uneven inverter wire length

jtdiesel65
jtdiesel65 Solar Expert Posts: 242 ✭✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
Any problems with using uneven bat<->inverter wire lengths? I can do 5 ft to the positive side of the inverter, but would like to route the negative side to a box that houses a shunt. So the negative side could be up to 10 ft in total length.

thx
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #2
    Re: uneven inverter wire length

    The only problem with uneven wire lengths (that I can think of) are issues with electro-magnetic radiation.

    Normally, you want your +/- cables running in pairs. This lowers inductance of the cables (a good thing), lowers radio interference (less radio frequency noise), and if you have lightning nearby, less of a chance of the wiring acting like an antenna and "receiving" lightning energy.

    All of these are probably relatively minor issues with a 5 vs 10 foot +/- cable pair and I would not add 5' of cable to "fix" the problem--Unless you see issues (and the cable run of battery to battery is going to be just as much, if not morel, of a "cable routing issue". The additional length of cable just adds to overall cable resistance, which is probably a bigger problem.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #3
    Re: uneven inverter wire length

    I don't think there's any practical problem with uneven wires.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: uneven inverter wire length
    jtdiesel65 wrote: »
    Any problems with using uneven bat<->inverter wire lengths? I can do 5 ft to the positive side of the inverter, but would like to route the negative side to a box that houses a shunt. So the negative side could be up to 10 ft in total length.

    thx

    Uneven lengths of the positive and negative conductors to a single battery is not a problem. Uneven conductor lengths between those feeding parallel batteries is a problem.
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #5
    Re: uneven inverter wire length

    Inverter to battery it does not matter. Only matters when you are feeding parallel loads, like multiple batteries or even something like 2 inverters from same bank.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: uneven inverter wire length

    agreeing with all that has been said thus far do be sure that you account for the extra length for the total length of wire for both + and - in figuring for voltage drops with the wire gauge you are using.
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  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    #7
    Re: uneven inverter wire length

    It's #4/0 AWG sold by the forum's host. Single 24v battery. Dual sw4024 inverters. Each positive on the inverter will be 5ft length directly to the battery post. Each negative from the inverter will be a 5ft length to a 1000amp shunt. And what I was planning to do was to run 2 5ft lengths in parallel from the shunt to the battery.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: uneven inverter wire length
    jtdiesel65 wrote: »
    It's #4/0 AWG sold by the forum's host. Single 24v battery. Dual sw4024 inverters. Each positive on the inverter will be 5ft length directly to the battery post. Each negative from the inverter will be a 5ft length to a 1000amp shunt. And what I was planning to do was to run 2 5ft lengths in parallel from the shunt to the battery.

    Adds up to 15' run of 4/0 AWG. That wire can take 300 Amps, which is 7200 Watts on 24 Volts, much more than the inverter will demand. Current at full power and nominal Voltage is 167. Over that wire length you get about 0.5% V-drop. Nothing to worry about at all.
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  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    #9
    Re: uneven inverter wire length
    jtdiesel65 wrote: »
    Each positive on the inverter will be 5ft length directly to the battery post. Each negative from the inverter will be a 5ft length to a 1000amp shunt.

    Have you thought about adding some sort of disconnect and/or fuse?
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  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    #10
    Re: uneven inverter wire length

    thx.

    Sorry forgot to mention, there's a 250amp breaker for each inverter at the inverter. So the cable goes from the breaker.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #11
    Re: uneven inverter wire length

    Keeping +/- lines taped closely together cuts down on their effective inductance. Wire resistance is not the only bad thing to battery cable runs.

    Inductance of cable runs causes greater over/under-shoot to battery voltage seen by inverter during inverter driver switching and load surges. This causes the filter caps (typically moderately large electrolytic caps) on the inverter battery input terminals within the inverter to have higher ripple current putting more stress on them.
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