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Thread: Wire Gauge Size for 50 Amps

  1. #1
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    Wire Gauge Size for 50 Amps

    Hi,

    After checking out the article here <American wire gauge>, it appears that AWG #6 is sufficient for a 50-amp setup (for NEMA 14-50). However, I recall reading some posts here on TMC saying that it would be better to go bigger (#4, not sure if #5 is common). To my mind, a thicker wire would incur a smaller amount of energy lost to heat (therefore increasing the charging efficiency). Would it be worthwhile to go this route?

    Code:
    AWG#6 - 1.296  mΩ/m
    AWG#5 - 1.028  mΩ/m (21% less than #6)
    AWG#4 - 0.8125 mΩ/m (37% less than #6)
    At 40 A over a wire run of 5 m for 9 hours, total energy lost over the wire run for a 300-mile full charge is:
    for AWG#6: (40 A)^2 x (5 m x 1.296 mΩ/m) x 9 hr = 0.093 kWh
    for AWG#5: (40 A)^2 x (5 m x 1.028 mΩ/m) x 9 hr = 0.074 kWh
    for AWG#4: (40 A)^2 x (5 m x 0.8125 mΩ/m) x 9 hr = 0.059 kWh

    After 300,000 miles, the AWG#4 will have saved around 34 kWh over AWG#6.
    At 0.08 cents/kWh, that's only $2.72, over several years at least.

    So it seems getting a thicker wire will not save money, but it will reduce the temperature of the wire itself during charging.

    I guess my questions are:
    1) How much more expensive is AWG#4 / #5 over AWG#6?
    2) How much cooler will the thicker wire be?

  2. #2
    Senior Member cinergi's Avatar
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    Wow, great question and detail there. I don't know the answers (tho pricing should be easy to find online), but one thing came to mind: some 50A device (the circuit breaker or the plug) might not accept the thicker wire -- so just be sure it does if you decide to go thicker.
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    Model S R77 efusco's Avatar
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    Here's what my installer used:

    Tesla Charger Installation by efusco, on Flickr
    Evan E. Fusco, MD--Nixa, MO
    Model S R77/VIN-1267-- Black 85kWh (non-perf), Tech, Lacewood trim, tan interior, Sound Studio, Air Suspension, 19" rims, twin chargers, HPWC
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  4. #4
    MSP P#1117 teslasguy's Avatar
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    Standard for 50amp is 6 gauge for copper. Use #4 for 100 amp. I'm running 100 amp to subpanel on the garage for future addition of another 50 amp outlet for my wife. For me it cost around $200 extra for the #4 vs #6 for about a 40' run. #4 is much thicker wire to run.


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  5. #5
    Senior Member smorgasbord's Avatar
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    Quote Originally Posted by efusco View Post
    Here's what my installer used:
    Have you had your inspection yet? I don't think 8 gauge wire can be used with a 50 amp breaker.

    The package looks like this: http://www.homedepot.com/buy/southwi...l#.UFENWaTLxZI

  6. #6
    MSP P#1117 teslasguy's Avatar
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    Unless using aluminum wire. I think #8 is ok for aluminum for 50amp.


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  7. #7
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    8/3 NM-B is rated for up to 45A, since the Tesla mobile connector will be drawing 40A maximum, they can get away with it. Yes, technically it's on a 50A breaker.

    See the chart here: Application Charts

    With that said, I used 6/3 NM-B on my 50A 14-50, I'm also using 3AWG THHN for the 75A OpenEVSE I am building on a 100A breaker, because it was less money than 4AWG (believe it or not, $0.75 per foot for the #3 vs $1.20 for the #4)

    600 Volt THHN


    Mitch

  8. #8
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    Quote Originally Posted by teslasguy View Post
    Unless using aluminum wire. I think #8 is ok for aluminum for 50amp.
    Depends on the insulation temperature rating.

    efusco's picture is this product: 125 ft. Black 8-3 Romex NM-B W/G Wire-63949202 at The Home Depot

    If the insulation is rated for 75C, it's good for a 50A circuit. If it's only rated for 60C, it's only good for a 40A circuit.

    Wire ampacity chart: Wire Chart

    The product datasheet indicates that while the insulation is rated for up to 90C temperatures, that comes with the note that ampacities are to be rated at 60C temperatures from NEC.

    http://www.southwire.com/ProductCata...=prodcatsheet6

    So yeah - I'm afraid that efusco's Plug and 100Amp line sticker shock is not yet over - this wire is only good for a 40A circuit which means you can only pull 32A from it with a continuous load like charging your car.

  9. #9
    Senior Member vfx's Avatar
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    A longer run (mine is 180 foot) requires an increased size.

  10. #10
    Model S R77 efusco's Avatar
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    Quote Originally Posted by drees View Post
    Depends on the insulation temperature rating.

    efusco's picture is this product: 125 ft. Black 8-3 Romex NM-B W/G Wire-63949202 at The Home Depot

    If the insulation is rated for 75C, it's good for a 50A circuit. If it's only rated for 60C, it's only good for a 40A circuit.

    Wire ampacity chart: Wire Chart

    The product datasheet indicates that while the insulation is rated for up to 90C temperatures, that comes with the note that ampacities are to be rated at 60C temperatures from NEC.

    http://www.southwire.com/ProductCata...=prodcatsheet6

    So yeah - I'm afraid that efusco's Plug and 100Amp line sticker shock is not yet over - this wire is only good for a 40A circuit which means you can only pull 32A from it with a continuous load like charging your car.
    Well I don't like to hear that! Let me contact the electrician &amp; see what he says.


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    Evan E. Fusco, MD--Nixa, MO
    Model S R77/VIN-1267-- Black 85kWh (non-perf), Tech, Lacewood trim, tan interior, Sound Studio, Air Suspension, 19" rims, twin chargers, HPWC
    Model X Reservation Sequence # 5966 (for the wife)

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