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Dual HPWC Install

Discussion in 'Model S: Battery & Charging' started by wk057, Feb 1, 2015.

  1. wk057

    wk057 Senior Tinkerer

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    So, after some debate over load calculations and a final setup of my new breaker panels I finally have HPWC #2 installed. (Yes, two Model S here.)

    Both units are [email protected] (~20kW). When I installed the first one I had used 1 1/4" EMT from the breaker panel which is sufficient for four conductors of #2 and the #8 ground. This runs to a junction box just behind this wall at the bottom and then splits to 1" EMT to both chargers. (Was originally just one charger with a blank 1" spot left for later.) The bottom ~12" of the wall is actually above the drop ceiling in the finished basement, which made that part easier I suppose.


    dualHPWC.jpg

    (Still have to mount the cable holder for the new one on the left)

    With both running at full power I still only see a 2-3% voltage drop, which confirms that everything is installed well and the transformer feeding my panel can handle the load fine. With these and all other loads I peaked at over 60kW draw so far without issue. I have 400A service here.

    Under normal conditions I don't see both chargers running simultaneously for very long anyway. It's more of a convenience thing for preconditioning and such and not having to switch which car is plugged in beforehand since they have their own chargers. There is a 30A outlet we've been using for the second vehicle's UMC for a while, but this is better.

    For the detail oriented, everyone involved agreed that NEC 625.23's declaration that a portable lockout method for the circuit was insufficient for an HPWC was stupid. All agreed that the 100A breakers and the lock on the breaker panel door were sufficient. The entire panel feeding the HPWCs in my case can be locked out via the adjacent permanently installed transfer switch's off position anyway.
     
  2. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #2 FlasherZ, Feb 1, 2015
    Last edited: Feb 1, 2015
    Looks good. We're about ready to put our second one in for Model X - more on that in a bit...

    A couple of notes for others who see this:

    * First, your choice of 90 degC #2 is required in this case, because when you have more than 3 current carrying conductors in a single raceway, table 310.15(B)(3)(a) requires derating to 80%; 90 degC #2 is rated at 130 amps, which gets derated to 104 amps (just enough to match the 100 amp requirement for 80A continuous loads). It's also a good demonstration of the difference between 90 degC rated conductors and 75 degC rated termination. You're allowed to consider the 90 degC column for conductor derating in a conduit, even though your breakers would consider a maximum of the 75 degC column (since most breakers are rated only to 75 degC). You would not be able to use 4 #3 conductors from the panel because of the derating requirement in a single conduit, and #3 @ 90 degC is 110A, derating would make it good for only 88A - not even good for the 90A rating on the old HPWC's.

    * Second, the junction box must be accessible; it bears repeating because it's not seen in this picture (but I note you talked about it being above a drop ceiling, which is legal as long as it's securely attached to framing members or wall surface above the drop ceiling).

    * Finally, NEC 625's disconnect requirement was primarily designed for commercial EVSE's with OSHA-style tag-out/lock-out requirements. Most inspectors I know agree that it's crazy for home installs where breakers can control it. The AHJ ultimately is the determiner of whether it's reasonable or not. This is why you never hear electricians or "ultimate authorities" on the NEC, because of local amendments and interpretation.

    Now, for my install, I have to do a bit more. I have a considerably longer run and with a second HPWC I'm beginning to bump up against the 200A main's rating on my non-generator panel, as my pool equipment, hot tub, machine shed, and current HPWC (along with some other loads in the home) are all from that panel. So, I plan to do something a bit different. I'll bring in a third service entrance conductor to a 200A main disconnect in the basement (to meet the requirement of all building disconnects being co-located), then place a new 200A panel above my doors in the garage (where my current 125A subpanel is located). From there I'll make the runs down to the HPWC's (and, if I am bored enough, a bell box with a surface-mounted 14-50 outside).
     
  3. wk057

    wk057 Senior Tinkerer

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    Ah yeah, I did forget to mention that I took the derating into account when running the first unit. The wire is #2 90C, of course. The run is ~45 ft total, so, not too bad. There is a ground bus bar in the junction box also.

    The junction box definitely qualifies as readily accessible being in the drop ceiling. It is mounted directly to the wall framing members for the wall behind the first HPWC (right side in this pic).

    As for NEC 625.23, I'm glad most AHJ seem to be reasonable on this with residential installs, including mine.

    My setup is two 200A panels, and the loads were reconfigured during phase 1 of my off-grid solar project so that the two chargers could be put in one panel along with only generic 120V loads of the first floor. The total of loads in the other panel, mostly 240V loads like HVAC and the 2nd floor subpanel for its 120V loads, fit nicely from a load perspective in their own 200A panel.
     
  4. Cottonwood

    Cottonwood Roadster#433, Model S#S37

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    Great comments! Thanks!

    Correct me if I am wrong here, but if you use really good insulation (XHHW-2), this derating is not required. This exception is under the table that you cite.

    Exception: Type XHHW-2 insulated conductors shall not be subject to this ampacity adjustment.

    From looking at Tesla Supercharger plans, they call out XHHW-2 insulation, I believe for this reason.
     
  5. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    That's pretty typical. I'm a bit hamstrung here in that my 2 panels are split based on standby (25 kW genset) vs. grid-only. So by far, the heaviest loads tend to be on the non-generator panel. My meter pan can take up to 5 sets of lugs, though, so I'm good if I need to add more. :) My basement tends to look a bit crazy with all the solar, electrical, and landline equipment:

    20150201_131940.jpg
     
  6. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Is that a DS1 line card chassis on the far left? Our setups are similar, minus the solar. I've got two 200A entrance feeds, one through a transfer switch with a ~20kW genset, so like you I re-wired the panels a few years ago to determine what was on the generator. My current HPWC is going to my grid-only panel. I'm going to need to run a second line from the garage to the basement for the model X.

    I had talked to dominion about a second entrance feed and meter for just the garage and they said no. It's unfortunate, as the transformer is closer to the garage. My service entrance is on the opposite side of the house and I have a finished basement. Running the line for the first HPWC was expensive and required about 15 holes in the ceiling etc.
     
  7. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    You're looking at the text of 310.15(B)(3)(c), not 310.15(B)(3)(a). The text of 310.15(B)(3)(c) refers to raceways subject to sunlight heating on rooftops, which has a new XHHW-2 exception as of NEC 2014. Table 310.15(B)(3)(a) refers to adjustment factors for conductors in a raceway. Page 70-158 is a hellish page in a section that's already difficult to read.

    - - - Updated - - -

    Yes, there's a 25-pair cable coming into the house (demarc up top) and that's an 12-slot box for cards (HDSL2 used here).

    I talked about a second meter and they said I'd be charged for a second service - so I buried my own conduit (at roughly $500/year meter charge, I can bury a lot of conduit, can even pay for the directional boring to make it easy!).

    The mess you see on the bottom of those joists near the panels is the result of moving circuits around to arrange circuits for the genset panels. There are two fairly deep work boxes to move these circuits between panels. If you look closely you can see a few things wrong with the picture, done by the previous owner. One example is the use of schdule 40 PVC water pipe instead of electrical conduit.
     
  8. wk057

    wk057 Senior Tinkerer

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    Nice setup. The 25kW generator panel would certainly force you to shift some things around I would imagine. Fortunately I'm sizing my solar power setup to accommodate both 200A panels under normal loads.

    Not sure if you've seen my other thread here or not: Plan: Off grid solar with a Model S battery pack at the heart

    Here's a few pics from that thread:


    2015-01-14%2001.52.04-1280.jpg

    attachment.php?attachmentid=70761&d=1422592725.jpg

    I'll have 64kW continuous output available (and much higher overload output power), over 3x the inverter output required by NEC 690.10(A) as it requires only enough inverter output to power the largest single load. In this case, a HPWC. Obviously sizing for just that would be silly, though.
     
  9. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    That's a nice setup... and 64 kW is really great. My plant consists of 4 different arrays of panels, total of 18.5 kW. I don't have enough roof space to go above 30 kW. :)

    There's another 9 kW array on the shed roof, not pictured there.
     
  10. anxman

    anxman Member

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    Both of my Teslas have had the dual-onboard charger and I've been debating installing a HPWC at my beach house. Outside of the convenience of the plug, have you found cases where having an 80A charge going (instead of 40A) have been critical?
     
  11. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Originally, I figured there would be - as I go on trips frequently, I find that at least 3-4 times a year, I come back from the airport and we want to leave for my in-laws' (140 miles away) as soon as practical. This was before they installed chargers at the airport, and since then I haven't found a case where it was necessary.

    That said, having a charge cord in the garage that doesn't have to be coiled up and put in the car all the time is the best reason to have something there. I need to have a cord with me for a few places I stay. And with the difference being only $100 between a UMC bundle and a wall connector, I'd opt for the wall connector every time.
     
  12. JST

    JST Active Member

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    I used my UMC as my home charger on a 14-50 for about a year. A few weeks ago, I pulled the trigger on a HPWC (partly because they cut the price, but mostly because my daughter managed to zap herself plugging the UMC into the wall).

    The HPWC is really a much nicer way to charge than the UMC. I agree that it's worth a lot to not have to coil the UMC and put it in the car. Interestingly, I also get a slightly faster charge from the HPWC than I did from the UMC, even with just a single charger. The UMC would show voltage a few ticks below 240, but with the HPWC I am consistently right on 240 (or a bit above).
     
  13. wk057

    wk057 Senior Tinkerer

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    The prongs on a NEMA 14-50 are pretty large. IMO they weren't really designed for often being removed and replaced. Definitely easy to get your fingers in there if you're not careful. I've been hit by 240V a couple of times... definitely not fun.

    You'll see slightly less voltage drop, and hence slightly more wattage at the car, using the HPWC vs the UMC at 40A. The UMC has pretty thin wire inside (#10?) compared to the HPWC (#6). At 40A you should see virtually no drop (~1%) using the HPWC.
     
  14. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I recall that for flexibility purposes, the UMC has 2x 14AWG per leg. A no-no if used for infrastructure, but ok in appliances if it passes the tests.
     
  15. wk057

    wk057 Senior Tinkerer

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    Ah right. Forgot about the parallel conductors in the UMC. The HPWC complies with NEC 625.17 and 400.5(A)(2) if I recall correctly, which gives it a 99A rating using 90C #6 conductors.
     
  16. GreenT

    GreenT Member

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    Am I reading this correctly? Your garage is above a finished basement?

    Isn't that against code everywhere? As the powers that be want to ensure that GASoline (remember that oily sh..) cannot drip down there.
     
  17. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    The HPWC uses a very high-quality cable with conductors that are actually rated for 105 degC operation (at least the first cable I came across). The NEC doesn't recognize anything greater than 90 degC.

    Even then, there will likely be a debate as to whether the NEC can even claim authority over the WC as it is an appliance. The NEC attempts to claim it by saying that the car is the ultimate appliance and the WC is merely an attachment point (e.g., an outlet).

    - - - Updated - - -

    Not necessarily - it's the same in my case... the north wall of my house structure and basement is the south garage wall. The space just above the sill where the joists sit provides room for the conduits to go through the wall.
     
  18. wk057

    wk057 Senior Tinkerer

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    Not directly above, no. It is adjacent to the basement. The garage has a 12' ceiling. A couple of steps in the garage take you up to the first floor. Below the first floor level about 18" and to the garage floor is aligned with the area of the basement level above the drop ceiling. (The garage floor is roughly the height of the drop ceiling.) So, where the bottom of my conduits poke through is actually above the drop ceiling in the basement. Under the garage concrete slab is dirt.

    The 1-1/4" conduit to the right panel in the picture above next to the blue ENT is the one feeding the HPWCs. The blank space above the "Surge Breaker" now has the second 100A breaker.
     
  19. Xenoilphobe

    Xenoilphobe Active Member

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    Great post we are adding a second HPWC as well and this helps understand some options. Right now I have a 14-50 and an a HPWC dropped into a separate Tesla only panel in the garage.
     
  20. wk057

    wk057 Senior Tinkerer

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    It would need to be a 200A panel to run two HPWCs @ 80A. Otherwise you'd have to dial one down a bit.

    Side note, I was running both at 80A today, and the perfectly normal 60Hz hum that comes from my panels and transfer switch under the load freaks out my fiance... lol.
     

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