pjanisch said:
Hello,
I just want to make sure I am doing this correctly. I purchased Leviton's 32amp, 240volt charging station. With my Dad's help, I am going to install a 40amp double-pole breaker at my service panel, then run 2 hot wires and 1 ground wire out to my garage (about 20 feet). Will I be OK using #10 wires or do I need to use #8? I will be running the 220 wires in 3/4" EMT that already contains a 110 circuit, is that OK?
Your local codes and regulations will have the final say*, but per NEC a 40A breaker is correct for that unit (using the 80% rule), and 10/2 should be fine when considering the distance and voltage drop, also incorporating the 80% rule. Technically the 10/2 is 30A rated, so your local codes may be sticklers, but hopefully common sense prevails here. Here are some tools I often use when doing this.
EDIT: FYI - I re-read the NEC sections related to this and it basically says "your breaker must not exceed the amperage rating for the wire". So in order to use a 40A breaker, you
would need 8/2 per NEC table 310-16 to be NEC compliant. The idea is that you want the breaker to trip before the wire burns up and causes a fire. Which is just nonsense given your short distance, but that's that way it is.
Voltage drop calculator #1
Voltage drop calculator #2
Conduit fill guide
The second calculator lets you select the conduit type, which is important because what you're ultimately mitigating by your choice of wire gauge, wire type, and conduit, is the effect of heat. Heat is the risk, and that is what almost all wiring code is centered around (other than the obvious risk of electrocution). Heat is driven by resistance, which is primarily reflected in the line loss. As long as your line loss is low enough, your ambient temperature is low enough, and your conduit isn't overstuffed with other heat generating wire, your total heat is kept in check.
EDIT: NEC Table 310-19 says you can have up to 6 conductors in the conduit and still be at the 80% rule, so you should be fine there since you'll only have 3 (neutral doesn't count).
FYI - If your 20 foot run is complicated, you might consider running a heavier gauge now to allow an easier upgrade to a higher power EVSE in the future.
If you're at all confused or uncertain, PLEASE consult a qualified electrician. Safety first here. Always.
* I am not an electrician, but I play one on TV.
Off topic, but what is the length of the level 1 charger that comes with the car?
Sorry, don't know that one off the top of my head.
WP
