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Thread: Wire guage

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  1. #1

    Default Wire guage

    I currently use 12/2 wire for a 3/4 hp submersible pump ran at 490ft if I use a 1hp pump will the 12/2 wire be OK or will this hurt the pump and what will it do if anything?

  2. #2
    Plumber Cass's Avatar
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    Is the 490' to the top of the well head or to the pump? How deep is the well?

    What is the AMP rating of the 1HP pump, I am assuming 240V?

    Personaly For 490' and a 1HP pump I would be using a #10 minimum and most likely I would run #8 to a locking, water proof box with a GFCI receptical in the box near the well head and feed the pump from it. Voltage drop is what you don't want.

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    According to Franklin (the folks that built the motor) they say 400 feet max for 1hp.

    bob...

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    DIY Senior Member tvl's Avatar
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    Quote Originally Posted by cameron
    I currently use 12/2 wire for a 3/4 hp submersible pump ran at 490ft if I use a 1hp pump will the 12/2 wire be OK or will this hurt the pump and what will it do if anything?
    Being an electrician, I will try to help clarify:

    First, the total length of wiring is extremely important (one way). This run begins at the breaker and ends at the pump. You stated you had a run of 490 feet. What you are concerned with is the total voltage drop on the circuit. Normally, you want no more than a 5% volatge drop on a motor circuit.

    If you go to Google and type in Voltage Drop Calculator you will find several good calculators. In your case, a 1 HP submersible pump pulls approximately 9 amps at full load AND a run of 490 feet of #12 wiring will yield approximately a 7% voltage drop. This isn't good! Think of it like this ......... the motor is being starved of energy. So, it isn't good for the motor and most probably will shorten its life.

    Also, I am assuming you are currently using copper wiring. Aluminum wiring would be even worse yet! Bottom line: If you are planning on switching to a 1 HP submersible you need at least #10 copper wiring and that would barely be within tolerance (but, it would be acceptable). Personally, I would most likely choose # 8 copper for piece of mind.

    Excessive voltage drop will also cause the circuit to overheat, which will create annoying breaker trippage. This in itself indicates something is wrong. Hope this is helpful!

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    In the Trades Bob NH's Avatar
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    "Excessive voltage drop will also cause the circuit to overheat, which will create annoying breaker trippage. This in itself indicates something is wrong. "

    Increased heat due to wire losses is distributed along the length of the wire.

    Excessive voltage drop won't cause the breaker to trip unless the current exceeds the capacity of the wire and the breaker. The pump would have to draw 2x its full load amps to trip the breaker.

  6. #6
    DIY Senior Member tvl's Avatar
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    Quote Originally Posted by Bob NH
    "Excessive voltage drop will also cause the circuit to overheat, which will create annoying breaker trippage. This in itself indicates something is wrong. "

    Increased heat due to wire losses is distributed along the length of the wire.

    Excessive voltage drop won't cause the breaker to trip unless the current exceeds the capacity of the wire and the breaker. The pump would have to draw 2x its full load amps to trip the breaker.

    Your statement is true, but I believe that if this individual puts a 1 HP submersible pump on a #12 wire (and I am assuning he is using a 15 Amp breaker) and runs it in the current configuration, he will push the limits of the wiring/breaker, especially with the added voltage drop. However, you're correct. it may not trip the breaker, but the circuit will certainly be pushed to its limits. Just my thoughts!

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