Yet another grounding question...

Hi all,

I have one more question about grounding...Can anyone explain the reasoning behind the NEC requiring your equipment grounding conductor to increase proportionally in size to oversized current carrying conductors?

I have a 1100 Watt inverter that will have 2/0 welding cable running to it from the batteries. It would normally require only a 6awg conductor, but I oversized it. Does that mean I need a 2/0 grounding conductor just for the inverter's equipment ground? This doesn't make sense to me.

What would be the minimum size equipment grounding conductor I could use in this instance?


  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    Re: Yet another grounding question...

    I am not an electrician--but the sizing of the grounding conductor in the equipment I designed was to be large enough to trip the up stream circuit protection device...

    So, if you have a 15 amp breaker and a 0000 welding cable, you would not need to up size past the standard 14 awg wire.

    HOWEVER, if you had very long run and you installed 0000 to reduce voltage drop--At least I had to work out what was needed to both handle the over current and have low enough voltage drop to trip the breaker (i.e., a very long 14 awg wire would have too high a resistance to reliably trip the circuit breaker--so the ground would need to be scaled larger).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • czyhorseczyhorse Solar Expert Posts: 42 ✭✭
    Re: Yet another grounding question...

    Since the breaker between my inverter and battery bank is 125A, then according to 250.122 of the NEC I would be required to use 8awg for the equipment grounding conductor? Is this correct?

  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Yet another grounding question...

    According to that table, #8 is good for *up to* 100a. Since you are using a 125a over-current device, you would need to move up to the next size - #6 if using cu, or #4 if using al.
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