Ground Fault Outlet

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I have a small 12v pump I want to put under my cabin. I want to be able to remove it easily when I leave, so I was planning to use a plug/outlet combination.

Will wiring a GFCI outlet to my 12v circuit panel work or are they inadequate for low-voltage and there something else I should do for safety?

Thanks,
--Tad

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,476 admin
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    Re: Ground Fault Outlet

    A GFI outlet is designed to detect and interrupt AC voltage/current, not DC.

    At best, the GFI may pass 12 VDC, but not ever turn off for any reason (including ground faults).

    At worst, it may not work at all or have other issues (detect a GFI event and arc/melt the internal switch with a DC arc).

    I would suggest a standard outlet--or better yet, something a bit unusual (like a twist lock plug/socket assembly) so somebody does not accidentally plug the pump into 120 VAC or something into the 12 VDC outlet.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Ground Fault Outlet

    Bill,

    Thanks. Actually, I use NEMA 6-20 (250V 20A) plugs and outlets for the 12V stuff in the cabin to avoid just that scenario...someone plugging the wrong thing into the wrong outlet. I would have just wired a ground fault module to one of them.

    So, I shouldn't do anything analogous to "always using ground fault outlets for 120VAC outside"?

    --Tad
  • BB.
    BB. Super Moderators, Administrators Posts: 33,476 admin
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    Re: Ground Fault Outlet

    The GFI is intended to prevent electrocution (line to earth--will not protect against line to line shocks). The GFI works by measuring the "unbalanced" current through the line/neutral connection with an AC current sense transformer connection--any unbalanced current flow is assumed to be returning through an earth ground connection and is possibly an electrocution.

    Generally, anything over 5 mAmps (0.005 amps) is considered potentially dangerous, and over ~15-30 mAmps is potentially fatal if done "properly" (i.e., current flow through the heart--left hand to right foot, left to right hand; but left foot to right foot will not).

    Usually, anything below ~48 VDC is not enough voltage (because of the resistance of human skin) to cause a fatal shock (unless you are wrapped in foil and salt water just right).

    Also, one of the issues with AC vs DC electrocution--With AC shocks, your voluntary mussels contract and you cannot let go (your hand grips the wire/pipe connections). With DC, you get the shock but can release your grip.

    I have received very minor shocks on 24 VDC systems (working on aircraft radio while sitting on a metal rail--thought I was siting on some sort of metal burrs).

    12 VDC--probably not an issue at all.

    Normally people earth ground the negative lead on the battery bank for (help with) lightening protection. If you don't have lightening in your area, floating the DC battery system will actually prevent line/earth faults completely (i.e., an alternative to GFI protection--similar to using an isolation transformer with 120 VAC wiring).

    In the end, I would not worry about the GFI issue at all with any low voltage DC system. Just keep connections clean and insulated so that they don't corrode.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Ground Fault Outlet

    Bill,

    Thanks for the info.

    --Tad