Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Trying to reuse the existing wiring for HPWC. A sanity check for me, please?

This site may earn commission on affiliate links.
Hi all,

I have a disused "Three conductor" (neutral and two hots) 4 AWG SEU AL XHHW wire from the previous HVAC condenser unit routed towards the area where I’d like to locate the Tesla wall charging unit (about a 30ft run). The existing wire is rated at 75 amps / 90 deg C, which gives me some overhead per my understanding. It runs freely along the rim joist, and enters the 1.25 EMT conduit on the descending segment along the concrete wall.

My plan is to put this wire on a 60 amps circuit breaker in the main panel. On another end, I will terminate with a non-fusible 240v switch, which will then feed a HPWC with a short ~3 ft run of copper 6 AWG THHN (x2) / bare (x1) wires in the ¾ inch EMT conduit.

Schematic view:

HPWC Schema.JPG


No electrician would agree to this job as they'd rather run a new 4/3 Romex, but let's just say I'd like to reduce the waste and learn new skills along the way. Since this AL wire is already in the Main Cabinet, I feel that this is really within my capabilities.

Does this seem like a workable solution that will survive the inspection?
Is terminating with a switch (AL to copper) a good idea or I should rather do a subpanel?
Or shall I abandon this and go find other things to do?
 
I would avoid the switch. There are simple/cheap junctions you can use and just put it in a junction box. Look for “Al/Cu wire connectors”, and get the ones that screw down, not the fancy wire nuts. Use corrosion inhibitor (Noalox) on the aluminum connections. As long as the junctions are in a box and the wires are either in conduit or in a wall, it should pass inspection.
 
I would avoid the switch. There are simple/cheap junctions you can use and just put it in a junction box. Look for “Al/Cu wire connectors”, and get the ones that screw down, not the fancy wire nuts. Use corrosion inhibitor (Noalox) on the aluminum connections. As long as the junctions are in a box and the wires are either in conduit or in a wall, it should pass inspection.

Thank you!! That simplifies things a bit. Are you referring to this type of connector?

(Point taken re 100 amps)
 
I would avoid the switch.

The switch is a good idea and will be necessary if you later upgrade.
  • NEC 625.43 Disconnecting Means. For equipment rated more than 60 amperes or more than 150 volts to ground, the disconnecting means shall be provided and installed in a readily accessible location. The disconnecting means shall be lockable open in accordance with 110.25.
 
By the way, a small subpanel may be about the same price as a switch and give you greater flexibility in the future. I used a subpanel with an device that allows the breaker to be locked in the off position to satisfy the lockable open disconnect requirement.
 
  • Like
Reactions: Rocky_H
By the way, a small subpanel may be about the same price as a switch and give you greater flexibility in the future. I used a subpanel with an device that allows the breaker to be locked in the off position to satisfy the lockable open disconnect requirement.

Thank you! I was thinking subpanel in case I’d expand by adding a second HPWC in the future. In this instance I assume the same AL feeding wire will still suffice since HPWC can do power sharing and all I’ll need is to add a second circuit breaker / wire, correct?
 
As long as you ensure that the two wall connectors are limited to sharing a total of 48A max. (Circuit must support 125% of continuous draw output amperage).


Actually, looking at the manual it seems that I'll either need 100A to a subpanel, or separate 60A branches from the Main for the power sharing. So I guess at this point I'll just go with the junction box / insulated in-line AL/CU splice connectors as Paul suggested above.

power sharing.JPG
 
Actually, looking at the manual it seems that I'll either need 100A to a subpanel, or separate 60A branches from the Main for the power sharing.
No, I think that's just shown as an example. It shouldn't need 100A. The whole point of the circuit sharing is being able to take one line at whatever level it is, and have the sub-units dynamically allocate within that. So you could take one 60A circuit, and put 10 or 15 wall connectors on it, all set as if they were 60A, and they will manage that to stay within the 60A overall limit.

Now all of that is within the caveat that we are talking about a crystal ball into the future because THERE IS NO CIRCUIT SHARING YET. Because Tesla was F'ing stupid in releasing a broken incomplete product in the Gen3 wall connector. They plan to write the code to enable the circuit sharing functionality at some unknown point in the future, but still haven't done it yet, but people are here telling you to use it as if it already exists.
 
Now all of that is within the caveat that we are talking about a crystal ball into the future because THERE IS NO CIRCUIT SHARING YET. Because Tesla was F'ing stupid in releasing a broken incomplete product in the Gen3 wall connector. They plan to write the code to enable the circuit sharing functionality at some unknown point in the future, but still haven't done it yet, but people are here telling you to use it as if it already exists.
Yeah, this is a problem. The alternative is to find the Gen 2 Wall Connectors (you can find them on E-Bay or on the For-Sale Forums here for ~$500 if you look around) and run a twisted pair cable between the two (make sure the cable is rated properly) for power sharing.

Then you can avoid the disconnect switch and just use a Polaris insulated connector at the new work point to join the AL wire to two separate 6 AWG runs to each HPWC.

Power sharing works great, I use it to share a 50A circuit.
 
  • Like
Reactions: Rocky_H
Yeah, this is a problem. The alternative is to find the Gen 2 Wall Connectors (you can find them on E-Bay or on the For-Sale Forums here for ~$500 if you look around) and run a twisted pair cable between the two (make sure the cable is rated properly) for power sharing.

Then you can avoid the disconnect switch and just use a Polaris insulated connector at the new work point to join the AL wire to two separate 6 AWG runs to each HPWC.

Power sharing works great, I use it to share a 50A circuit.
FYI the $500 Gen 2 HPWC is rapidly becoming increasingly rare. In fact, the $600-$700 Gen 2 HPWC is also becoming more rare with the $700+ Gen 2 HPWC quickly becoming the norm as demand slowly surpasses the supply. This has potential to ramp up more quickly so if you need something or think you need it I'd act now.

tldr; The prices on Gen 2 HPWC will never be lower than they are right now.
 
  • Informative
Reactions: Rocky_H
Hi there all and thanks for all the inputs. I've managed to install the system and am expecting town's inspector tomorrow. There were a few little tweaks along the way with the most notable being using this Morris connector that will allow me to add another branch for power sharing in the hypothetical future. It was very straightforward to install. Adding an updated schematic and a couple of photos.

Schematic:
Exhibit 2.JPG

Finished work:
WhatsApp Image 2021-01-23 at 11.34.57 PM.jpeg
WhatsApp Image 2021-01-23 at 11.34.58 PM (1).jpeg
WhatsApp Image 2021-01-23 at 11.34.58 PM.jpeg
WhatsApp Image 2021-01-23 at 11.34.59 PM.jpeg
 
  • Like
Reactions: Dave EV and Rocky_H
Nice! three #4's in a 3/4" = tight :)
I'm thinking you're not reading the different parts of the diagram properly. The three #4 wires are not in a 3/4 inch conduit. That is a XHHW cable, which I think is the buried metallic kind? The 3/4 inch conduit is what was added new, and has the copper wires in it, which are two of #6 and a smaller bare copper ground.
 
  • Like
Reactions: Greyberry