12 volt cabin wiring

alberta
alberta Registered Users Posts: 10 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
I am wiring an off-grid cabin for 12 volt lighting (no inspector within 15 miles). The wire will be run inside the walls. What type of wire should I use? Just regular Romex with the appropriate guage, or low voltage 2 conductor (no ground wire), and maybe run it inside conduit in the wall to protect it from nails going through the interior cedar panelling? Do I also need to run a separate ground for the electrical boxes?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #2
    Re: 12 volt cabin wiring

    I would suggest conduit/boxes if you may have problems with "critters" chewing it up.

    You can use Romex/standard house wiring. However, 12 volts is pretty difficult to send much of a distance -- especially if there is significant current involved.

    Using a voltage drop calculator for 14 awg wire, 15 foot one way run, and 10 amps will give you a 0.9 volt drop.

    If you battery is drained to 12.0 volts, with a 0.9 volt drop, that will be 11.1 volts at the load... Many 12 volt loads stop working well around 11-10.5 volts.

    No, you probably do not need to run a separate ground wire. You can get into a bit of an issue running "12 volt car devices" like car stereos, CB's, etc. because the shell of the radio is also the ground return. You can have ground loop issues if you don't have a common ground bus for those type of devices (different "ground voltage because of different voltage drops if not using the same ground return point--if that makes sense).

    If you can use 120 VAC -- A nice sine wave inverter can make wiring even a small cabin a lot easier. They have "search mode" and even a DC "standby" switch to cut standby operation of the inverter to a pretty low level. This is a great little 300 watt (600 watt surge) inverter for $270:

    wind-sun_2112_31323756Morningstar SureSine, 300 Watt Sine Wave Inverter 115VAC

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
    #3
    Re: 12 volt cabin wiring

    Look into MC or BX wire in the guage required for your longest run.
    MC has a ground wire.
    BX uses the metal shielding for the ground.
    If you ever decide to run a generator or any 120 volt system you will already be wired and be able to use the existing wiring.
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #4
    Re: 12 volt cabin wiring

    Back when I was a working electrician, I did a LOT of landscape lighting on estate properties. I would never use less than #12 for low-voltage lighting and if the runs were up over say 30' I would normally move up to #10.

    You could use Romex. You could also use "Malibu type" 12/2 or 10/2 (but that stuff ain't cheap).

    You could use MC or BX and if there are critters around, I might very well do that. You could also use ENT and plastic boxes.

    It were my own personal cabin and I *had* to use low voltage lighting, I would use #12 or #10 BX or MC and metal boxes.

    With low-voltage lighting, you often end up having to do quite a few "home runs" in order to avoid having the lights at the end of the string getting too much voltage drop.

    What sort of lighting were you planning on? If you are planning something like a track light with MR16 lamps and are trying to avoid using transformers then you should be aware that the lowest wattage MR16 is 20w and if you have a few of them they will drain batteries FAST.
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  • alberta
    alberta Registered Users Posts: 10 ✭
    #5
    Re: 12 volt cabin wiring

    Thanks for the replies. I already have a Trace DR 2412 inverter I use for some loads (like running my computer while tying this reply). I already use 12 volt lights- the biggest are 32 watts, in several rooms and bedrooms, all are home run circuits and 12 ga. wire with most about the longest about 35 ft (surprising how quickly the distances add up going up down and around)! And I am addng on, so I'm deciding on whether to mix and match or just go all 110 (which leaves me without lights if the inverter goes), but on the other hand... if I ran 110 I could change my battery bank to 24 volts in the future with no problem-but I could also use a transformer to step down 24 volts to 12 volts and keep the same lights.
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: 12 volt cabin wiring

    Run the Romex you will have " more options" after putting
    it in the wall
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #7
    Re: 12 volt cabin wiring

    "-but I could also use a transformer to step down 24 volts to 12 volts and keep the same lights."

    that would not be possible as those are dc voltages, however, you could use a wall adapter (or power supply) going from 120vac from the inverter to 12vdc to power your 12v lights. a voltage converter is another way to go from 24vdc to 12vdc. an option that i would consider is running heavy gauge wire to a dc subpanel farther away from the batteries that you can run more 12vdc circuits from in the future with smaller gauge wires as it would be too distant from the batteries to carry very many loads through #12 or even #10. the subpanel could also house smaller fuses or circuit breakers for branched circuits while the battery end will have a large fuse or circuit breaker to cover any shorts or overloads on your main run as the smaller ones at the subpanel won't protect that.
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  • System2
    System2 Posts: 6,290 admin
    #8
    Re: 12 volt cabin wiring

    Amazing leds are bright, white and low in wattage.
    12 volt MR16 LEDS are available CHEAP on ebay.com
    Every one I have bought from China has been excellent.
    So many types are available with 75% less power consumption than many standard lamps you may be using.

    example Item #120601530490
    $1.95
    Free shipping
    Base: G4
    Input: DC 12V
    Current: 160mA
    Power:1.9W
    angle: 120°
    color: warm white (2800-3000k)
    Lumen: 70-80 Lm
    Life time: more than 50,000 hours
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #9
    Re: 12 volt cabin wiring

    Have you run any of them for 1,000+ hours yet? Many White LEDs seem to not last nearly the 50,000 hours listed before they go to 1/2 brightness or less (seem to overheat and blacken the interior).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
    Re: 12 volt cabin wiring

    they are also directional and may not be suited for all lighting needs in comparing to cfls. a refrigerator light made of leds may suite very well though if at the right power level and position in the frig.
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #11
    Re: 12 volt cabin wiring

    Run the romex.

    Just remember to ID the plus and the minus with red tape!

    Make sure you also ID the 12 vdc circuits from the 120 vac.

    Running # 12 Romex will carry your average 12 volt loads just fine with out too much drop, assuming you are not running too far.

    Tony
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