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Nema 14-50 on 20A Breaker?

Discussion in 'Model 3: Battery & Charging' started by Lewisball, May 9, 2018.

  1. Lewisball

    Lewisball Member

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    Hi guys,

    Need some help. I've gotten two quotes on a NEMA 14-50 install that appear to conflict with each other. One electrician is saying that I can put a 40Amp 14-50 outlet without any upgrades to my panel, the other is saying I can only do 20A with the current load. I have an existing 120V outlet already installed and I don't drive much (~30km a day) but in BC here we can get 75% of the first $750 as a rebate, so I want to take advantage of that. I have two questions 1) Is it advisable to install a NEMA 14-50 on a 20A breaker, are there any downsides aside from slower charging speed? 2) Why is it that one electrician is telling me it won't go over the load? I've pasted the email from the electrician saying I can only go 20A below.

    Trying to make sense of this with very little electrical knowledge. Any advice would be brilliant.

    I did a load calculation and without the EV charger everything is good: 100.42A. Your panel is rated for 125A so there’s lots of capacity there. Adding a charger changes things though, and presents you with some options:
    - If I give you a 240V 20A circuit your total load goes up to 120.42A. This is the max we can get away with. It’s not the greatest charging setup but it’s not bad. Definitely better than a regular outlet that would provide only 15A at 120V. Some information online states it could take 22 hours to get a full charge with a 20A setup (I assume from zero).
    - another option is to install a charge controller that will turn the charging circuit on/off as needed depending on the load of your panel at any given moment. I think I mentioned this when we met, if not I can give you more information. This will give you a 40A circuit but not affect the loading of your panel. This setup is good for about 11 hours charging (again, I assume from zero, both stats came from the same chart). It’s more expensive for sure, the controller itself is about $1200. But it’s the only way we can give you more than a 20A circuit.
     
  2. miimura

    miimura Active Member

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    There are different ways to calculate the allowable load on a panel. If you can get some loads to be considered non-concurrent, then you can add more.

    In any case, if you proceed with the 20A breaker, then you need to use a 20A outlet, which would be a NEMA 6-20. You cannot put a 50 amp outlet on a 20 amp breaker. Tesla sells a NEMA 6-20 adapter for the Gen2 Mobile Connector that is included with the Model 3. That is the lowest friction way to go.

    Model S/X/3 Gen 2 NEMA Adapters

    The table on that page says a Model 3 will charge at 15 miles per hour on a NEMA 6-20. A 120V wall outlet only charges at 3 miles per hour.
     
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  3. Lewisball

    Lewisball Member

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    Very helpful! Thanks.
     
  4. animorph

    animorph Active Member

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    I'd be tempted to go with the electrician that says 40A is OK. Load calcs seem a little fuzzy, and the inspector didn't even check mine anyway. That gets you a valid 14-50 outlet.

    If you are really stuck with the 20A, you might consider a Tesla Wall Connector and wiring for 40A or more. You can set the WC to use the 20A circuit and you are ready if you decide to get a panel upgrade later. No adapters to worry about.
     
  5. bayarea_joe

    bayarea_joe Member

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    You have to know where the 100.42A load is distributed. I would guess 30A dryer, 10A washer, 10A dishwasher, electric or gas range + lights etc. If you are to have all of them turned on, you may not want to exceed 20A as suggested but in reality most people won't have all those turned on while charging (especially midnight)
     
  6. Zippy_EV

    Zippy_EV Member

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    The 14-50 definitely needs a 50A breaker. I personally want enough charger to be able to go from empty to 90 percent overnight. Anything faster is a bonus.

    I installed a Sense home energy monitor a year ago. It is very informative to see the energy a home actually uses over time. (The gadget is not perfect but still neat tech.) I was originally worried that my current 200A service wouldn't allow for Tesla charging at 80A continuous. The electrician said it wasn't a problem for my home's load and he was right. (Happily wall connectors now coordinate so multiple vehicles won't pull more than 80A total. I priced out installing an additional 200A service years ago and am happy to avoid that.)
     
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  7. Graffi

    Graffi Member

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    You need to know what makes up the 100A you are currently using on your panel. It may be that something there is no longer used. Try to get the NEMA 14-50 if at all possible, with the wiring able to handle the load. If they run wiring for only 20A then you will not be able to add more later without changing the wiring to a larger size.

    In my case I have a 200A panel so no problem adding an EVSE 5 years ago. However, we do have a 240v 50A breaker that used to power a Hot Tub that was on the back patio years ago before a re-model replaced it with a patio room. In our case we will re-purpose this circuit for a NEMA 14-50 outlet for the second Tesla. I will run the wiring from garage through Panel back, so only a few feet of wiring. I went ahead and "future-proofed" by getting the size wiring to handle 100A in case we want to install a Tesla HPWC sometime in the future. And to make the installation more versitle, I am installing a 120V 20A outlet piggy-backed off the 14-50 outlet. Of course, it can not be used when the car is charging.
     
  8. Blue in NC

    Blue in NC Member

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    I have a question related to this. I have an electrician coming to install a NEMA 14-50. I will be using the UMC to charge. He has told me he is installing a 40A breaker even though I asked him why it was not 50A. I'm on a 200A panel but it's pretty full. Any insight? Does it matter to me if the breaker is 40 or 50 since I will only be using 32A anyway? Thanks.
     
  9. davewill

    davewill Member

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    You can install on a 40a breaker. The downsides are twofold.

    1. If a visitor wants to plug a 40a EVSE, like the Gen1 UMC, into it, they won't be able to because of the 40a breaker.
    2. If you decided to install a wall connector later, you'd still be limited to 32a charging.

    If 50a is possible with your panel (probably is), I'd go with that, but if it's not, then I'd do the 40a without worry.
     
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  10. Zippy_EV

    Zippy_EV Member

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    #10 Zippy_EV, May 10, 2018
    Last edited: May 10, 2018
    A 50A outlet should not be installed on a 40A breaker. It is a code violation everywhere. You're correct, your vehicle would actually charge just fine as it would be using only 32A but it doesn't make it a good idea. Future someone (say a Tesla buddy with a gen 1 UMC) or someone with an RV would assume that the circuit could support 50A and trip that breaker (or start a fire in the worst case if the breaker doesn't trip and is overdrawing the assumed to be 40A wire.)
    ^^^
    Edit: This was pointed out by Dave to be incorrect. Code has an exception which allows a 50A receptacle on a 40A breaker. I think that's terrible and I'll stand by the rest of the comments. I'd very much recommend installing 50A wire. :)
     
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  11. davewill

    davewill Member

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    You're just simply wrong. I have a 6-50 in my garage on a 40a breaker connected to my 30a EVSE. Installed by the builder of my home. It's a very common install outside of the Tesla community where 30a EVSEs are the norm. It's also very common for things like electric ranges that only need a 40a circuit.
     
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  12. Zippy_EV

    Zippy_EV Member

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    #12 Zippy_EV, May 10, 2018
    Last edited: May 10, 2018
    It's not electrically dangerous to undersize the breaker IF the wire supports the full draw of the outlet (aka 40A breaker, 50A wire, 50A outlet.) But it is a bad idea to install a 40A wire and 40A breaker with a 50A receptacle.
    ^^
    Edit: This 40A/40A/50A receptacle was pointed out to be acceptable according to code. If one goes down this route I'd write on the receptacle to limit to 40A.
     
  13. davewill

    davewill Member

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    #13 davewill, May 10, 2018
    Last edited: May 10, 2018
    Strike two. Sorry to say you're wrong again. The wire size only has to match the breaker.

    Edit: I wish you were right, then I would have the 6 gauge wire I needed to upsize my breaker, and could consider upgrading my EVSE.
     
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  14. Blue in NC

    Blue in NC Member

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    First, thanks to both of you for the quick responses. And just to be clear, the wiring will be 6 gauge so I don't think it am worried about 40A wire but it was the actual breaker that had me confused. The electrician told me that I could always change to a 50A breaker later if I needed it. I guess I just didn't understand, why not do that from the start?
     
  15. davewill

    davewill Member

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    Sounds like a good plan, although I would probably just have him use the 50a breaker. Some people prefer to size the breaker to the appliance, even though there's no requirement to. It has the benefit of (possibly) protecting the EVSE and it's cable from an overload.
     
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  16. Blue in NC

    Blue in NC Member

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    Great, super helpful information. But then I guess if I ever wanted to move to a UMC Gen 1 or the pig-tailed HPWC (and charge at 40A), I would need to change the breaker to 50A, correct?
     
  17. davewill

    davewill Member

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    Yes, exactly. Ask the electrician whether changing the breaker later would require a new permit and inspection, if not you might want to just roll with the 40a. If he knows you plan to upgrade, he might just do the 50a now.
     
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  18. Zippy_EV

    Zippy_EV Member

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    Hmmm. I looked it up and Dave is correct that there is a code exception allowing 50A receptacles on 40A breakers. Yuk.

    I would still use 50A wire. The cost difference would be minimal and it would allow future change to a 50A breaker.
     
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  19. ai4px

    ai4px Wes

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    You can certainly run a 14-50 outlet on a 20amp breaker and corresponding (existing) 12AWG wiring. Remember the breaker protects the WIRE, and 12AWG wire can carry 20 amps (14awg can carry 15amps). So follow me on this... if you already have a wire from your breaker box to your charging location, you can easily re-purpose that wire to do 220 by switching the breaker to a dual breaker and moving the white wire to the 2nd leg of that new breaker. So the answer is *yes* you can convert a 120v feeder to your garage to 220v and put a 20 amp (or 15 amp) 220v breaker on it. Make sure it's the ONLY outlet that reconfigured line feeds. You don't want to accidentally figure out that one of your 110v outlets now has 220 on it. So only do this if you KNOW there's only one outlet on that feeder.

    On to the next aspect... If you re-purpose the wire as I mentioned above, you will not have the "neutral" wire. This means that if you install a 14-50 outlet the neutral will be left unconnected. Some inspectors may not like this. The correct (by the book) feed for the 14-50 requires 4 individual wires. Since your re-purposed wiring will only have 3, the solution is to install a 6-20 or 6-50 outlet instead. You see, the 14-50 is intended to provide 120/240 whereas the 6-50 is intended to supply 220v only. Using the 6-20 or 6-50 plug means that every wire has a place and ever place has a wire. It'll keep the inspectors happy. Many people just install the 14-50 w/o the neutral. I did and I labeled it as 220v only.

    You can then set your EVSE equipment to only permit 16 amps on a 20 amp circuit and you're all set.

    Hope this makes sense and isn't too verbose.
     
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  20. davewill

    davewill Member

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    #20 davewill, May 10, 2018
    Last edited: May 10, 2018
    That you cannot do. There is an exception for running a 40a breaker on a 50a outlet and a 25a breaker on a 30a outlet because outlets don't exist for those amperages. Otherwise the outlet has to match the breaker. However, you can install a 20a outlet, then buy the proper adapter from Tesla.

    I can safely say that ALL inspectors won't like it.
     
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