wire size

ws9876
ws9876 Solar Expert Posts: 448 ✭✭✭
in General Solar Power Topics #1
what size wire is good for a 70 ft run from the inverter(120v) to the mains box. 2500 watt inverter.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: wire size
    ws9876 wrote: »
    what size wire is good for a 70 ft run from the inverter(120v) to the mains box. 2500 watt inverter.

    Well first it has to be able to handle the current, which at maximum power is about 21 Amps. So right away you're at 10 AWG because 12 AWG is rated for 20 Amps continuous (although it would probably work because you'd rarely be at full power).

    Second it has to be able to keep the Voltage drop to a minimum over that distance. If you use 10 AWG at 120 VAC and 21 Amps over 70 feet the V-drop is only 2.5% so again that should be fine. If you substitute 12 AWG the V-drop goes up to 4% which is higher than we'd like to see.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: wire size

    Remember that a "typical" good quality AC inverter can surge ~2x rated current... So if you have heavy starting loads, you may want to go 3 gauges heavier (3 awg = ~2x cross sectional area = 1/2 the resistance). Of course, in smaller wire gauges, they generally go in 2 AWG steps.

    On the other hand, if you have a hard starting load (like a well pump), sometimes the extra resistance helps keep surge currents manageable (higher currents may simply shut down the inverter).

    One way around that would be to run two 12 AWG (or 10 AWG) runs from the inverter... Run your lights/computer/radio/etc. on one branch. Run the well pump/skill saw on the second run. That will help you lesson "brown outs" on your more critical loads while keeping high(er) resistance on the high surge circuit.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #4
    Re: wire size

    I'd say 6 or 8 ga. Needed to reduce loss if you have surges, and you are likely to want to grow the system in 5 years, and 10ga will have to be replaced.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: wire size

    If you trench, drop in several relatively large diameter conduit (I use ABS pipe too)... easy to add/update wiring later.

    Lay two--One for AC wiring, the second for communications cabling later.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: wire size

    Most important: have the right size circuit protection for the wire.

    For example you could use 12 AWG knowing you will never get near the maximum output of the inverter, but it should be on a 20 Amp breaker just in case 'never' happens. That way the breaker trips before the wire fries.
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  • ws9876
    ws9876 Solar Expert Posts: 448 ✭✭✭
    #7
    Re: wire size

    would an Outback have 2 outputs for wires out to a mains??
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: wire size
    ws9876 wrote: »
    would an Outback have 2 outputs for wires out to a mains??

    I don't understand what you're asking.

    Outback inverters have standard 120 VAC wiring for IN and OUT: hot, neutral, and ground.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Re: wire size
    BB. wrote: »
    Remember that a "typical" good quality AC inverter can surge ~2x rated current...
    I don't see where he said it was a battery inverter. If it is, you are correct, but if it's a straight grid tied inverter, it can only deliver its nameplate maximum current.

    EDIT: In post #7 he asked about an Outback.
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