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Conduit question

Discussion in 'Model 3: Battery & Charging' started by jeanvaljean, Aug 31, 2018.

  1. jeanvaljean

    jeanvaljean Member

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    Hi everyone,

    Getting my charging situation set up, Model 3 hopefully coming in a few months. I want to install a NEMA 14-50 in my garage interior wall. The four electricians I've talked to all suggest using Romex 6/3.

    I have a 200amp panel in the basement, about 80 feet from the garage, with an open slot. The work, as far as I can, is to put in a 50 amp breaker, run Romex 6/3 from the panel, through an unfinished part of the basement, penetrate the garage wall, run it to the spot where the outlet will be, and put the outlet there.

    I've gotten several wildly different quotes from electricians, anywhere from $1600 to $750, including the cost of the Romex.

    I'm obviously going to ask the electrician this, but thought I'd ask you guys these 2 questions:
    1) From the basement panel to the garage, I assume the Romex doesn't need to be inside any type of conduit, right? Googling the NEC (Understand the Code Requirements for Wiring in Exposed Locations) says that in unexposed areas, it's ok to use it unprotected.
    2) Once the wire hits the inside of my garage, it seems "exposed" to me - at this point, should it be in a conduit? I see a lot of stuff online about how Romex shouldn't be in a conduit due to heat build-up - but also about how it should be properly protected in exposed locations. Which is it? I have two young kids and I don't want them being able to touch the wire.

    thanks!
     
  2. sootless

    sootless Member

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    Interesting question. From the link you sent I read it as anything that isn't in the walls or ceiling joists should be in conduit. I never knew. Why not just run conduit? It might even be cheaper as the THHN wire is less than romex.

    Have you considered running 3/3? It may seem like over kill but will have a few advantages. Less heat loss, cheaper to run and the potential to increase the amps later if you decide to go with a larger charger or multiple cars. The price difference isn't all that much.
     
  3. eprosenx

    eprosenx Active Member

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    NM cable (romex) is allowed in conduit. This is a common misconception.

    It just does not make sense for long runs. If you are all in conduit, then THHN is the way to go. But for this use case of mostly romex but then a short exposed section, it makes sense. (I would prefer not having a junction splice to THHN)

    I would have to go read the NEC article on NM cable in detail, but yeah, I think in basements with exposed joists it is often ok to run romex exposed (there are rules around size too - small cables they may make run through the rafters, but large cables can just run below them).

    The most bulletproof way to do this would be to run this in 3/4in EMT conduit with say 6awg (actually would allow a wall connector up to 60/48 amps setting) but that may be overkill and a waste of money.

    I would not worry about romex in conduit heat wise since romex is rated to 90c on the insulation, but code only allows it to be calculated as if it were 60c rated so it is already massively derated due to its ability to be installed in thermal insulation (which does not sound like it applies to your situation).
     
  4. jdcollins5

    jdcollins5 Member

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    NM cable is considered to be its own raceway and does not need to be in conduit. It is fine to run NM cable in exposed basement and garage areas in most states.

    If you feel the need for conduit then use THHN wire.
     
  5. voidptr

    voidptr Member

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    What's the finish in your garage?

    If you're running the romex inside an un-drywalled stud-bay, it's considered protected in most jurisdictions, although some towns only allow that for vertical runs; if it's running between multiple studs, the wall should be finished to enclose it, or the horizontal run should be 7 feet or more (can vary by jurisdiction) above the floor. Reason is to avoid owners using the wires as hanging rods, putting rakes behind them, etc.

    If you're running it on top of drywall, I'd reconsider and fish it inside the wall, run it through a conduit for a few feet, or put a junction box on the wall where the run enters the garage and switch to THHN inside conduit at that point.
     
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  6. jeanvaljean

    jeanvaljean Member

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    Thanks everyone, really useful insight.

    My garage is finished drywall, and I was planning on having the wire run on top of the drywall. I think I'll ask the electrician to run it through conduit once the wire gets to the garage.

    Now only if the damn car would come ...
     
  7. bkmartin

    bkmartin Member

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    I’m not sure why you wouldn’t just fish the romex through the drywall. This is going to look the best and is not that difficult.
     
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  8. Toadmanor

    Toadmanor Member

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    How do you fish romex through the drywall?

    I am also getting into a garage with finished walls and I was just going to put the 14-50 where I come in from the basement. But, if one can easily fish through drywall I would rather put it in another location.
     
  9. bkmartin

    bkmartin Member

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    To fish through drywall, it depends on if you have access to the top or the bottom of the wall. In my case, I had access underneath in my crawl space. You cut a small hole at the bottom of the drywall (adjacent to a stud), drill through the bottom plate of the wall and into your crawl space. Cut another hole where you want the outlet (adjacent to a stud). Push wire from the crawl space to the first hole, attach fish tape/rod to the wire using electrical tape and pull wire up to the outlet hole. Check YouTube for examples.
     

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  10. Toadmanor

    Toadmanor Member

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    Yes, I got that but I was hoping to fish it horizontally across several studs.
     
  11. Randy Spencer

    Randy Spencer Active Member

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    I just got 50 feet of 6/2 for $100 and a 60 amp breaker for another $60, normally $20, but I have an antique box. I fished the wire thru the bit of conduit down the side of the house. Hung the rest of the wire from plastic zip ties and right down the stud into the Tesla HPWC in the garage under the house. Plus tax, still less than $200. 6/2 is great for the HPWC, you want 6/3 if you are energizing a NEMA 14-50, as you may plug your RV in one day and your 110v outlets won't work without the neutral wire. Of course, it's another $50 for that one extra wire.

    -Randy
     
  12. eprosenx

    eprosenx Active Member

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    6 gauge romex is limited to 55a of capacity (44a continuous). Normally you would install a 50a breaker and do 40a of charging if you were limited to 6awg romex with a hpwc.
     
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  13. SSedan

    SSedan Member

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    Home charging setup, challenging conventional wisdom.
    This is a thread I started a week or so ago.
    Short version I would build in some extra capacity when running the wire, maybe you get a free HCWC later or just decide you want one and if you run wire capable of handling 60amps today which should be a small cost up-charge now, later it is just a breaker swap and mounting the HCWC and get 50% faster charging(48amps from a 60amp circuit).

    Yes 32amps is enough for pretty much everyone's daily drive, planning for just today is short sighted though.
     
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  14. mongo

    mongo Well-Known Member

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    With the right (long, flexible, with a pull eye) drill bit, the electrician can run it in the wall with access holes every other stud bay. Or, one can cut a horizontal slice out of the drywall, drill the studs, run the NM-B, then put the drywall back and mud the seams.
     
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  15. eprosenx

    eprosenx Active Member

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    I am assuming though this is even more of a royal pain if there is insulation in the walls though.

    This is why in garages I generally just do EMT exposed.
     
  16. mongo

    mongo Well-Known Member

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    Yeah, drilling with insulation can be a mess. Blind drilling runs the risk of 'finding' other circuits too...
     
  17. voidptr

    voidptr Member

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    Personal opinion, but drywall repair isn't that hard; it takes a couple days just because you need to let the joint compound set overnight a couple times.. Cut a 1 foot horizontal strip out of the drywall with a drywall saw or utility knife, drill and run your wire, screw the strip you cut out back up, tape and joint it.
     
  18. sootless

    sootless Member

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    I do think 3/3 romex is worth the extra cost for the following reasons.

    1. Future expansion. 3 gauge will handle 100 amps allowing you to do 2 cars if required.
    2. Safer. You are well below the wire capacity at 48 Amps. The wire will run cooler.
    3. Cheaper to run. The voltage drop/power loss is about 1% less. About 1 cent on every dollar will be saved. Over 5 or 10 years the wire should more than pay for itself.
     
  19. Sophias_dad

    Sophias_dad Member

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    If you use setting-type joint compound, you can be done in an evening, although you should probably wait overnight before painting.

    I agree that opening and reclosing a wall is not that hard. If you are careful, you can begin/end your strip at the midpoint of joists and then you only need a piece or two of strapping to span the joists.
     
  20. eprosenx

    eprosenx Active Member

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    3 gauge romex (NM cable) is *not* rated to 100 amps. It is only rated to 85 amps at the 60c insulation rating (which you are required to use the 60c column for romex). 3 gauge in conduit can use the 75c column which *is* rated to 100a.

    The NEC is already very conservative. I have no issues worrying about the safety of an install if done strictly to NEC requirements. I use 6 AWG in EMT conduit and I have never felt the conduit being warm.

    I am very hesitant to make the argument about loss being lower to the point where it pays for larger gauge wire. It depends on a LOT of factors. If you spend $800 a year on power AND you can make the argument that you get 1% *less* loss with larger wire (which I question for most installs if that is feasible) then that is only $8 a year. If you spend $100 more in wire, that is a pretty long payback (not even factoring in time value of money).

    Now with that being said, I often am a fan of increasing wire sizes for future proofing and for the other reasons listed above, but I don't think it is necessary for safety and I am not sure about the ROI on the wire upsizing just for that reason.
     
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