making a junction box

System · July 2007

I'm building a home and plan on running 12v through out it, Plugs lights etc everywhere I run 120v wiring. some I will place into service immediately, some for the future. I plan on having 2 or 3 seperate battery banks/solar for different jobs. At the moment in my testing setup I have hooked the wiring directly to the battery posts (with Fuses) I'm thinking that when i go for real I should come from the battery post though a larger fuse into a box that i can hook the Smaller fused wires to going throughout the house. is there a good box for this or should i buy a box, take a 2 heavy copper bars (one for pos the other for neg) drill holes in it and add bolts to hook the wiring to? also I'v heard that some use the reg solid house wire for 12v instead of the multi strand is this acceptable? I use multi strand but find it hard to fine any that is larger then 12 awg /2.

mike95490 · July 2007

Re: making a junction box

I'm glad you are not actually makeing J boxes, but using them to run your 12V wires in.
You should be able to get 10/2 solid romex - rated for 30A
Wire nuts for the gauge you are using should be fine too.

The inspector may want you to paint the DC J boxes some odd color, to prevent them from looking like 120VAC boxes.

Solid or Stranded, they should be equivalent in load capacity. Solid oxidizes less (has less surface area) in the long term.

Please use an oddball outlet to plug stuff into, or else you will find you replace lots of fuses when somebody *will* plug an AC appliance into your DC outlet.

System2 · July 2007

Re: making a junction box

mike90045 wrote: »

I'm glad you are not actually makeing J boxes, but using them to run your 12V wires in.
You should be able to get 10/2 solid romex - rated for 30A
Wire nuts for the gauge you are using should be fine too.

The inspector may want you to paint the DC J boxes some odd color, to prevent them from looking like 120VAC boxes.

Solid or Stranded, they should be equivalent in load capacity. Solid oxidizes less (has less surface area) in the long term.

Please use an oddball outlet to plug stuff into, or else you will find you replace lots of fuses when somebody *will* plug an AC appliance into your DC outlet.

so you are saying that it's fine to use the reg 10/2 house wiring? I thought solid wire had too much resistance. if thats so can I use reg light switches too? also I once heard that the "SQUARE D, QT" circurt breakers were ok for 12v so should i use this instead of fuses? I planned on painting the face plates red with 12v written on it for my plugs and switches if i can use solid wire. the new fussion paint is supose to work on plastic.

niel · July 2007

Re: making a junction box

do make sure you properly size the wire for the required current it must pass and the distance the wire run is with the voltage drop calculator. doing this right the first time prevents you from having to do it again later. oversizing is also a good idea as well as running a few extra wires through, but that's up to you how you wish to do it.
in addition to fuses, you may wish to have it able to be switched in and out of circuit and a disconnect using breakers is the easiest way. http://store.solar-electric.com/fuandbroupo.html you would have to have a master breaker and that would feed the smaller individual breakers for each circuit run.
know that qo circuit breakers work for 12vdc and if you can get an electrical box with them cheaply enough, it'll work fine for distributing 12vdc in your home. maybe check home depot or lowes or even a local electrical supply store to see what is available. if you need to combine circuits you won't have to drill copper bars and tap them yourself as you can get terminal blocks or terminal bus bars to do that. here's an example of the tbb: http://store.solar-electric.com/tbb.html terminal blocks like this too: http://store.solar-electric.com/podibl2x4ci.html
i have to add that not all breakers are rated for dc and in fact few of them are so be careful in selecting breakers for dc.
ps solid wire is easier to work with.

System2 · July 2007

Re: making a junction box

Thanks niel and Mike. back to the planning board for me

mike95490 · July 2007

Re: making a junction box

jayven wrote: »

I thought solid wire had too much resistance. if thats so can I use reg light switches too?

wire is wire

Regular light switches may not handle DC well, it depends how much current you are trying to switch. Less than 1 amp should be OK. (I think)

Vic · July 2007

Re: making a junction box

Hi jay..

Cannot avoid wondering about the utility of having 12 VDC run throughout your house, but you know best. Guess it is not unlike some travel traileres and RV's.

The Outback combiner box -- PSPV, I think, would make a nice DC breaker panel for you. The DC breakers are very invepensive @ abt $10.00 each from N. AZ Wind/Sun.

Also there are some Ham Radio fuse panels designed for running multiple 12 VDC loads, and use ATC style Auto fuses and Anderson Power Pole terminals.
Saratoga Radio 12 VDC fuse panels etc: http://www.saratogaham.com/products.html

Believe West Mountain Radio and a couple of others offer these panels for a small price. Try this: www.westmountainradio.com/HAMintro.htm

Twelve volt systems are at a disadvantage especially when run directly from batteries, as the battery voltage varies widly depending on weather the battery is being charged, the state-of-charge, and of course the drop in the wiring. Depending on your load currents, you may need to spend a lot for large wire for your runs. I assume that your porposed house is going to be fairly small, so the runs might be short.

Good Luck, Vic

System2 · July 2007

Re: making a junction box

Thanks Vic these were what I was looking for as I was setting up my testing 12v system and couldn't find any. now I know where to find it if I decide to stay as I have been doing, But running solid wire and QO circuit breakers may be cheaper if it'll work.
I first started my test with 3,12v fans in my attic and garage ran straight off of a 30w panel then I moved up to pumping my well with 4 LP16 batteries and the trace 3600w/24v inverter and 120v to 240v transformer. charged with 4 solar panels and an air 403 wind gen. then I moved to running house lights, TV, Fans etc straight of 12v. now I'm going to build a small house in the desert 24' X 38'. sold the old house (with well and Garage) now living in old RV on my desert land powered by solar panels. planning on building house from one of those Sutherland Kits. I will have grid power available and a propane tank. but want to make most of free engery as my fixed income will shrink with inflation.

making a junction box

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