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Pre-wire for 80 amps?

Discussion in 'North America' started by KP_SB, Sep 20, 2016.

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  1. KP_SB

    KP_SB New Member

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    While I wait for my Model 3 I wanted to get my garage wired up for EV charging. My question is focused on whether or not its worth it to pre-wire for 80 amps? My initial plan is to charge my M3 during the night at 40a via a NEMA 14-50 outlet; however as I learn more about how I use my Telsa and its charging needs I want to be able to upgrade to the HPWC @80a without having to re-run the wires (would only have to upgrade the circuit and install the HPWC). Anyone have thoughts on this? I understand that 2 AWG for 80a is much more expensive than 6 AWG for 40a; but again, is there any negative implications to setting up a 80a charging infrastructure and only actually using 40a?

    Also, I know I need to conduct a proper assessment of my electrical panel and total amp capacity. I'm keeping these considerations separate as I would definitely get that research done pending feedback on the above question. Thanks!
     
  2. KJD

    KJD Member

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    The only downside as you said is the cost. The 2 AWG is also a pain to get bent into place and into the attach points compared to 6 AWG. Good thing you only have to do that once.

    In my garage I put in a sub panel and then NEMA 14-50 outlets in each of the stalls. That way no matter where I park there is an outlet close by. This will also come in handy if I buy a 3 to park next to the S someday.

    Make sure you check out the home charging FAQ. Lots of good information there.
    FAQ: Home Tesla charging infrastructure Q&A
     
  3. TexasEV

    TexasEV Active Member

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    You might want to wait until the Model 3 specs are announced. If you're having work done on your garage now, the electrician can run a conduit from the panel to a junction box in the wall. Then when you order your Model 3 and decide what circuit you need they can come back and install the breaker, run the wire through the conduit, and install either the outlet or a direct connection to the HPWC.
     
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  4. animorph

    animorph Member

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    The HPWC can't charge any faster than the charger in your car will accept. For current Model S and X that's 48A for the standard charger and 72A with the upgraded charger. I haven't seen what rates the Model 3 might be capable of, but it surely won't come with 80A standard. So 80A may be useless to you. Using 80A capable wiring won't hurt anything, and might help if you add a second Model 3 to your garage with a second HPWC. Then both cars could possibly charge at 40A. Supercharging bypasses the onboard charger, so it does not have the same limitation.
     
  5. KP_SB

    KP_SB New Member

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    I forgot about the on-board charger factor but like the fact that pre-wiring for 80a will help with additional future EV purchases. We two cars in a two car garage and we're both adamant about transitioning to EV transportation only so it'll happen overtime. Thanks
     
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  6. Drucifer

    Drucifer Active Member

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    I think 2 40s with NEMA 14-50R outlets is more practical. Then if you have 2 EVs in the future, you are covered.
     
  7. brucet999

    brucet999 Active Member

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    When you say 80A, please be aware that you must wire for 100A circuit in order to get 80, just as you wire for 50A to get 40. For constant loads, the allowed limit is 80% of rated amperage. That's why the car limits amperage to 40 when plugged into a NEMA 14-50 outlet.
     
  8. Saghost

    Saghost Active Member

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    Pretty sure there's no drawback except for the cost of running the heavier wire (and the extra trouble bending it.)

    If you have the panel capacity for it, I'd probably run the heavier wire now (assuming there's a reason you're doing the wiring now in the first place) - it'll probably come in handy later.

    If a second EV comes along, the new HPWCs can be master/slave rigged on the same circuit and share the power dynamically.
     
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  9. adiggs

    adiggs Active Member

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    After 3+ years of driving the Roadster as our primary vehicle, I'm finding that my own thinking about what charging resources I need to have available is going in the other direction. Overnight charging will take me from empty to full in 5-6 hours (8-10 hours for S/X), but even using 1/2 of a charge in a single day is an extraordinary exception.

    And that's on a single vehicle. Our second car is getting ~1k miles per year. My thinking right now is I can charge the second car from a 110 outlet just fine. Anytime the second vehicle is low on battery and I want to be able to use it again soon, it can go into the garage slot with the 14-50 outlet for a faster charge.

    I wouldn't really have thought about it that way 4 years ago before getting the Roadster, but while it'd be nice to have the ability to charge both cars at 40a, I'm no longer willing to pay for panel upgrades if the already wired panel can't handle 2 14-50 circuits.


    Of course, there are very good reasons to have 220 service for every parking spot. Just pointing out another point of view on this. The question I'd be asking myself, is how much use does the second most used car get in the house hold, when one car is effectively always being used. And therefore, how much charging capacity does that second car really need on a routine basis.
     
  10. ApauloThirteen

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    #10 ApauloThirteen, Sep 20, 2016
    Last edited: Sep 20, 2016
    Agree, and even then that might be overkill depending on your daily driving. That's what's missing here - what are your expected daily driving reqs?

    If you assume the Model 3 has 193 or so miles of range (Say max of 215, and you charge 90%), how often would you drive that much and come home and need to turn around the car that fast? You will likely have the supercharger options driving far from home. And every morning with home charging, you're back to full/90% again.

    Our household will likely have 2 fully electric cars with 200+ miles of range soon. I think we still only need one charger and only need to charge one car (swapping every other night) per night. Doesn't matter if the charge takes 2, 4, 6 or 8 hrs at that point, the car would still be ready to go by 6-7 am.
     
  11. Drucifer

    Drucifer Active Member

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    Very good point. Last summer I had a single 220/16 amp EVSE (3.3 kW) on a 20 amp circuit Even with that, I charged my Model S on Sunday, Tuesday and Thursday nights, and my wife charged the Chevy Volt on Monday, Wednesday nights and during the day on Friday and Saturday (she works from home on Fridays) and we never got even close to having a problem.

    That said, if you have TOU billing or just want it to be convenient, it is nice to have 2 EVSEs....but even though I have dual chargers (80 amp capability) in my Model S, I have had occasion to use it exactly one time in the last two years. It really isn't necessary unless you drive 200 miles a day, 2 days in a row or more on a regular basis, and even then, it might be overkill.
     
  12. hcsharp

    hcsharp Active Member

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    I think you should pre-wire for 80A. Sure #2 or 3 wire is a little more expensive but the biggest cost is the labor. If you're paying for the labor anyway you might as well put in larger wire to give you a cheap option in the future.

    The argument that two smaller outlets (such as two 14-50s) is more practical makes no sense. Just because you put in the larger wire doesn't mean you can't install an additional 14-50 outlet or HPWC. If your panel doesn't have the capacity for both, then you can easily set your HPWC up for load sharing. If you don't like that idea, change the max current for your HPWC by giving it a smaller breaker and re-setting the dial or dip switches inside. Then you will always have the option to increase it some day.

    Depending on where you live and other circumstances, a 72 or 80A charger is also more practical for visitors. Suppose your adult children [substitute other friends or relatives] want to come visit you for dinner but it's a long trip. 72A will be a big help so they don't have to stay half a day or overnight. Not your situation now? You have to think of the future when virtually everybody will be driving EVs.

    I live approximately half-way between Montreal and Boston. It used to be common for me to get people stopping here for 70 or 80A on the way. I rarely need 80A myself, but I'm happy to have enabled a lot of other travelers. It's not a bad idea to think about more than just your own needs. And the few times I did need it myself, I was glad I had it.
     

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