12 volt house wiring

System

Hi everyone I'm an brand new newbie here. I plan on building a house soon. I understand that for 12v to 120v you use a inverter with a sub panel. my problem is for my 12v wiring.as i understand I can use the square D Q? circuit breakers in my 12v breakerbox. my question is what wiring do I use to run from the box to the outlets and 12v fluorescent lights. as i plan on running an outlet and light near every where i put the normal 120v outlets and lights. 1st should the wiring be 2 wire or 3 wire so i have a ground? 2. how big should it be 10 awg, 8 awg or even larger? keep in mind it will be permanent and i don't know what i may use the outlets for in the future. probably i will use 12v coffee pot 12v oven in the kitchen and may use some type 12v heating device in other rooms etc.. who knows what future inventions may bring. 3 what type wire would be best thnn etc? thanks for the info!

mike95490

Re: 12 volt house wiring

I don't know what Code Requirements are (you must follow Code if you want Fire Insurance) but circuit breakers must have a DC voltage rating, not just an AC breaker. Also, for small 12V lights and radios, you are pretty safe, but heating type appliances, that draw a lot of wattage (800W coffee pot), at 12V, will draw 66Amps. That will need a lot of copper wire. For these type of things, you may be better off with a 1,000W inverter, running off a 24 or even a 48 V battery, and use the ordinary house circuit.

BB.

Re: 12 volt house wiring

Sorry Jay,

But I am probably going to ask you more questions than giving of answers...

First, here is a calculator that helps you to calculate wire size vs current. As always, if you are in the US, you also need to run these numbers up against the NEC (National Electric Code) and your local building codes. Again, also use the NEC codes to figure out which type of wires (THNN) and such for your application (based on temperature, humidity, current, conduit vs exposed vs exposed to sun).

http://www.wind-sun.com/smf/index.php?topic=1477.0

Second, there is no one answer for wiring a 12 volt home--there are no standard outlets and no good wiring practices that everyone follows.

So, just some things to think about. In general, solar electric power is expensive to generate and store so you will want to ensure that any electricity you use is done with conservation in mind.

For example, using CFL rather than incandescent lights, low power electronics (laptops vs desktop computers), and few twenty four hour loads (night lights, fans, pumps, computers, printers, radios, tv's, left on when nobody is around (I know--I am probably telling you things you know).

Next, because solar electric power is so expensive (and relatively inefficient)--it is generally not a good idea to use if for any sort of heating applications (for example, solar hot water by solar electric would need 4-5x the roof space and solar PV panels at $5.00 per watt vs solar hot water heaters at closer to $0.50 per watt). Using solar for electric ovens would be a last choice (you are in the middle of no-where and you can afford the solar panels/batteries). Using a microwave is probably OK for a quick heating of previously cooked food.

Next, distribution of power to your various appliances. The wiring calculator above will help you choose the wiring size based on the length of run and current. Generally in solar, folks aim for 3% loss (maybe as high as 5%) of solar power due to wire heating.

Now, the big issue... The reason folks use 120 VAC and 240 VAC to transmit power is because it needs so much less current (and less copper wire) to transmit power efficiently. For example, 12 volts vs 120 volts-- Power is equal to P=V^2 / R... If you use the same piece of wire for both, the amount of energy loss in the wire is (120^2 / 12^2=) 100 times more power loss in the same piece of wire when switching from 120 volts to 12 volts... You would need 100x more copper area to transmit 12 volt power vs 120 volt power.

Another way to think about it--normal home wiring can have a 5 volt drop from the circuit panel to the appliance... But nobody worries about 120-5=115 volts. But take 12 volts - 5 volts = 7 volts and nobody would expect the appliance to even function.

This is all a round about way of saying that when you design a 12 volt power system that you really need to understand where your loads are, where your batteries are, and where the panels will be.

For example, if you do want a 1,000 watt 12 vdc microwave oven--that is close to a 100 amp load. So--it would make sense to install your battery bank next to your kitchen area. And since there are no "standard" 12 VDC connectors--you are going to have to find/select something that works for you. You could choose to use "cigarette lighter" type outlets for loads less than 10 amps--but I find them to be clunky and not very reliable--plus if you have kids around--they are very easy for kids to stick metal objects into cause shorts/fires.

I am sure you have good reasons for wanting 12 vdc power distribution--but I would suggest that you also look into 120 VAC inverters (by the way, pure sine wave inverters are much better--and more expensive--than Modified Sine Wave inverters)--their losses are not that much higher and you would have the ability to use a good range of very energy efficient appliances. People with larger battery banks typically use 24 to 48 VDC because it does reduce the current (1/2 to 1/4 the current and 1/4 to 1/8 heating losses due to wire resistance) and use a 24 or 48 VDC inverter for standard power.

About the only thing to run on 12 VDC are small florescent lamps, automotive type radios and such...

I am at a bit of a loss--it sounds like you are building a home that plans on using a goodly amount of power--but you are trying to use 12 vdc as your power--which indicates more of a cabin or other possible issues (cost of inverters?).

It would be helpful to know your power requirements (watt*hours, kWatt*Hours, or Amp*Hours at what voltage). Just to give you an idea--A hardcore off-grid home probably uses a 100 kWhrs per month... If I try, I can get my old suburban home (near SF California) down below 200 kWhrs per month. Somebody in Arizona with AC--may be 1-2,500 kWhrs per month during summer. And that all still relies on using some sort of fuel/solar hot water/solar heating for heating/hot water/cooking.

Is any of the above helpful for you?

-Bill

System2

Re: 12 volt house wiring

Sorry guys I guess I should explained a little better. I have some solar pannels wind gen and battery pack, Trace 1500w 12v and Trace 3600w 24v Inverters already and I run 12v fans the big one takes 8 watts the smaller ones take about 1/8 amp my 12v coffee pot and oven I'm talking about takes less than 10 amps each, their ones I bought at truck stops. I have a 12v tv/dvd. I will use the 15 or 30 watt RV floresent lights when needed and for small lighting I've found that the newer side marker lights for RV/trucks work pretty good with low amp usage. I'm planning on taking my portable oil filled radiating heater apart (remove the 120v heating coil) and replace it with one of those 300w or 600w 12v water heating coil that farmers use to keep their horse water from freezing, (i know this wont be great but will help with good insulation in the house) with a temp gage it won't run all the time just when the oil cools down. What i'm tring to figure out is when i build my house how to wire it for 12v all over so as things get invented or improved for 12v I wont have to tear holes in the walls tring to upgrade. in other words i'm tring to do it right the first time. sorry i didn't explain better some times i get a one track mind. ps I'm living in my RV now and like having both 120v and 12 volt and think my house should be the same or even 12v better. :-)

niel

Re: 12 volt house wiring

i'll try to simplify the answer for you. you can make this as elaborate as you'd like or as small as you'd like, but it has to have 2 things minimumly. 1> it must be either fused or have a circuit breaker near the battery. 2> it must have wire thick enough to carry up to a maximum current you drsign for it for the length of wire used.
what you use for connections is up to you as long as it can handle the current/voltages you are using and there's no possibility of crossing both dc and ac circuits with a connection that is identical to one another. in other words if you were to use a particular 220vac connection for dc then there should not be any other circuits using that same type connection for 220vac in the place. this is so you or somebody else can't accidentally plug in for example your 12vdc coffee pot to 220vac. i have suggested banana plugs and some like the cigarette lighter type plugs, but for the heavier currents i prefer posts that can be screwed down and tightened. the posts can be bolts with nuts and washers. one thing you might consider is a means of preventing any connections made in reverse. possible switches or disconnects and even small subpanels you may also wish to install. you can plan it out for yourself just as any utility wiring plans would be implemented into a home. the number of connections at what capacity per room if any are up to you.
do use the voltage drop calculator and it is recommended that you keep losses low so the voltage drop percents you'd like to see below 3%, but you could legally go to 5%. remember you are planning for the future too so maybe use pvc raceways to make wire feeds easier and i'd seperate the polarities so that differing polarities wouldn't go through the same pvc raceway. you don't have to do the raceway, but it is an example of what you can do. oversizing wires can help too. use your judgement.

System2

Re: 12 volt house wiring

Thanks everyone! expecially BB & Niel. Niel what are banna plugs with bolt downs do you have a address where i can see a pic? also please don't think i'm too lazy to do the wire calc. I don't have ms word and my net provider restricts my on line time and the most i can get in the time alloted is 80 mbs i have to get a new computer this old 486 just aint doing it anymore.

mike95490

Re: 12 volt house wiring

Banana plugs/jacks : Photos [ I used these in my house, as speaker pre-wire in the wall Jacks on a metal outlet cover (painted white over the galvanized, to match the walls), Plugs on my speaker wires ]

mfg pages:
http://www.keyelco.com/pdfs/p72.pdf
http://www.keyelco.com/pdfs/p73.pdf
http://www.muellerelectric.com/banana_plugs.html

Rated up to about 15A, but some are only 8 amps, read the fine print. You can get them in a Dual Config, with a red & black plug paired together. The Vilcus Plug Dactyloadapter from Think Geek is also a popular item, as as testing tool, but only for higher voltages. http://www.thinkgeek.com/stuff/41/lebedev.shtml

System2

Re: 12 volt house wiring

thanks mike! I kind of like the vilcus plug :evil:

niel

Re: 12 volt house wiring

that is interesting. i wonder why they have finger holes on the other end of the high voltage vilcus banana plug? i'll bet it's great for bad kids too.
here's more examples: http://www.radioshack.com/search/index.jsp?kwCatId=&kw=banana%20plugs&origkw=banana%20plugs&sr=1
i do remember that one banana socket from radio shack had a hole in the post and a screw portion to tie down onto it in addition to accepting the banana style plug allowing more versatility.

System2

Re: 12 volt house wiring

I just had a thought ... maybe Canada or mexico has a different type of wall socket that we can use as a stanard for 12v in the U.S.

niel

Re: 12 volt house wiring

i'm not sure of them, but i believe europe does have different connections.

BB.

Re: 12 volt house wiring

My 2 cents... Wire the 12 volt and 120 volt to different outlet boxes. Do not mix the two in one large outlet... This will help prevent surges from the high voltage side and low voltage side from mixing--and probably reduce radio interference.

Regarding the outlets... I would go find a good 15-20+ amp twist lock outlet (polarized) in your local home center. They will always be handy to replace and get new ones for new appliances. Also, you will have a good selection of cord end and box plugs/outlets/hardware so the installation looks professional and won't raise questions from building inspectors / insurance agents / investigators (in the unlikely event of a fire).

Regarding grounding--you can ground the -12 volt lead of your battery bank. I am not sure that I would bother running a 2 wire + Ground ROMEX to each 12 vdc outlet. In the US, the AC Ground is intended for safety (to pop a fuse or breaker if the hot lead touches the metal case ground in an appliance (drill, toaster, etc.). Since very few 12 VDC appliances have three wire cords and, in the US, most modern 12 volt automotive appliances would have either a plastic case or the metal case already grounded to the 12 volt return--I again would not worry about it. About the only time I could think a third "true ground" wire may help would be if you were using 12 volt automotive radios or transmitters (CB/HAM/etc) where the third ground wire may provide a bit less noise injection into the RF stages--but I am not sure that it would help much (long wiring runs in homes have relatively high impedance and good capacitive/inductive coupling between the three wires in a ROMEX cable).

-Bill

crewzer

Re: 12 volt house wiring

Canada, Mexico, and the US basically share the same voltage, frequency and residential plugs.

See: http://en.wikipedia.org/wiki/List_of_countries_with_mains_power_plugs%2C_voltages_and_frequencies
and: http://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets

The same links contain a lot of info about other countries' voltages, frequencies and residential plug styles. My understanding is that 220-240 VAC is popular because, for a given load, the higher voltage means a lower current, which means smaller gauge wire, which is cheaper and lighter. However, I lived in Europe for many years, and 240 VAC delivers a hell of a kick!  :-(

HTH,
Jim / crewzer