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Duel HPWC 80amp wire size to sub panel?

Discussion in 'North America' started by DocJR, Jun 27, 2018.

  1. DocJR

    DocJR Member

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    Im set for delivery on a MS85 (duel chargers)in a few weeks. My wife has MS100D. Im thinking about duel HPWC in our finished garage. The panel is ~50-75 feet worth of wire run through the garage attic to location. Im thinking sub panel, then split with conduit to each HPWC. Any thoughts on wich AWG to go to sub panel? I was thinking 2awg copper to panel, 3awg to each unit.
    Im new here, thanks for help!
     
  2. SSedan

    SSedan Member

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    Seems like a solid plan.
    You are planning on having the HCWC on one circuit and communicating right? In which case the sub panel serves as a disconnect.
     
  3. 365gtb4

    365gtb4 Member

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    2 gauge should handle 80 amp continuous load to sub panel. 3 gauge to each HPWC will work if they are close to the panel.
     
  4. DocJR

    DocJR Member

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    Communicating, exactly. Would I put a disconnect switch at the sub or another 100amp breaker there? Both? I want the potential for either the master or slave to ramp up to 80 amp when possible. My wife mainly uses the local Supercharger so she may not even plug in at home much.
     
  5. DocJR

    DocJR Member

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    Great! Yes, the 3 Gague would be less than four feet for each charger, at least ideally.
    Thanks!
     
  6. bigdaddie

    bigdaddie Member

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    I used 3 gauge on mine and it BARELY fits in the HPWC connectors. I had to run through a couple of 90 degree bends and that stuff is tough to work with. It is also very difficult to maneuver within the HPWC housing. Good luck, have fun!

    BD
     
  7. DocJR

    DocJR Member

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    Thanks BD! How big is your circuit breaker? And how many amps are you getting?

    I chatted with an electrician, he mentioned that new code allows some 4 gague copper wire to run 100 amp. I wonder, if it’s true, it would be thinner for the conduit run and housing. Anyone know about this?
    Thanks
     
  8. eprosenx

    eprosenx Member

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    Lots of comments here:

    Would this run through the attic be in conduit? That makes a huge difference. If it is just NM (Romex) or SE type cable it must be limited to the 60c insulation rating limits and so that makes the sizing requirements much larger.

    For 60c limits you would need 1 AWG copper to get 100 amps (it is actually rated for 110). 2 AWG is only good for 95 amps so it is not acceptable for a HPWC at 80 amps since that 80 amps is continuous which means you need 25% more ampacity. You could also do it with 1/0 aluminum which is rated to exactly 100a at 60c. You can't run aluminum direct into a HPWC, but you could take it to a subpanel or I think you can also just pigtail splice it to copper to get the last distance to the HPWC. You need 3 awg copper in conduit to feed the HPWC at the full 100a. I don't think it will accept any wire larger than 3awg.

    So for your run to the garage from the main panel, if all in conduit you could do 3awg copper or 1awg aluminum. If NM or SE cable you would need 1 AWG copper or 1/0 aluminum.

    http://www.barr-thorp.com/wp-content/uploads/2011/04/digest-176-nec-tables.pdf

    Assuming you have enough available capacity to your house in general (you need to run load calculations) then a really good solution might be to run an aluminum feeder from the main panel to a sub panel (or even just a splice point / split point) in the garage, and then to run 3 awg copper in conduit to both HPWC's and have them linked by RS-485 to share capacity.

    One benefit of having a panel in the garage is that it could count as the disconnect. For breakers feeding a HPWC at *over* 60a you have to have a disconnect readily accessible that can be locked in the off position. I interpret this as a "lock off" device in the main breaker panel is sufficient, however, some AHJ's (authorities having jurisdiction) want the disconnect close and within visible range, etc... You could also reconfigure later if you get a different vehicle charger that did not speak the HPWC coordination protocol. You could downgrade the remaining HPWC to a lower amperage (through settings) and have a second breaker in the panel for some other kind of charger or plug.

    P.S. You also might need to do the calcs on correction factors for the cable running through the attic since it may get hot. Though typically NM and SE cable is actually thermally rated to a higher temp even though code says you can only use it at the 60c rating. The higher rating still applies for doing the temperature correction factors.
     
    • Informative x 2
  9. DocJR

    DocJR Member

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    Thanks for the info. Decisions decisions (im already planning on bringing in an electrician)
    I’d prefer to have less conduit showing in the garage, so I could do conduit in the attic. If so, 3 awg homerun in conduit to to sub to run 2 HPWC’s is ok?
    If not I could do the non conduit aluminum 1/0 NM run, but anyone know if there are problems switching over to copper at the sub (I think most main panels are aluminum to copper anyway)?
    I appreciate the wealth of knowledge here!
    Thanks
     
    • Like x 1
  10. eprosenx

    eprosenx Member

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    Copper is crazy expensive (especially now) so a lot of these larger feeders are done with aluminum (so say aluminum from your main electrical panel to the sub panel - but really either works and copper is superior in most respects). You also have to figure out how to get the big feeder wires into your main panel. If you use aluminum conductors which are LARGE you need to be able to route them in your panel.

    Note that if you use NM or SE cable you can't run it exposed anywhere, so it has to be in wall.

    If you do aluminum from the main panel to the sub and then copper from the sub to the HPWC's that would be fine. That is likely how all the circuits in your main panel work today (though some of the higher amperage stuff like ovens and AC might be aluminum branch circuits like in my house).

    I think it is fine to feed the sub with a 100a breaker and have a single 100a breaker out of it going to both HPWC's or actually, I might just do two output 100a breakers, one to each HPWC so I did not have to use split bolts to junction the two sets of wires together. You would still link both HPWC's so they shared usage information such that in total they never drew more than 100a. This would just be a nice clean install.

    I think you are going to end up with exposed conduit in the garage since you have to use 3 AWG copper wire to do 100a to the HPWC units which then has to be in conduit to support 100a on 3 AWG. You could always do smaller wire and set the HPWC's to a lower setting (and would let you use NM cable in wall if you wanted), but it is all a matter of what you want to spend and how you want to future proof. I personally think surface mount EMT conduit does not look bad.

    Also, depending on wire gauge you end up using for the feeder and the amount of available capacity in your main panel, you might do like a 1/0 copper feeder to the sub panel on a 125a breaker in the main panel. That would give you a little extra capacity in case you ever wanted to put two chargers on 60a circuits, etc... (again, it all depends on your total available capacity in your main panel - but there is nothing wrong with overbuilding the feeder to the garage if you think later you might upgrade your main electrical panel service, etc..)
     
  11. DocJR

    DocJR Member

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    Thanks for the wealth of knowledge. Yes, I believe there will be a growing need for this panel in the future, so I’d rather do it right the first time. The only thing holding me back now would be project budget.
     

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