HPWC on 60amp #6?

[eprosenx]

If your jurisdiction is on 2017 NEC, you should be able to use 6-6-6 copper or 4-4-6 AL type SE (including SER or SEU, I believe, but not type USE) cable.

Under 2017 code you are not required to derate this cable type to 60C so long as the conductors are 8 AWG or larger. This will get you significantly more ampacity than Romex (NM-B) without going to conduit. Certainly enough to charge at 48A.

The Lowe's site has 6-6-6 Cu for $2.24 a foot. But the 4-4-6 AL is a particularly good deal - $0.67/foot at wireandcableyourway.com.

Good callout on the SE cable! I have thought about this a lot in the past (trying to figure out what to do for my new house to support up to 100 amps in a pre wire situation). You are allowed to use SW cable at the 75c rating rather than 60c that NM cable is limited to, so that makes a huge difference.

The annoying part is that I have not been able to find any 3 AWG copper with just two hot conductors plus ground in SE wire. It is typically used for feeders to subpanels and so it generally always has a neutral. Also, it most commonly is used with aluminum wire not copper.

Now the big warning: DO NOT use aluminum wire into the Wall Connector. It is not rated for use with aluminum.

So with these factors at play, I have not found SE cable to recommend for wall connectors at 100a. Though now I am wondering if anyone makes 6awg SE wire with just two hots and a ground in copper?

 

[tls]

You can use a J box and connectors like https://www.amazon.com/dp/B005FMQ5BQ to transition from Al to Cu wire right before the Wall Connector. That's what I'd do. You could also use much cheaper uninsulated split-bolt or splicer-reducer connectors available almost anywhere but though these are OK per code inspectors may not like to encounter them with the tape already on (and you'll need a bottle of noalox, and... really, I'd spend for the nicer splices).

It's a lot more expensive, but Lowe's has what you're looking for in copper, albeit with an oversized ground: https://m.lowes.com/pd/Southwire-6-6-6-Copper-SEU-Service-Entrance-Cable-By-the-Foot/3129323 . Not sure why it's made that way. Can't find 6-6-8 copper SE cable in anything but 500 foot reels, unfortunately. I'd go with the Al cable and short copper pigtails into the HPWC.

 

[eprosenx]

You can use a J box and connectors like https://www.amazon.com/dp/B005FMQ5BQ to transition from Al to Cu wire right before the Wall Connector. That's what I'd do. You could also use much cheaper uninsulated split-bolt or splicer-reducer connectors available almost anywhere but though these are OK per code inspectors may not like to encounter them with the tape already on (and you'll need a bottle of noalox, and... really, I'd spend for the nicer splices).

It's a lot more expensive, but Lowe's has what you're looking for in copper, albeit with an oversized ground: https://m.lowes.com/pd/Southwire-6-6-6-Copper-SEU-Service-Entrance-Cable-By-the-Foot/3129323 . Not sure why it's made that way. Can't find 6-6-8 copper SE cable in anything but 500 foot reels, unfortunately. I'd go with the Al cable and short copper pigtails into the HPWC.

Yeah, I have thought about transitioning like that in a junction box right before the Wall Connector as well. Aluminum is just so much crazy cheaper and more available (and less stiff). But I worry if others who come later may not realize that the circuit is not one continuous conductor rating throughout. Seems like an anti-pattern if not outright banned by NEC (but I have not read anything to this effect). You would have to go with the lower rating of the two cable types/sizes.

So I had not seen that 6-6-6 wire before. That is a really massively oversized ground. I wonder if that is a byproduct based on the fact that SEU has the ground wrapped around the cable and so you would end up with too few strands if it was less than 6 awg?

Really you want SER not SEU for the Wall Connector. Dealing with all those braids and shoving them under the ground terminal seems like it would be a royal pain. I don't think they seem to actually make that in SER, I only see it as SEU. FWIW, you only need 10awg copper per code for up to a 60a circuit. I wish they made 6-6-10 SER Copper wire. 6-6-8 would be fine as well, but again, I want SER not SEU. I also want 3-3-8 or 3-3-6 in SER.

P.S. It is totally stupid that the larger gauge NM-B cable is not allowed to use the 70c terminal sizing. My understanding is that NM-B and SE cable are basically the same stuff wire and insulation wise. The NM-B restriction to 60c was based on some fires with small gauge NM cable in an attic with insulation that was way too hot (if what I was told is true). I don't see how it is applicable to larger (8awg and up) circuits. Also, most new lights are LED anyway so the issue may be moot anyway. Silly to allow SE cable but not NM cable to be used at 70c.

 

[SSedan]

So my opinion on why Tesla says no aluminum is that cable tends to heat up when used towards the upper end of capacity for long periods. Aluminum expands more with heat than copper, this is known to create loose connections over time.

Aluminum is fine for service cable because the entire service is unlikely to me near max capacity long enough or often enough to create a lot of heating/expansion cycles. An EV charging circuit most definitely will.

Copper pigtails just means another joint in the line another place to build heat and loosen a connection, not to mention the split bolt connectors and extra junction box you have to buy eating into savings of using the wrong wire........

 

[Feathermerchan]

Another interesting point: Utilities use 1/0 Al for 200A services. NEC rates it at only 120 to 135A . Utilities are not governed by NEC but by NESC.

 

[tls]

So my opinion on why Tesla says no aluminum

This didn't sound like what I remembered, so I looked. The terminals on my HPWC are marked (in very very small lettering) CO/ALR. This matches what I found by Googling. Was this changed for the second-generation HPWC units?

A properly torqued and lubricated compression connection will not pose a safety issue, which is why it's allowed by code. Even in the small wire made from, um, "legacy" Al alloys so disastrously used in homes in the 1970s, this is precisely how they're made safe with Alumiconn connectors -- the Alumiconns are teensy tiny versions of the screw fittings used for splicing large wire for many years.

If your jurisdiction is picky and requires an outdoor locking disconnect for the HPWC rather than just a locking breaker (per 625.23 because it's "rated greater than 60 amps") you can just use the terminals of the disconnect for the transition - no added expense at all.

All that said, unless you're going more than 50 feet or so from the panel the cost of using the 6 gauge copper will be under $100 so why not. Point really is, there is multiconductor cable, rated for indoor use (type SE), which you can use for >40A charging loads.

 

[eprosenx]

This didn't sound like what I remembered, so I looked. The terminals on my HPWC are marked (in very very small lettering) CO/ALR. This matches what I found by Googling. Was this changed for the second-generation HPWC units?

A properly torqued and lubricated compression connection will not pose a safety issue, which is why it's allowed by code. Even in the small wire made from, um, "legacy" Al alloys so disastrously used in homes in the 1970s, this is precisely how they're made safe with Alumiconn connectors -- the Alumiconns are teensy tiny versions of the screw fittings used for splicing large wire for many years.

If your jurisdiction is picky and requires an outdoor locking disconnect for the HPWC rather than just a locking breaker (per 625.23 because it's "rated greater than 60 amps") you can just use the terminals of the disconnect for the transition - no added expense at all.

All that said, unless you're going more than 50 feet or so from the panel the cost of using the 6 gauge copper will be under $100 so why not. Point really is, there is multiconductor cable, rated for indoor use (type SE), which you can use for >40A charging loads.

I don’t have the link handy on my phone, but I am very sure the second gen Wall Connector instructions say no aluminum.

I agree that it is likely just a matter of Tesla wanting to add another margin of safety. Aluminum oxidizes and can make poor connections if you don’t follow a specific procedure while terminating it (involving the anti oxidation goop), and as mentioned, it expands and contracts more thermally which can lead to terminal connections loosening.

As others mentioned, EVSE’s will take the wire directly to max capacity and then back to no load on every single charging cycle where as most of the other uses (service entrance, feeder, range/oven) don’t require so frequent and dramatic load changes.

I am really debating what to put in my future house. There is no one obvious solution. I may just run 1” conduit and future proof myself.

 

[tls]

I don’t have the link handy on my phone, but I am very sure the second gen Wall Connector instructions say no aluminum.

I agree that it is likely just a matter of Tesla wanting to add another margin of safety. Aluminum oxidizes and can make poor connections if you don’t follow a specific procedure while terminating it (involving the anti oxidation goop), and as mentioned, it expands and contracts more thermally which can lead to terminal connections loosening.

As others mentioned, EVSE’s will take the wire directly to max capacity and then back to no load on every single charging cycle where as most of the other uses (service entrance, feeder, range/oven) don’t require so frequent and dramatic load changes.

I am really debating what to put in my future house. There is no one obvious solution. I may just run 1” conduit and future proof myself.

The one thing I'd recommend against is the perennial "oh, don't worry, a 40A circuit is all you'll ever need, you can just charge overnight". Sometimes I really do want to put on a bunch of charge in a (relative) hurry, say while I'm packing for an unexpected trip. At those times, the 40A charge rate of the Gen1 UMC can be frustrating, but the 24A I get from the ChargePoint unit near one of my common overnight destinations is...infuriating. Especially in the winter when you're siphoning off current to heat the battery. Take the trouble to set yourself up for 40A or 48A charging -- sooner or later you'll be glad you did.

We had an 80A HPWC (100A circuit) at our old weekend place and it did get used. Even just if it was "oh, man, the car didn't start scheduled charging" it is nice to be able to catch up. On the other hand, that installation was a serious pain (not least because the HPWC housing is not well designed to mate to conduit of the sizes that make pulling large copper convenient -- the only style of install that I personally think works well in this application is directly to a post, box, or raceway such that there is no conduit adapter fitting required) and we didn't use rates above 40A particularly often. But for sure I wouldn't limit myself to a 30A or 40A circult (24A or 32A charging, respectively).

 

[tls]

I don’t have the link handy on my phone, but I am very sure the second gen Wall Connector instructions say no aluminum.

So, as it happens I have two shiny (OK, they're not so shiny, less shiny than the Gen1 units actually) new gen2 HPWCs sitting in my basement right now waiting to be installed.

I cannot find any prohibition of aluminum in the installation instructions. On page 18, I do see:

For 80A operation, use 3AWG 167F (75C) rated copper wire or follow local regulations.

However, I read this as a warning against running 80A over the much more readily available #4 copper, or against trying to use #2 aluminum wire which as far as I can tell, won't fit into the terminals on the HPWC, not even the ones in the back extension.

Am I missing something else relevant?

 

[Petrlol]

Page 7: https://www.tesla.com/sites/default...nstallation_manual_80A_en_US.pdf?201612081439

Use only copper conductors.

 

[eprosenx]

So, as it happens I have two shiny (OK, they're not so shiny, less shiny than the Gen1 units actually) new gen2 HPWCs sitting in my basement right now waiting to be installed.

I cannot find any prohibition of aluminum in the installation instructions. On page 18, I do see:

However, I read this as a warning against running 80A over the much more readily available #4 copper, or against trying to use #2 aluminum wire which as far as I can tell, won't fit into the terminals on the HPWC, not even the ones in the back extension.

Am I missing something else relevant?

Page 7 under "Minimum Requirements". Yeah, kind of a weird place for it.

The Charging Installation Tesla folks have told me that #2 (copper) can be accepted in the Wall Connector (that is the max wire gauge), but I think you have to use the back entry extender thing.