# wiring for future off grid expansion



## kvr28 (Feb 15, 2009)

my wife and I are building a passive solar earth sheltered home and will be converting to solar panels over the next several years, I would like to run any wiring now before I drywall and such, but I can't find any information on gauge of wire for a 12 volt system, any suggestions?


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## zant (Dec 1, 2005)

Depends on how many amps it's carrying...One thing I would do if wiring a house new is-wire for ac and dc....and most important put all circuits in each room on a central switch so you can kill power to that room-be amazed how much electricity is used with nothing on..


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## Jim-mi (May 15, 2002)

You'd be better off in the long run just going with AC.


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## swampyoaks (Jan 6, 2008)

http://www.amazon.com/Photovoltaics...=sr_1_1?ie=UTF8&s=books&qid=1251629371&sr=1-1


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## Windy in Kansas (Jun 16, 2002)

Jim-mi said:


> You'd be better off in the long run just going with AC.


While I don't have anything other than grid service I do agree. The price you pay for specialty appliances, 12 V fixtures, etc. will soon pay for a proper inverter.

Just my opinion that it would be better to stick with conventional wiring.


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## greg273 (Aug 5, 2003)

Going with an inverter is probably the best option, you can keep the existing AC wiring in place, just hook the inverter up to your main panel. For some loads, like well pump or possibly fridge, you may want a seperate DC circuit... but even in that case I would consider NOT going with 12volt, and going instead with a higher voltage. (like 24). This would save you from having to run oversized wiring. 
I have a 24volt water pump that I use to pressurize the house water from a 1000gallon cistern...I have it wired with 30ft of 10gauge Romex...no problems. Actually used to have a 12volt pump on the same wiring, and it too ran just fine, despite drawing twice the Amperage on 12volt. 
BTW, that is one great looking house! Very nice job!


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## roachhill (Jul 8, 2009)

I disagree with using all ac. The inverter involves inefficiency loss and a number of items plugged into the wall are DC they just have converters in line which also involve inefficiency loss. I guess if your going with a large, cost is no object solar system then you can just add panels and batteries to overcome the loss. If on the other hand you are using a small system for limited items DC can save significant power. I'm installing DC for lights, fan, small water pump and laptop. If I need AC i have a 3000 watt inverter. For refridgeration I salvaged a gas fridge from a motorhome. Basically it's the same as wiring a motorhome. High efficiency DC lights can be had without spending more than AC lights a number of DC items are made for motorhomes and semis. Also you can use cigarette lighter plugs and have a small inverter you can plug into them.
As far as ga. of wiring I don't know it off the top of my head but I have a book that explains how to figure it out I just have to go up the hill and dig it out. I'll look it up and post later. Surprisingly few books on solar power get into specifics such as wiring ga. It's important to note you can not use AC rated switches and circuit breakers with DC current they will fuse the contacts.


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## Jim-mi (May 15, 2002)

I have to disagree loudly to the use of cigarette lighter plugs . .!?!?!

It is far to easy to over load them . . .causing great heat . . great heat means Fire.

Running an inverter from a cig lighter plug is just plain a Bad idea.

And those cheap inverters are not worth a powder............

If you can build a place as nice as the pix shows then you can afford to get decent non fire hazard electric equipment to go in it.

When I got a very good 12vdc chest fridge, I ran a dedicated heavy gage wire to it from the power room.
Like wise when I bought my Sun Danzer freezer, I ran a dedicated 24vdc line to it.


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## kvr28 (Feb 15, 2009)

thanks for the feedback, I was going to run most things off a inverter, but was wanting to run for 12v lighting and switch to 12v ceiling fans, so I figured if I buried the wire now, I could just switch over when I was ready, I talked to a local installer and he said for 50,000 he could build me a 5kw system that would run everything, I'd prefer to go with a smaller system

finished painting the house yesterday


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## wy_white_wolf (Oct 14, 2004)

I would consider going with a grid tied system with battery backup for critical loads instead of a full off grid system. 

Doing so will cut down the size of the battery bank needed so it would keep costs down. Also with everywhere pushing time of day (ToD) metering you would be able to cover all your needs with a much smaller array. Simple produce power when the cost is high and use the grid as your bank when power costs are low. Net metering laws are changing to the favor the home owner.

Going this way all critcal loads would be wired into a subpanel of the main breaker box. Access to the cable between them would be needed. Also I'd look into running conduit from where the panels will be located to the invertor/battery area. 

Just for effenciencies sake you most likely will not want a 12 or even 24 volt battery bank or system. I know every seems to worry about the loss from converting DC to AC. But when you look at what it takes to run low volatage DC any distance the losses and cost runs up even faster.

If you do decide you want DC loads you can run that wiring to a second subpanel for now so conversion to DC would be easier for it. If you decide to do this google "wiring loss calculator DC" and you'll find lots of calculators to determine wire sizes. You will need to know length of run (1-way), voltage and amps. You will need to try and keep the loss down to less than 2%. I know others will say 5% but this is only part of the wiring as you will still need to get from the batteries to the subpanel and when it comes to using solar, conservation of resource is key 1.

WWW

PS. Forgot to say nice looking place. I would like to more pictures and details of the design if you don't mind.


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## ||Downhome|| (Jan 12, 2009)

a few things will govern what gauge you use.

length of run,system voltage,system amps,type of wire.

well inverters do have loss, so does a improperly configured dc distrubution systems. loss on a dc run can be very high.lower the volts higher the amps the lower gauge you will need,coppers best for distribution but not cheap either. so I say sit down lay out your needs per room add to 20-30% to your expected needs. figure both ways add the costs. I think you will be really surprised what wire alone will run you.

if it where me I would do a inverter and run for AC. I would also have multiple
circuits per room and have multiple breaker boxs in the long run it would be easier to have multi configurations. 

lighting circuits to one box, appliance loads to another, outlets to another. then if you ever tied into the grid or needed to run a generator you wouldnt need switch gear you can run power right to which ever box you need to. most likely the (appliances washer,dryer,fridge,freezer) 

my friends run alot of stuff at thier cabin off dc though when they do wash 
they fire up the generator well they have the gen running they give the batterys a good charge too, days when the sun isnt producing you might find a system like that to be in your favor. 

you will save in a varity of ways to like not haveing to buy special appliances and cost of heavy wire for the dc circuits,maybe less solar panels.

you can setup your gen to run on a varity of fuels also so it can give you some versitility. 

if you cant tell a generator will be at the heart of my electrical system.


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## farminghandyman (Mar 4, 2005)

if you want the possibility of future
run conduit in the walls and new wire can be pulled in for special or different needs, or make runs to a attic to some general location that can be worked from more easily, 

I think there are things that can be done for "future" needs, 
but the technology is changing so fast, that what was future a few years ago is now obsolete, take wiring for a computer, or a telephone, (in the 70's I worked on a high end house and thousands of feet of wire was ran in the walls for telephones, in ever room including the bath rooms, a few short years later cordless came out and now cell phones),

a few years ago I ran computer wire for a small office hundreds of feet of it so they could interconnect there computers, (I think they never using it and moved to wireless)

currently our church is remodeling the basement of one of the building, when built and for the past 28 years it meet nearly ever need we threw at it, but now some one thinks we need to tear out walls and move things, to one large room, (more than likely in a few short years we will be putting them back in), 

you will have two problems, one the change of technology, (and I think it will be changing fast in renewable here soon), and you do not know what your needs are in the future, you can design and plan for the current use, and may be for some possible expansions, (if you know what your trying to achieve), but if you do not know what what your future needs will be it is very hard to plan for them. 

I worked in a collage for a year as maintance personal, and the school officials keep wanting to change the offices, the rec buildings, and so on there did not seem to be an end in site of the changes they wanted, and when it was said and done few of them improved things, to any great extent, but we keep busy moving walls and wiring and so on, but the simple is you do not know what the future holds and it is hard to plan for it,


I would wire for AC and use an efficient inverter and more than likely go with more than 12 volt system, on the inverter and solar panels


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## roachhill (Jul 8, 2009)

Order a backcopy of Backwoods Home Magazine #116 there's a good article on wiring for a small DC system it covers everything you need. For a larger DC system (which the magazine author doesn't recommend a home owner try) I would recommend The New Solar Electric Home it's an expensive book but it goes into detail on calculating loss and wire ga, ect.
As far as small inverters and cigarette plugs not being safe I've used them successfully for 15yrs. I only use very limited electricity. If your overloading them you probably have to high a power demand for a 12v system. 
Now that were just talking lights and fan DC wiring should be no problem. Just use the NEC guide as long as the distances are under 50 ft over that step up 1 size. The guide says 10 amps 14ga, 15amps 12ga, 20amps 10ga, 30amps 8ga, 60amps 4ga. Also for breakers the square D "QC" line is rated for up to 48v DC as well as AC use.


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## OntarioMan (Feb 11, 2007)

It all makes you wonder if there isn't a better way to wire a house than putting stuff inside the walls. Certainly makes things interesting when trying to update/expand/repair what is in there.

I'd definately wire the house with cat6 network cable, RG59/RG6 TV cable, phone cable, ect. Yup, there is wireless, but a wired network is faster and more reliable. Most data cable is fairly cheap, so unless your house is huge, the cost is fairly low.

Great looking place.


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## roachhill (Jul 8, 2009)

I have a log cabin so very few wires run inside walls. Mostly I built baseboard boxes for everything to run in. When there are changes to be made just open the box. It probably violates some code but so does most of my house. I studied every loophole available to keep inspectors out. It can't be sold this way but I intend to die here so I don't care. I planned everything for easy repair in the future. I don't want to tear out walls when I'm 70 just to fix something.


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## wy_white_wolf (Oct 14, 2004)

Might want to take a look at the charts here:

http://www.windsun.com/Hardware/Wire_Table.htm

Hope the distances you wish to run with aren't very long.


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## TnAndy (Sep 15, 2005)

roachhill said:


> Also for breakers the square D "QC" line is rated for up to 48v DC as well as AC use.



That's QO series Square D, not QC.

And some places I read the UL listing does NOT include 48v DC...47v and down.....point to note if your inspector is sharp.


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## byexample (Aug 28, 2009)

Before setting up 12 volt power systems for your home make sure your understand the concepts involved in "voltage drop". The longer the wires, the greater the voltage drop. When the voltage drops the current required to supply the same amount of power increases... so a 2 amp draw on 3 feet of wire can become 5+ amps on 30 feet of wire. More wire means more current. Fuses become really, really important in a 12 volt setup.

In the end if you want to be safe you have to run really, really big wire for 12 volt circuits if you plan on using 12 volt appliances. And cigarette lighters are not approved for this use. They are rated for 7 amps max!

I agree that there are efficiencies to be had by running loads directly off the DC side of an off-grid power system... but those efficiencies diminish very, very quickly with distance in low-voltage systems. And 12 volt appliances are usually unreasonably expensive compared to their 120V AC counterparts.

In my opinion, 12 volts is appropriate for something the size of a car or RV. Anything larger than an RV and 12 volts requires too large of wires to be practical and safe. You could never run a 12 volt line 100 feet from the house to the barn... but if you are running 120V AC you can easily (and inexpensively) run 300 feet if need be.

My advice to anyone wiring an off-grid house is to wire it like you would if it was going to be connected to the grid. There are lots of books and guides out there for wiring a residence to code... and if you want to avoid problems with building inspectors and / or have the maximum resale value to your home one really should consider wiring it "for real". It also provides a lot of flexibility.

If you shop carefully you can find energy-efficient AC appliances that work just fine on small, off-grid systems.

Be well,

Patrick Harris
http://ByExample.com


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## mightybooboo (Feb 10, 2004)

Excellent post byexample.Looking at that house thats exactly what he should do.

The offgrid paradigm is undergoing rapid change r/t costs,and going more 'conventional' is becoming economically feasible.

Oh,and nice website you have there byexample,look forward to reading it.


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## kvr28 (Feb 15, 2009)

for those that asked about our house, here it is

http://www.mixedmartialarts.com/?go=forum_framed.posts&forum=199&thread=1479494&page=1&pc=409


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