.

Here's a helpful article for people just getting started. How to Choose the Right Home Charging Station? | ChargeHub

 

Good news!

BTW, it should not be necessary to limit the max current of the JuiceBox unless you plan to plug in cars that will draw more than a Prius Prime.