I am thinking of installing a 40 amp direct wire car charger

Question

I want to direct wire a 40 amp car charger. I plan on using a 50 amp breaker. The charger will only be a few feet from the subpanel. I will use #6 wire. Is there anything else to consider when installing the charger?

Answer 1

The starting point here is a service load calculation, as KMJ mentions in a comment. Your meter and service equipment is not a magical "panel of requirement" as per Harry Potter, and it can be overloaded, leading to great destruction and insurance problems. There are two ways to avoid overload: one is to set charge rate to what the panel can spare, the other is EVEMS and we'll get to that.

Local authorities typically want to see NEC 220.82 used for EV installations, with the EV treated as a 100% or 125% load. NEC doesn't include a form, but many municipalities make a form for it; and this one is correct to NEC.

Note line 2 applies to kitchen small appliance branch receptacle circuits only (ones you'd reasonably plug a coffee maker into; not ones dedicated to a built-in appliance e.g. microwave, dishwasher or disposal). Line 3 includes the washing machine and gas dryer. Line 1 covers all other non-installed plug-in appliances.

If there's room in the Load Calculation...

Then I encourage you to watch Technology Connections' excellent video on home charging (28:15-36:00 gets sharply to the point), and with that wisdom applied, consider your charging needs.

If there is a happy match between Load Calc headroom and your lifestyle, you can simply adjust the station's charging rate to conform to that happy point. How do you do that?

On a "wall unit" such as Wallbox, Chargepoint Home Flex, or Tesla Wall Connector, you read the instructions and it will show you a rotary switch, DIP switch or special setting behind an installer's password.

A few units don't allow this (Enphase; ChargePoint non-flex) but just send that unit back; that was forgiveable in 2013 but not now.

Code says that can only be tampered with by "qualified persons", but if you read and understood the instructions, you are one. Ironically, the electrician isn't, nor is the insector, so NEC 625.42 requires you put a durable label near the equipment nameplate saying you changed the setting and to what. The electrician must install the circuit that the nameplate (as modified by that durable label) tells him to.

Since these answers are widely read and linked to, I'll cover travel units. Skip to the next major section if uninterested.

On a mobile/travel unit, you're installing a socket (and costly GFCI breaker if subject to NEC 2020+ or NEC 2017 as amended). We don't love this option due to that cost, and the general inconvenience of such units, and the additional failure points of a socket connection. If the unit offers exchangable adapter/dongle plugs such as Tesla's Mobile Connector, you get a dongle of the correct circuit amps (xx-50 outlets serve as 40A outlets since no 40A sockets exist).

If the unit does not offer exchangable plugs, or the choice is too limited, then you need to switch to a different model of mobile unit which does. Since Tesla has NACS completely covered, and circuits work quite differently outside North America, I'll assume we're dealing with the J1772 "Fetch" connector. For instance, the DeWalt mobile kit features the NEMA 6-20, which as Technology Connections discusses at 32:55 serves the needs of almost everyone.

30 amps is an ungainly size, because the ideal socket, NEMA 6-30, is not well supported. There's better support for the NEMA 14-30 but EVs can't use neutral. Ironically, the "prohibited since 1965" ungrounded NEMA 10-30 is better supported than either of the other ones, even though EVs do need ground (they are misusing neutral, bad for a lot of reasons; worst case you can get a hot skin on your EV!) My best advice is to nudge you toward a hardwired wall unit.

If there isn't room in the Load Calculation for your needs...

In that case we switch gears and go over to an EVEMS system. There's a whole separate article on that here; I won't repeat it.

EVEMS is not what some manufacturers claim it is; see link.