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I am installing a EV charger for my car in my garage and I've been all over the internet with a dozen different calculators and they all give different results for what AWG i need to use for my install. some say 1 AWG and some say 6 AWG, I'm pretty sure i need to use 3 AWG but want to verify.

The charger will be on a 100A breaker drawing 80A continuous at 240V and it will be 30ft from breaker to charger, 2 hot and a ground, NO neutral line required, and it will be run inside a 1 inch schedule 40 conduit. Also please correct me if I'm wrong but the ground line can be smaller than the feed lines like if i use 3 AWG for the hot i can use 4 AWG for the ground.

And yes i need the 19kW charge speed, because sometimes i will need to arrive home with like 10% and need to do a turn and burn. at 19kW i will gain about 18kWh every hour at that speed so after 2hr i could be up to 30-40% which is enough to get to a DC fast charger along the road to my next stop. Also yes if i am just plugging in for the night i can adjust the charge speed down in the car to 40A for a more standard overnight charge. But i need the ability to have up to the full 19kW the car can pull from the wall on AC. Besides the charger is only $400 and i bought it a couple years ago for when i finally bought a house.

rasmukri
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    At least you do have a use need for a large charger, most people don't. Really you still need to do a load calculation for you house to see how power you can spare. It does not matter that you need the 100 amps, it is if you have the extra 100 amps to spare from your panel. – crip659 Nov 18 '23 at 15:33
  • Am I to understand you have an all-gas house with 1 large electric appliance on a 40a breaker, and 200A service? Yeah the Load Calc does need to be revisited but unless you have more than 3 kitchen countertop circuits, or a >3000sf mansion, you're probably fine. – Harper - Reinstate Monica Nov 19 '23 at 19:00
  • yeah i got outlets freaking everywhere but most will not be used much and ill not be anywhere near hitting max. – rasmukri Nov 19 '23 at 23:08

3 Answers3

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An 80A ordinary device on a 100A breaker calls for #3 copper (assuming THWN in conduit) or #1 aluminum per a standard wire ampacity chart.

nobody
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STOP! DO NOT DO THIS WITHOUT A LOAD CALCULATION!

Wire size is easy to figure out from an ampacity chart. For individual wires in conduit use the 75 C columns. Check your charger specs as to whether you can use aluminum or have to use copper. That's the easy part.

But you MUST do a Load Calculation. Typical service is 200A. If you have smaller service then you almost certainly can NOT allocate 100A (80A continuous) to EV charging. Even if you have 200A, how much is available will vary depending on:

  • The size of your house
  • Electric vs. gas appliances (water heater, clothes dryer, oven, cooktop, etc.)
  • Other large fixed loads
  • Type and size of HVAC equipment

Putting all these together into one number is done using a Load Calculation. You then subtract that number from your service size to determine how much is available for EV charging. If that's 100A, great. If it is less then you either provision a smaller maximum charge rate (which you don't want to do, but for most people 30A or even 20A is enough) or you need to look into automatic load shedding options - e.g., water heater is turned off when EV is charging. It has to be automatic or it is no good, because otherwise you'll decide to charge at full rate on Thanksgiving Day when induction cooktop and electric oven are running and clothes drying in the electric dryer and it is cold so the HVAC is running full blast. Most of the time it won't be an issue, but when it is an issue it is very serious.

manassehkatz-Moving 2 Codidact
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    yeah its all good I'm 90%on gas for everything anyway the AC is the only appliance that has any power draw and that only draws like 40A or some crap i'll double check how much it draws but its all good with the load on the main panel. – rasmukri Nov 19 '23 at 01:23
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Being over 60A, your charge station requires a disconnect switch. I don't make the rules, but this will save its cost on wire, because a disconnect is a cheap way to splice from aluminum to copper wire.

The textbook answer is #1 aluminum from panel to disconnect, and #3 copper from disconnect to EVSE. ("charger"). Source: Table 310.15(B)(16).

If anyone told you #4 copper or #2 aluminum, they should be barred from giving any further EV advice. They pulled that out of Table 310.12 which is for entire service to a dwelling, and relies on the "load diversity" that a dwelling normally has. (not everything is maxed out at once). Using them for an EV station would be a disaster, because an EV station is the exact opposite of a dwelling - a hard continuous load pegged right at wire rating.

Now, over on Reddit and other EV forums, we see a lot of meltdowns. Boy howdy! The triggering event of these meltdowns is that the terminals are running at their thermal limits already merely by the continuous load right at thermal max rating. And then, a flaw or blemish creates a hotspot, which oxidizes, making it worse, causing a vicious cycle of destruction.

Therefore -- especially because aluminum wire is CHEAP -- I recommend bumping 2 numerical wire sizes, to 2/0 aluminum and #1 copper, or whatever the largest wire the terminals on both ends will accept. (this may be a limitation at the 100A breaker or EVSE). This will keep things significantly cooler, and very significantly reduce the risk of meltdowns.

Note that quality of work is absolutely essential, and you MUST use torque wrenches on all terminals per instructions and per NEC 110.14. "Gud-n-Tite" is scientifically proven to be unreliable.

Harper - Reinstate Monica
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