In-Line Disconnect question

SolarSailor
SolarSailor Solar Expert Posts: 49 ✭
in Solar Beginners Corner #1
If one were to place an in-line disconnect from a 12V battery, onto which cable would it be attached. Something from my old electrical knowledge database (ha!) has me recalling this needing to be the ground leg and not the positive leg.

Can someone confirm?

TIA
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #2
    Re: In-Line Disconnect question

    If this is a neg grounded system, then put the disconnect on the positive leg. That way there is no Pos to gnd voltage past the disconnect assuming that there are other circuits on the system to the battery.
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  • SolarSailor
    SolarSailor Solar Expert Posts: 49 ✭
    #3
    Re: In-Line Disconnect question

    Thanks MikeO,

    I guess that makes sense because some/most devices have their own ground.

    FWIW, and really, this is for the auto, but was planning to use solar hardware for it. A 12-volt system is a 12-volt system as I see it, and the solar hardware is higher quality and sometimes even less pricey.

    Think I may be recalling house wiring where the ground is switched on a light circuit. Or, maybe I'm just remembering wrong all together.

    Anyway, thanks.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #4
    Re: In-Line Disconnect question

    Not entirely wrong... For negative ground cars/vehicles, "they" tell you to disconnect the ground lead of the battery first.

    Disconnecting the ground first means that if you hit anything with the wrench/pliers while unbolting the ground connections--That you cannot cause any sparks because the wrench and the ground are at the same potential.

    Once the ground has been disconnected, then you can start removing the positive post safely, because there is now no way to create a short powered by the battery (since the ground is already disconnected).

    For NEC/Home wiring, they want every thing to either be at ground (neutral, ground wire, metal cabinets, etc.) that can be touched by an end user (again, no shocks or sparks).

    Any "hot wire" that fails and come in contact with any metal will not energize the metal, but instead cause a short to ground which will "pop" the fuse/breaker for that specific hot lead.

    If you had ungrounded metal (say your sink faucet) and it got a connection with with a hot wire--then the next time you touched the faucet and had a hand in the sink/sink water--you could get a shock through your heart because of the grounded sink/sink drain.

    In general, you never "switch ground or neutral connections" only "hot connections" for safety--Neutral/ground is always "touch safe" and hot wires are de-energized when a switch is open or fuse/breaker is tripped.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SolarSailor
    SolarSailor Solar Expert Posts: 49 ✭
    #5
    Re: In-Line Disconnect question

    So, I should always disconnect the ground first, but still put the switch on the positive lead, as I understand what you said.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,641 admin
    #6
    Re: In-Line Disconnect question

    If you are working on a battery (battery bank) that is in a grounded metal box / near grounded metal cabinets that could be touched with the wrench used to disconnect the battery leads--yes, you should disconnect the ground first.

    Also, you should wrap your wrench/tools with electrical tape to prevent accidental touching/shorting while working on the battery bank.

    If this is in a fiberglass boat (no ground metal nearby)--then it probably does not matter too much which to disconnect first.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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