Chart of Wiring/Breaker/Conduit for Tesla Wall Connector

I believe that with the correct insulation and other parts, it is possible to use #4 wire for a 90 Amp breaker and 72 Amp charging.

The older HPWC's had settings for 60 Amp and 90 Amp breakers which were some nice cost sweet spots using #6 and #4 copper wire.

Hopefully FlasherZ will give us a definitive answer, but I'll chime in.

Ampacity of copper wire depends on temp rating of the insulation and terminators. See: Ampacity Charts or American wire gauge - Wikipedia, the free encyclopedia

Note: Every amp rating below is a breaker rating for the circuit; charge current will be 20% lower.

Your chart assumes the conservative 60°C ratings for 20-70A and 90A breakers. 4 AWG @ 80A and 3 AWG @ 100A requires moving up to 75°C wire and breakers (vs 70A max and 90A max, respectively @ 60°C)

I haven't found anything that definitively states the temp rating of the terminals in the HPWC, but the installation manual recommends using 75°C 3 AWG wire on a 100A breaker for 80A charge current. This implies the terminals are 75°C rated. If you use 75°C wire and terminations, you can push 8 AWG to 50A, 6 AWG to 70A (rated for 65, round up to next std breaker = 70A), and 4 AWG to 90A (again, 85A, round up).

Note that 2 AWG is the max for the the HPWC terminals, and people have pointed out it's hard to fit it in. Also, 3 AWG is a somewhat oddball size, and may need to be ordered.

Personally, I would follow your recommendations and go by the 60°C wire ratings. The wire will run cooler, and you will get less voltage drop. When sizing wire, bigger is always better. As your second chart shows, the price difference is minimal. Note that this means using 3 AWG for 80A and 2 AWG for 100A.

Edit: Of course I forgot - great post. It's nice to have conduit fill and ground conductor size in one place.

I don't see anything that really sticks out to me, other than what's been pointed out already. There are lots of "it depends" scenarios that aren't covered - for example, temperature derating, etc. For the lower current ratings, NM cable requires 60 degC rating, while wire-in-conduit can use 75 degC; a NEMA 14-50 can be installed on #8 in conduit, but must be on #6 if NM (Romex).

Based on my memory (which could be faulty), I seem to recall that 2AWG wire was less expensive than 3AWG wire. I also seem to recall that I paid about 0.85/foot for 2AWG wire from a supply house I found on the internet.

I agree that 2AWG wire is difficult to work with (compared to the typical wiring found in a residential house).

Also, as noted above, the older HPWCs provided for the hookups between 60A and 90A but not 20A to 40A. The current HPWCs dispense with settings for 60A to 90A hookups and added 20A to 40A hookups.

A question about kW to car. It looks like this column uses a Voltage of 220 Volts. The vast majority of residential service is 240 Volts in the US, and much of the commercial, 3-phase service is 208 Volts. Why did you use 220 Volts; was that a compromise or average of residential and commercial?

I have two HPWC's. One typically starts at 245 Volts at 0 current and sags to 240 Volts under load. The other typically starts at 247 Volts at 0 current and sags to 244 Volts under load. The latter one has a short 12' run of #2 copper from a 400 Amp panel.

220/110 Volt, split-phase service dates to Edison's DC distribution system and is rarely seen today. Mains electricity - Wikipedia, the free encyclopedia

Cottonwood said:

I believe that with the correct insulation and other parts, it is possible to use #4 wire for a 90 Amp breaker and 72 Amp charging.

The older HPWC's had settings for 60 Amp and 90 Amp breakers which were some nice cost sweet spots using #6 and #4 copper wire.

Click to expand...

I have one of those older HPWCs, and it has breaker settings from 40A to 100A in 10A increments (8 settings, with the 8th setting being the test mode). I have a 60A breaker, wired with #6 THHN, charge at 48A, and with dual chargers in the car, achieve ~35 miles of range per hour of charging -- enough to charge a depleted 85kWh battery after midnight.

Danal said:

Good catch. It should be 240 for a home, and 208 for commercial. That would also throw off all the times, etc... although I did not calculate those, I took them from Tesla's site. I wonder how they are making these calculations? We might be able to infer from "back" calculating. Anyway, I have adjusted to 240V, and pointed out in the disclaimers that 208 will be slightly different.

Thanks!

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They have adjusted them over time, too. Originally, they used a 31 miles/hour charged on the 240V/40A column, and that was revised to 29 later.

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tga said:

I haven't found anything that definitively states the temp rating of the terminals in the HPWC, but the installation manual recommends using 75°C 3 AWG wire on a 100A breaker for 80A charge current. This implies the terminals are 75°C rated. If you use 75°C wire and terminations, you can push 8 AWG to 50A, 6 AWG to 70A (rated for 65, round up to next std breaker = 70A), and 4 AWG to 90A (again, 85A, round up).

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Just as a quick clarification point - the conductor must always be sized for load - there is no rounding up. If the limit is 65A, you cannot present a load of 70A. You can use a 70A breaker to protect a 65A load and conductor against overcurrent, but the wire must be sized for the load.

This means you cannot use the 70A HPWC setting on a #6 wire. #4 is required for 70A.

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Danal said:

1) Now specifies THHN wire. Which must be in conduit. If you use something else, EVERYTHING changes, and none of this applies.

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If this is the case, then you're fine with #8 for 50A (your chart lists #6).

Danal said:

Yep, at 90 deg C. Unfortunately, my ability to update the post has expired.


I could throw a technicality on the table and say it is THHN and at 75 deg C... then all would be correct... but that's cheating because THHN is rated to 90C... So, instead, let me say:

Excellent, excellent catch FlasherZ! Thank you very much.

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#8 is rated 50A even at 75 degC. You have to use the 75 deg columns with THHN anyway at the breaker because very few breakers, enclosures, and other termination equipment are rated at 90 degC anyway. And no problem - thanks for putting it together. You can report your own post and ask admins to update it.

I usually tell people #6 anyway because of the tendency to use NM. Few people outside Chicago like the idea of doing anything more than EMT sleeves conduit-wise in homes.

Danal said:

Would changing 50A to #8 (with a #10 ground) also then allow 1/2" conduit?

If so, this could change my (single charger car on order) neighbor's mind about "going ahead with 100A for the future". He might still want to go big... but this change would bring the total 50A vs 100A cost difference to around 25%.

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If you're using 2 #8's and a ground, then yes - it's ok. If you're running a neutral, then no.

FlasherZ said:

Just as a quick clarification point - the conductor must always be sized for load - there is no rounding up. If the limit is 65A, you cannot present a load of 70A. You can use a 70A breaker to protect a 65A load and conductor against overcurrent, but the wire must be sized for the load.

This means you cannot use the 70A HPWC setting on a #6 wire. #4 is required for 70A.

Click to expand...

Thanks for catching that - round up breaker ratings, but not wire ratings.

What did people use for high amperage service disconnect or did you guys not have one?

What about a column for those using NM wiring? I used 2/3 NM for my 100 amp sub panel and used 6/3 for my two 14-50 outlets.

jcaspar said:

What about a column for those using NM wiring? I used 2/3 NM for my 100 amp sub panel and used 6/3 for my two 14-50 outlets.

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NM wiring requires you use the 60 degree column. 2/3 NM is good to 95 amps, and 6/3 is good to 55 amps. Technically, using 2/3 as a feeder to a small subpanel in the garage is improper if it is reasonable that you would use both 14-50's for EV charging at the same time, because the load calcs will require a 100 amp rated conductor. Some inspectors are likely to let it past because they're used to feeders being aggregate for a lot of small loads that can't possibly all run at the same time. For example, if you told the inspector that one 14-50 was for an RV and one 14-50 was for EV charging, you'd pass because it's highly unlikely that the RV's load would exceed the 45A you have left after deducting for the EV charging load.

This should be a sticky and updatable by the OP...

Jeff

ged said:

What did people use for high amperage service disconnect or did you guys not have one?

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In most jurisdictions in the US, it is acceptable to use the breaker as a disconnect if it is within sight of the EVSE. I put one in anyway. I recommend the Hubbell.