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

Discussion in 'Supercharging & Charging Infrastructure' started by Greyberry, Jan 12, 2021.

  1. Greyberry

    Greyberry Member

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    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?
     
  2. paulk

    paulk Member

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    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.
     
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  3. paulk

    paulk Member

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    If for some reason you decide to run new wire, upgrade it to support 100amp service and use a subpanel for future expansion. As for now, there’s no point in replacing wiring without an upgrade.
     
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  4. Greyberry

    Greyberry Member

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

    (Point taken re 100 amps)
     
  5. john pane

    john pane Member

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    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.
     
  6. Greyberry

    Greyberry Member

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    Taking it back, Morris connector is not what I need.
     
  7. Greyberry

    Greyberry Member

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    Sorry, can't find a way to edit the post. This might do the trick. It will be fairly easy to add a switch in case of an upgrade. In any case I intend to submit this to the town and obtain their buy-in.
     
  8. john pane

    john pane Member

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    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.
     
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  9. Greyberry

    Greyberry Member

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    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?
     
  10. john pane

    john pane Member

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    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).
     
  11. Greyberry

    Greyberry Member

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    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
     
  12. Rocky_H

    Rocky_H Well-Known Member

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    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.
     
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  13. Greyberry

    Greyberry Member

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    Thanks everyone for very good feedback! Dropped the proposed plan with some schematics at the town's building department. Will see what inspector thinks - will make sure to report back here.
     
  14. Dave EV

    Dave EV Active Member

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    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.
     
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  15. Ostrichsak

    Ostrichsak Active Member

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    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 x 1

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