What current capacity does 6 AWG AL TYPE SE have for an EV charger?

Question

We recently finished our basement and had electrician run a cable to the garage for an electric vehicle charger that terminates in a junction box in the garage. From the 200A panel the cable is connected to a 2-pole 40A breaker and connected to cable with the markings "APAR INDUSTRIES LTD 3 CDRS 6 AWG+ 1 CRD 6 AWG AA-8000 AL TYPE SE STYLE R 600V SUN-RES (UL) E498924 2022 10856 FT".

I'd like to purchase a charger with the most power this setup could support. Can the cable support a 40A charger with a change to a 50A breaker? Can it support more? Am I stuck with 40A breaker? In a perfect world I'd like a 48A charger. Any other options? Thank you!

Answer 1

6 AWG aluminum SE is good for 50A based on this ampacity table

That is enough for 40A continuous. EV charging is the epitome of a continuous load (it doesn't even cycle like HVAC or an oven will once they reach the target temperature).

40A is enough for roughly 29 - 37 added miles of range per hour of charging, based on this Tesla Wall Connector table. Your actual mileage will vary, but basically that is more than enough to charge a relatively "empty" (10% - 20% battery charge) EV overnight. Hardly anyone needs more than that on a regular basis.

A couple of other notes:

• Do NOT use a receptacle. That is crazy in general and especially at higher charge rates. Use a Tesla Wall Connector or similar device hardwired.
• The Tesla Wall Connector, and likely many other EVSE devices, can't handle aluminum wire directly. So you need something in between. You may also need a local (i.e., within sight) disconnect) though that varies. The simple solution to both problems is a disconnect box, such as a 60A "air conditioner" disconnect. Just make sure it can handle both aluminum and copper and that it is truly up to the task. One I just looked at says 60A but also says 7.2kW, which would only be 30A.

Answer 2

You have to start with your service load calculation.

Everybody forgets this one lol.

This is a standard form based on NEC Article 220 which determines the ampacity required for your loads, and therefore, the amount of charging you are able to handle.

"I need MAX possible charging" is what newbies say

Welcome to EVing - I say unabashedly. But still, you don't need to walk right into well-known newbie errors. Particularly the error of burdening a service with a load it can't handle.

In fact I can think of two EVangelists on Youtube - Technology Connections and Out of Spec Reviews - who have empty 50A sockets because they use smaller charge rates. They just don't need 50A, and these guys drive a lot! Here's one laying out the facts. I've cued it up to 28:15.

https://www.youtube.com/watch?v=Iyp_X3mwE1w&t=1695s

Think about how you would fuel your gas car if you had a sympathetic neighbor who owned a gas station, and every day brought you 5 gallons (no more) of gas and poured it in your tank. You'd exploit that to the max, right? Only pay retail for gas when you outrange your supply. That's life on a 15-20A (240V) charging circuit.

If your service can support it, sure, why not. But calling it a "must-have" is dumb. If you drive 40 miles your car does not need to finish recharging in an hour. You have all night.

"But I gotta have it. I might get an electric MRAP!"

And your service load calculation can handle it? Well, okay. The #6 aluminum SER is rated for 50 amps. It can go directly to a NEMA 14-50 socket that is rated for 75C thermal and for aluminum wire (which is most). It can also go to a 6-50 socket as EVs don't use neutral, but since you have the neutral anyway, might as well install the 14-50 and be able to support a large RV.

There's nothing wrong with aluminum wire at these large sizes. The electrician used fine wire, just with one snag for direct wiring.

You can just cord-and-plug connect the EVSE at that point if it is approved for cord-and-plug. Otherwise, bad news - no major EVSE has terminals rated 75C or for aluminum wire, for some reason. So you will need a splice method to go to copper - either #8 copper THHN inside conduit, or #6 NM-B or UF-B type cable.

As manassehkatz observes, the cheapest 3-wire AL-CU splice in town is a disconnect.

If you are DIYing this stuff, you should use a torque tool to set screw torques to spec. That's a NEC requirement, 110.14.