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Future proof wiring

Discussion in 'Model 3: Battery & Charging' started by sailr, Jun 10, 2018.

  1. sailr

    sailr Member

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    I have a 200 amp panel in my basement. I am planning to get a 50 amp breaker added to the panel with one 14-50 outlet in my garage for now. I think it should be about 20-25 feet from the panel to the planned outlet location. I plan to have only one Tesla(Model 3) for the time being.

    My question to the forum members is, whether can I future proof the wiring now? What size wiring should I use? The plan is to replace the 50 amp breaker with a 100 amp breaker and also add a sub panel in the garage at a later date if I have more than one EV.

    Also, with the 50 amp breaker, can I have two 14-50 outlet installed(daisy-chained), with the intention of using only one at a time? Will this be according the the code?
     
  2. electracity

    electracity Active Member

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    Tesla wall connector are designed for power sharing between multiple cars. You can read the manual online. One option is to put in a simple 14-50 today but have the electrician use a wire gauge appropriate for a 70 or 80 amp circuit in the future. Although most people with two cars would do fine sharing a single 50 amp circuit.

    From appendix B:

    The Wall Connector includes a feature
    whereby Wall Connector to Wall Connector
    communication allows you to split the
    maximum available load over a maximum of 4
    Wall Connectors. The wire used for this local
    network must share the main power cable
    conduit or be housed in a separate conduit. In
    other words, the high voltage wires must be
    branched to a junction box from each
    individual unit.
     
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  3. eprosenx

    eprosenx Active Member

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    Great question! I have been thinking about this A LOT in the context of preparing to build my own new home. Optimally, I would run a 100a capable set of wire to each vehicle parking spot, but this comes with caveats.

    Copper wire is *stupid* expensive right now. So for these high draw circuits it is tempting to think about aluminum. One of the issues with aluminum though is that you need significantly larger cable for the same ampacity and so you need more working space to deal with the wire and you need to have breakers and devices on the end with large enough terminal lugs to accept the large cable. So I don't think a AWG 1 or a 1/0 "one aught" aluminum wire is going to fit under NEMA 14-50 terminals (which size you need would be based on whether you can use the 60c or 75c rating). You could potentially splice it to some smaller gauge aluminum or copper right at the end, but that would require a decent size junction box.

    I can't find specs on the Wall Connector for what the max gauge wire it accepts is, but I think it is 3 AWG since it says to use 3 AWG copper if you are going to do a 100a circuit to it (it can accept basically any smaller size circuit as well - it is configurable). I should also call out that 3 AWG copper is only good for 100a at the 75c insulation rating, so that means you can't run ROMEX (NM style cable) since it is only allowed to be used at the 60c rating.

    So the options I see are: 3 AWG copper in conduit so you can use the 75c rating (I think MC counts), or aluminum (I think the same rule applies so you would need 1 aught if not in conduit (i.e. like in romex type wire) or 1 awg (which is one size down) if in conduit. Then you would have to adapt that to smaller wire on one or both ends to actually make use of it.

    The questions are severalfold: How hard is it to run stuff from your main panel to the garage? With an uncertain future, perhaps you should just do the simple solution today and add more later if needed. I would also call out that I like keeping a UMC in the car with me at all times and you don't want to be disconnecting it every day, so that would encourage the purchase of a second one. I might suggest buying a wall connector rather than a UMC then which would allow you do charge faster anyway... This is what I did, and I did a 60a circuit so I could max the charge rate of my M3.

    Depending on what other car you get in the future (Tesla or not) your charging design could be vastly different. Maybe you need a J1772 charger for the other car and it can't communicate with the Tesla charger. So two Tesla Wall Connectors can share a single circuit since they can talk to each other, but other products could not.

    It also depends on the total calculated load for your house and how much remaining capacity you have available. In an optimal world, each EV would be on its own circuit and have sufficient capacity to charge at the max rate of the vehicle. You only want to link chargers if you don't have enough branch circuit or overall feeder capacity and so you want to load share to reduce total load.

    ... yeah, so it is complicated ... I installed a Wall Connector outside on a 60a breaker with conduit and 6 gauge copper wire, but then just for funsies installed a NEMA 14-50 on a 50a circuit inside of my garage just in case I park the car inside or I want to test the UMC or have a friend over that wants to charge... I frankly did not run the full load calcs for this, but my logic is that it would fall under the non-coincident loads exception where if two things will never run at the same time you only have to calculate for the higher draw load (like heating and air conditioning).

    I also used 6 gauge copper wire on the 50a NEMA plug since the plug I used turned out to be kind of crummy and only had 60c rated terminals. Since I ran it in conduit, if the terminals on the plug had been rated at 75c I could have gotten away with #8 gauge (the breaker is rated for 75c anyway). Though I likely would have done 6awg anyway for such a short run...

    No. This is explicitly not allowed in the 2017 National Electrical Code.

    625.40 Electric Vehicle Branch Circuit - Each outlet installed for the purpose of charging electric vehicles shall be supplied by an individual branch circuit. Each circuit shall have no other outlets.
     
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  4. davewill

    davewill Member

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    If you want to do this, is go ahead and do the subpanel now. That gives you a place to terminate the bigger wires, then you can run the smaller wire a short distance to the 14-50. When it's time to upsize, just rerun the short distance.
     
  5. electracity

    electracity Active Member

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    I feel that 100 amp total in a two or three car garage will easily cover the charging needs of 99.9% of households. 200 amp plus in the garage is going to require a main service upgrade for almost everyone. Power management is increasingly sophisticated and two or three EVs sharing 80A of power should not inconvenience anyone.
     
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  6. eprosenx

    eprosenx Active Member

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    This is actually a really good idea if you want to spend the money up front to future-proof and your panel is not already in the garage. You could run aluminum conductor from your main panel to the subpanel and do like a 100a breaker (even up to 125 amp perhaps - that is often the max size branch breaker you can install - though you would need somewhere to land the neutral wire on a big enough lug). Looks like the 100a or 125a Eaton breakers at least can handle up to 2 aught wire (not sure what kind of breaker you have).

    This is a good point. Depending on the load calcs for your house you might not have much "capacity" left as it is for EV's (you need to do the math or have someone do it for you).

    One of the (many) options would be to run 1 aught aluminum wire which if you are limited to 60c insulation gives you 100 amps. Put that into a sub-panel and then run a 50amp breaker off of that to a NEMA 14-50 (perhaps using copper wire the short run). Then later you could add a second 14-50 very easily on its own 50amp breaker. If you do consider the Wall Connector you could do a 60a breaker instead which would let you charge at the FULL 48 amp potential of the model 3. This would be 50% faster than with the 32 amp UMC on a 50amp 14-50 plug. If later you needed a full 50amp plug for a different EV, you could just adjust the HPWC down one notch to only draw 40 amps but leave it on the 60 amp breaker (load calcs are on nameplate values, not on breaker size - and I think setting the HPWC down would count as modifying the nameplate value). That would give you a full 40 amps to use for a second EV charger.

    I will say though, if you are planning on two Tesla vehicles and are going to install two HPWC's then you could skip the subpanel and just do a junction box to put both Tesla units on the same breaker out of your main panel. The Tesla units can just talk to each other and coordinate their draw to ensure it is less than the breaker rating.

    No shortage of options!
     
  7. sailr

    sailr Member

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    I am assuming I have to hard wire the wall connectors to a junction box and cannot use 14-50 with multiple wall connectors. Am I right?


    There goes my plan to to keep the initial install simple and also future proof the wiring part of it! Thanks eprosenx. I really appreciate you taking time to explain the fallacy of my plan and providing additional insight.

    Yes, I am leaning towards this now.

    Dave: One of the reasons I wanted to keep the initial install simple is to keep the upfront costs low. Approx. how much does a subpanel add to the cost?
     
  8. electracity

    electracity Active Member

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    The manual shows how multiple wall connectors need to be wired. You could wire two NEMA 14-50 and later convert to two wall connectors. I can't explain the wiring scheme any better than the manual.

    I did one NEMA 14-50 but with heavy wire so that I can later convert to a higher amp setting using the wall connector.
     
  9. eprosenx

    eprosenx Active Member

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    Wall connectors are intended to be hard wired in. Some folks have put them on pigtails, but I don't think this meets code (according to my reading of the 2017 NEC). I definitely would not do them on pigtails plugged into NEMA 14-50 receptacles the receptacles were sharing a circuit. That is extremely clearly not allowed by 2017 NEC.

    FWIW, I went and looked it up. Here is a very popular 14-50 receptacle. It is rated for copper or aluminum wire, but is only good up to a #4 AWG wire.

    https://www.homedepot.com/p/Leviton-50-Amp-Flush-Mount-Shallow-Single-Outlet-Black-R10-00279-S00/300324414
     
  10. electracity

    electracity Active Member

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    Tesla recommends a higher grade 14-50 plug due to potential daily torque on the plug when the mobile connector is connected and disconnected from the car. This inexpensive leviton plug is more appropriate for plugging in a fixed machine.

    The Leviton plug is probably fine, but not ideal.
     
  11. Moderatefan

    Moderatefan Member

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    #11 Moderatefan, Jun 12, 2018
    Last edited: Jun 12, 2018
    While subpanel itself may be only $100, the standard going rate for electricians to put it in is $1,200 :(
    Some may be willing to put it in cheaper, but in my area apparently all electricians have more work than they can handle, so it's hard to get them to come out or give an estimate...the only ones that come are those who charge triple rates.
     
  12. Marsnaut

    Marsnaut Member

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    I purchased one of these: Leviton 50 Amp Single Surface Mounted Single Outlet, Black-R60-55050-000 - The Home Depot. I'll likely leave it plugged in 99% of the time so I went with the utilitarian approach.
     
  13. davewill

    davewill Member

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    Hard to say what an electrician will try to charge you. The parts are cheap and the labor shouldn't be a big deal. The real cost is in the bigger wire and running it. My comment was in response to you doing the bigger wire, something I wouldn't do unless the cost difference was pretty minimal. I'm generally skeptical of plans to "future proof". It's hard to even be sure you'll still be living there when you add a second EV. Is it really cost effective to spend extra money ($1K, $2K??) now, for something that may happen years from now?

    Of course if you know this is the permanent family home and plan to add the second EV in the next year, then that changes things.
     
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  14. electracity

    electracity Active Member

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    I agree. The sometimes exception is conduit placed in locations that will later be hard to access. (Although conduit underground is usually not usable after a few years).
     
  15. nwdiver

    nwdiver Active Member

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    I helped a friend install a HPWC + 14-50 in his driveway. Since ~90% of the labour was trenching and running cable ~200' to the driveway I convinced him to run 2/0 AL triplex rated to 225A. This allowed him to terminate directly to his main bus using the 200A main breaker as over-current protection for the line we ran. To provide over-current protection to the HPWC the 2/0 is landed on a 100A 'sub-main' breaker in an RV Box that includes a 14-50 outlet. The HPWC is landed directly on the bus of the RV Box.

    IMG_5764.jpeg IMG_5766.jpeg
     
  16. davewill

    davewill Member

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    Interesting. It passed inspection like that I assume? (I have no reason to doubt it, I've just never seen this before) What is the rationale for using such an oversized cable? Thoughts of a second 100a charging circuit, or maybe building a garage there?
     
  17. nwdiver

    nwdiver Active Member

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    No breaker required at the panel since the line has the same rating as the bus, lower line losses and providing the ability to charge multiple cars in the future.
     
  18. eprosenx

    eprosenx Active Member

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    Many questions here:

    Is that neutral conductor larger than the hot conductors? Or is that some weird fisheye camera distortion? Normally I would see it the other way around (neutral allowed to be undersized).

    I am confused on multiple levels though. That looks to me like copper wire? You said it was Aluminum though?

    Also, where are you getting the 225a rating from? That is not matching what I am looking at in the 2017 NEC tables. Typically I see 4/0 for aluminum 200a feeders and 2/0 for copper 200a feeders. Though I think both of those are allowed under an exception that allows the main service to be rated at 83% of what it would otherwise be rated at as long as the entire load of the house is fed from that single feeder.

    2014 National Electrical Code Updates – Wire and Cable | IAEI Magazine
     
  19. nwdiver

    nwdiver Active Member

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    We pigtailed from 2/0 AL to 2/0 CU for the final run because copper is easier to bend. The neutral is the same size... I wasn't there for the final wiring so the pigtail might be a bit larger if that's what was lying around but 2/0 AL triplex was used which is 2/0-2/0-2/0

    The wire rating changes depending on where it's used. This is how utilities can run #4 wire overhead to a 200A service drop...

    Screen Shot 2018-06-12 at 1.00.58 PM.png
     
  20. davewill

    davewill Member

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    It took me a while to grok it. The incoming feed are the two wires terminated on the 100a breaker (hots), the big black wire at the top (neutral), and the stranded bare copper wire (ground) at the bottom. The two black wires that are smaller than the neutral coming from the bus bars at the top (hots) are going to the Wall Connector as is the solid bare copper ground wire at the bottom.
     
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