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Repurposing an electric oven 40A circuit for charging

Discussion in 'Model S: Battery & Charging' started by Discoducky, Oct 30, 2012.

  1. Discoducky

    Discoducky Active Member

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    #1 Discoducky, Oct 30, 2012
    Last edited: Oct 30, 2012
    What is the biggest amp outlet i could use? 125A sub-panel is full otherwise, but outlet would be only a few feet away and charge cable wouldn't need to be longer than 10 feet.
     
  2. strider

    strider Active Member

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    So the breakers are 40A? I would suggest installing a 10-30 or 14-30 so you'd be charging at 24A.
     
  3. earthling

    earthling Iam Notdesi

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    Great question. That makes me wonder about my unused electric dryer outlet too. Although I think dryers use less juice than ovens. How about it, anybody in the know?
     
  4. Lloyd

    Lloyd Active Member

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    #4 Lloyd, Oct 30, 2012
    Last edited: Oct 30, 2012
    Get some 1/2 width breakers to make room for your outlet. Unless your panel is already full of 1/2 width, the you should be able to make room. You can't use the oven and plug on the same circuit!
     
  5. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #5 FlasherZ, Oct 30, 2012
    Last edited: Oct 30, 2012
    You cannot install a new NEMA 10-30R receptacle; you may only replace one that was installed/added prior to NEC 1996. Adding a new permanent NEMA 10 series receptacle (30A or 50A) will fail inspection. Furthermore, with only one exception -- 15A receptacles on 20A 120V circuits -- the overcurrent protection (breaker size) must be equal to or less than the receptacle's rating. You are not permitted to install a NEMA 14-30R on a branch circuit with a 40A circuit breaker, it will fail inspection.

    - - - Updated - - -

    The NEC is fairly specific about certain appliance outlets. As Lloyd said, you may not share certain appliance circuits for another purpose like car charging. You may repurpose the breaker, and wiring accordingly to move the circuit if you need to. For general purpose use, you may wire multiple receptacles on a single branch circuit (for example, you are permitted to have 2 NEMA 14-50R's installed on a single branch circuit - but that breaker MUST be 50A and you couldn't draw more than that across both outlets). I would have to look deep in my NEC book about the dryer outlet, but I do know that a residential installed range/oven is not permitted to be shared with a second receptacle.

    Your best bet -- if you don't use the electric dryer outlet -- is to run new wiring, use the dryer's breaker spot, and install a NEMA 14-50R in the garage.

    - - - Updated - - -

    Oh goody... the engineer's answer: "it depends". This depends upon wire size that comes from the circuit. If the circuit is a 40A circuit, I'm guessing you either have a direct-wire appliance, or a 50A receptacle on it already. As noted you will not be permitted to share the oven circuit - so it will have to be repurposed, so does that mean you'll be reusing existing wiring (just perhaps reversing the box through the garage wall instead of the kitchen or something)? Or will you be running new wiring? If new wiring, just run 6/3 plus ground to the breaker box, replace the breaker with a 50A breaker (they're not too expensive), and install a NEMA 14-50R.

    If you're using existing wiring:

    If the wire is #6 copper, you can replace the breaker with 50A. If you have 3 jacketed conductors plus a bare ground (either via wire or metal conduit), use NEMA 14-50P. if you have 3 jacketed conductors without a bare ground, label the white wire ends with green tape and install a NEMA 6-50P, move the white wire in the panel to the bare bus bar and wrap the end with green tape. If you have 2 jacketed conductors with a bare ground, install a NEMA 6-50P.

    If the wire is #8 copper, you will only be able to install a 30A receptacle even though the wire could handle 40A; this is because NEMA 40A receptacles/plugs aren't readily available. You will be required also to change the breaker to 30A. Like above, 3 jacketed conductors plus bare ground means you can use NEMA 14-30R, otherwise you'll need to use NEMA 6-30R. Keep in mind Tesla doesn't have the adapters for these outlets yet, they are currently supplying standard 120V, NEMA 14-50P, and NEMA 6-50P (to people who have HPWC's on order).

    If the installation is older and uses aluminum wiring, you'll need one size larger (#4 AL instead of #6 CU, #6 AL instead of #8 CU). You'll need receptacles and breakers that are rated for AL wiring too - be sure it says that. Other local codes may apply. When in doubt, hire an electrician.
     
  6. xhawk101

    xhawk101 Active Member

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    My dryer plug in garage turned out to be 50w similar to welding equipment and can be converted to the nema 6-50 plug per the Solar city electrician I had come. He thought the wires were fine. How do you know the gauge # wire? Is it labeled on wire supposedly?

    I got the plug for 7 bucks and plan to switch it myself feeling rather comfortable after his personal visit.

    from my Samsung galaxy s3
     
  7. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Two ways - you can look on the insulation, where it's typically embossed or printed, or you can measure the diameter of the wires (the conductors only, not including insulation).

    #8 is 3.25 mm, #6 is 4.11 mm in diameter.

    If the breaker is already 50A, and you have a 50A receptacle on it, your wire size should be fine. Otherwise you'll need to look at the wire size before determining maximum breaker size you can put on it.
     
  8. xhawk101

    xhawk101 Active Member

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    Great thanks!

    from my Samsung galaxy s3
     
  9. Discoducky

    Discoducky Active Member

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    Thanks, and let me clarify based on your answer. I'd run all new wire and get a new outlet. Your answer is great and I'm just left with one question: Can I keep using the same breaker with a 14-50 or what could I use with the current breaker? I believe I just need to get at least 8 miles/hour of charge.
     
  10. wycolo

    wycolo Active Member

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    > Can I keep using the same breaker with a 14-50 or what could I use with the current breaker?

    I think you should provide for the max amps that the Tesla *could* draw using that charge cable or EVSE charger, rather than relying on manually cutting the charge down x notches from max. You might forget to cut back the charge amps one day, yet the Tesla proceeds with accepting a full charge and things start getting hot. I do not know what car you are charging. Need more specifics.
    --
     
  11. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    You *can*, although I question if it's worth the trouble. If you're pulling new wire to the panel and installing a new receptacle, I'd say just replace the breaker. If you keep the 40A breaker, you will have to manually dial down the charge rate in the car, or you'll end up tripping the breaker and your car won't charge -- you'll walk up to it and it won't be ready for you. You'll need to remember this if you change adapters to plug into 120V somewhere or use a campground service, etc., as the car (currently) does not remember charge rates on a per-location basis.

    You may not use wiring or a receptacle rated for anything less than the breaker size you have (the lone exception being 120V/15A receptacles on a 20A branch circuit) -- so if it's a 40A breaker, the minimum receptacle size you can install is a 50A.

    I don't know your particular panel type, but standard, non-GFI 50A breakers are around $17-18 at Ace Hardware for most common types (BR, CH, HOM, QO). They're a bit more expensive ($50ish) if you need older types (FPE, Zinsco, etc.) It's going to be worth it in the long run to replace the existing breaker, so you don't create confusion about the use of that outlet.

    Just curious -- any reason you want to keep the existing breaker?
     
  12. Discoducky

    Discoducky Active Member

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    I'm worried about maxing out the sub-panel, but I didn't know about the need to tell the car about the reduced Amp *EVERY* time I charge the car. That would be a huge red flag. Do I just add up all the breakers in the sub-panel to see how close I'm at to maxing it out? Also, I don't have access the main panel as I'm in a townhouse and really don't know which main panel services my unit.

    WP_000277.jpg
     
  13. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #13 FlasherZ, Oct 31, 2012
    Last edited: Oct 31, 2012
    You wouldn't have to reset it every time you charge your car -- I think it keeps your charge rate. It's only when you change adapters to the 120V adapter, or if you go somewhere else and use the higher rate. It may even keep your charge rate per adapter type - so a change to the 120V adapter, then a change back to the 14-50 might actually keep your lower rate -- I'm unsure. Either way a $12 breaker removes the need to worry about that.

    To determine a minimum panel requirement, you do a load calculation that the NEC specifies, but in this case you won't need it. Panels inherently have oversubscription built-in -- an additional 10 amps in that panel is unlikely to be an issue. That's a 125-amp panel - likely served with a 100A or 125A breaker from a main distribution panel somewhere. You won't have a safety issue if you upgrade that breaker; if you overload that panel, you will trip the breaker at the main panel. From the circuits I see, even 100A is going to be plenty, even if you're charging at full rate, using your dryer, and running a few other appliances -- the rest is all 125V receptacles and lighting.

    The breaker you need is a Murray MP250 2-pole 50 amp circuit breaker. Amazon sells it for $11.57.
     
  14. sublimaze1

    sublimaze1 8Dec2012 / Leeroy Jenkins

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    Or Square D
     
  15. Lloyd

    Lloyd Active Member

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    You have room for an additional breaker! There is one slot available at the bottom of each row. You don't need to re-purpose your range! Just buy a breaker, move two 1/2 's to the other side and you are good to go!
     
  16. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    #16 FlasherZ, Oct 31, 2012
    Last edited: Oct 31, 2012
    Actually, there are 4 available -- 1 on each side on top and on bottom. The easiest method, should you choose to do this, is to shift all breakers on one side up one slot (so you don't have wire slack problems from trying to move a circuit from one side to another, since the panel is likely to be fed from two raceways), and install the new breaker at the bottom, removing the panel face's two knockouts..

    But that said, if you want simple, simple, simple and you're not using the electric range, then you can just replace that breaker. Cap and label the existing wires, leaving them in the panel for future reconnection, and label the receptacle (if there is one) as "disconnected at panel".

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    Schneider/Square D does not make type MP breakers. They're made by Siemens, and labeled as either Siemens (commercial) or Murray (residential). Square D panels use type QO (compact) or type HOM (Homeline).
     
  17. Lloyd

    Lloyd Active Member

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    Right, I missed the two top slots.
     
  18. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    Slightly off-topic but just a word of warning: never go by the # of blanks in the panel front. I have several panels where the top row and the bottom row have no bus bar connections behind them, so no breakers go there. They're for special things like manual isolation modules and such. You have to go by the diagrams or pull the panel cover and look. The panel diagram in this case shows 8 connections per side, 4 to each leg.
     
  19. Tommy

    Tommy Member

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    #19 Tommy, Oct 31, 2012
    Last edited: Oct 31, 2012
    Here is a spreadsheet to calculate the available ampacity of your panel; there are others on the web, however I found this to be very easy to use. Martin of Tesla provided this to TMC members many years ago. When adding a circuit, it is important that the ampacity of the panel is not exceeded and this will calculate that for you, just need to put in your breaker size for the different types of circuits or if you know the load for a circuit you can fine tune the calculations by entering that info. I have left my panel breakers and appliance particulars in the spreadsheet to aid in putting info in the right spots, just edit/delete the circuits to match what your panel has and if you have room for an additional circuit, you can add that to see if you are under your panel's ampacity. I added a dedicated 240V circuit to my panel and it is shown in the bottom right column. The cals are based on the 2005 NEC code, however I found it is still relevant to today's code.

    View attachment Panel Load Calculation.xls
     
  20. Discoducky

    Discoducky Active Member

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    So, would adding a 50A for the NEMA 14-50R be too much for the sub-panel without repurposing the electric oven breaker? Since it looks like I have room to add the breaker I might just wait to get a gas range:biggrin:

    And thanks very much to everyone who has been helping. I'm going to go to Lowe's this weekend to pick up the breaker, wires and outlet/box. I'll be mounting the outlet right beside the sub-panel in the garage.

    Leviton 279 50 Amp, 125/250 Volt, NEMA 14-50R, 3P, 4W, Flush Mounting Receptacle, Straight Blade, Industrial Grade, Grounding, Side Wired, Steel Strap, Black - Amazon.com
     

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