12 volt DC

System · October 2006

I have a remote cabin that I intend to install four or five light fixtures and switches in. In trying to get information on DC wiring as oposed to AC wiring, I am getting confusing answers. Some are telling me that fixture and switch wiring for DC is different from wiring same for AC. My plan is to utilize a battery pack for 12volt DC. Any advise on wiring switches and fixtures will be greatly appreciated.

niel · October 2006

Re: 12 volt DC

items for use in 12vdc are usually heftier that the ac counterparts. a common ac lightswitch will not handle much power when used in the function of switching dc lights or appliances. there's nothing wrong with using dc lights, switches, etc. when used in the capacity it was designed for. the same thing applies to ac stuff and just stay within the design parameters it was meant for. also do not think because the dc stuff is heavier that it can always be used in an ac capacity as the ac voltages are usually much higher and dc parts may not take it. ac stuff like the light switch is a case that a 15amp 115vac light switch may ony be able to be used for maybe an amp or so because of the arcing dc would generate.
for your dc switches and other componenets these are readily available in automotive stores, radio shack, and even here at naws. you will find that the wire needs to be heavier for the dc stuff because of the lower voltage x the higher current = watts. hope this answers what you had in mind.

Windsun · October 2006

Re: 12 volt DC

Although you can usually use standard AC type wall switches etc, they tend to burn out a lot faster on DC from the heavier loads and arcing you get from DC.

There are a few AC/DC versions available, but you have to look close at the specs to make sure they are rated for both.

Or as Neil said, just go to an auto parts store and use those.

System2 · October 2006

Re: 12 volt DC

Thanks for the reply. I will look online and find the proper switches. What about the actual wiring? Are DC switches and fixtures wired the same as AC? I have had good success following electrical instruction book diagrams for AC but cannot find any for DC wiring.

niel · October 2006

Re: 12 volt DC

the actual wiring will depend on your wants and needs in general, but as to the thickness of the wire needed you can locate and download the pv voltage drop calculator in this section of the forum and use it to help you find out if the wire you're using or want to use is too small.
you can wire the dc stuff in the same as the ac stuff in general, but they are more foregiving from the nec's view on stuff under 50v.

BB. · October 2006

Re: 12 volt DC

Probably a good place for you to start would be with an RV store or website of some sort... You can find energy efficient 12vdc lights and appliances there...

However, a couple points to ponder... You may wish to wire the cabin with ROMEX (14 or 12 awg) wire (good for 15-20 amps) and look for light switches that are rated for 5-10 amps DC at 12vdd. This way, if you ever decide to go 120vac, the wiring is already in-place and properly done.

Next, fixture wise, sometimes you can find standard Edison Base (screw-in bulbs) like CPFL's and a few LED that are available in 12vdc, and all you will have to do later for 120vac is unscrew the old and install the 120vac versions.

Also, you may wish to look at a good RV style AC inverter and just power all of your lights/radios/other lower powered devices with the inverter (place a wall switch for each outlet to allow you to turn off "phantom" loads--like wall worts--while the radios and such are turned off)... Many items, like 12vdc CPFL's and Refrigerators are really AC devices with their own little inverters installed internally. Some of the RV/Cabin inverters can be wired with a generator and will automatically switch between battery and generator line power, and charge the batteries too...

Make sure that you have a DC rated fuse (properly rated) from your battery bank too.

-Bill

Patman3 · November 2006

Re: 12 volt DC

DC has an important polarity, AC you can mess up polarity and get away with it. AC Black wire is HOT, DC black is negative. Try and keep that in mind when wiring.

BB. · November 2006

Re: 12 volt DC

Technically, in the US, AC also has a phase and "grounding" polarity too...

White is Neutral and green/green with yellow tracer/bare-copper is ground (the white and ground are tied at one place in the main panel--so the white is at, or close to, ground potential). Other colors (black, red, and others, are "hot"). Also, improper wiring of the neutral phase in 120/240VAC circuits can cause overheating on the neutral wire (for example, if two "in phase" 120 vac black/red wires share the same neutral, their currents will add--the shared neutral should be with two out of phase 120 vac black/red wires so the currents cancel each other out). [out of phase 120 vac leads will read 240 vac when measured with a meter--in phase 120 vac leads will measure about zero volts]

Improper connections of neutrals and grounds can cause many safety issues.

If I was going to wire using ROMEX or other household wire and standard NEC fixtures/boxes/panels--I would wire the white/neutrals as per NEC, and use a piece of red and black tape at each fixture/connection to indicate polarity (and/or use tags with +/- written on them)... [white would be ground--in a negative grounded system--and the red/black/red-tape connections would be positive]

-Bill

System2 · November 2006

Re: 12 volt DC

BB wrote:

I would wire the white/neutrals as per NEC, and use a piece of red and black tape at each fixture/connection to indicate polarity (and/or use tags with +/- written on them)... [white would be ground--in a negative grounded system--and the red/black/red-tape connections would be positive]
-Bill

After a "lifetime" in electronics, where generally black was negative (ground) I, "knowing I was right" wired a lot of things that way. Only recently did I learn that when it comes to the NEC and standard practices, DC wiring of houses and PV's etc, that black is "hot" just like in AC systems. :oops:
And I thought I knew it all!

Wayne

BB. · November 2006

Re: 12 volt DC

I still get confused by the European Brown/Blue AC line cords... Brown is an earthy color--so was that the neutral in US--or was it the sky blue that was neutral and brown was power....

I have to meter them out every time (the few times I needed to know).

-Bill

niel · November 2006

Re: 12 volt DC

it is true wayne,
sometimes i think they do things like that to confuse people or worse. i too with electronics background assumed black to be the grounded portion as i had wired a replacement ac outlet in an apartment i was in many moons ago. i was questioned by the landlord on the polarity and was promptly corrected. some things are sensitive to this polarity and could blow out or pose a shock hazard when done wrongly. making it different from 2 related electrical fields makes me wonder, what were they thinking?

System2 · November 2006

Re: 12 volt DC

I'm still a little confused but might have it right. If I cable from the battery bank to a breaker box with the + as the black wire and - as the white, the fixtures and switches could be wired the same as with AC. Is that right?

Windsun · November 2006

Re: 12 volt DC

We don't do many DC systems anymore, but now we usually go with red for hot+ - that way no possibility of getting it mixed up with AC.

System2 · November 2006

Re: 12 volt DC

basinman wrote:

the fixtures and switches could be wired the same as with AC. Is that right?

Right !

12 volt DC

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