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Old 03-13-2016, 12:28 PM   #1
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Default Branch circuit wire for a 12v dc off grid solar cabin

Hello all. I have been challenged to wire a cabin that is off grid and solar with a back up genny. I have everything covered except customer wants 12v dc wire ran for the branch circuits in the house. Never heard of that! They insist because it's LED lighting & 12v dc a stranded cable (like speaker wire) will be best. I agree. Stranded will offer more surface for the electrons to flow and will keep loss at a min. But what wire!? I want to run conduit. I don't feel safe putting cl2 rated wire in. The max run will be 50 ft. Not a problem but what Stranded wire should I go with!?
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Old 03-13-2016, 12:32 PM   #2
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If they're running conduit to everything, even with 12 VDC, I think I'd still use #14 THHN.

That way the option still exists to use 120 volts in the future.
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Old 03-13-2016, 12:39 PM   #3
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That's what I said. Their argument was that their are not enough strands or cross section. They want more strands in order to reduce voltage loss. Also the cl2 rated wire is less expensive. I'll post a wire I'm considering. Also, I told them I'm running conduit so if the want to convert to 120vac it can be easily done. They bought that .
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Old 03-13-2016, 12:42 PM   #4
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Something like this...

http://www.monoprice.com/mobile/prod...goryid=1023901
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Old 03-13-2016, 07:25 PM   #5
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Id worry mire about voltage drop then minimum size wire over heating. Not that you should push 50 amps through #14, but at 12 volts even basic lights look attractive on #10.
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Old 03-13-2016, 08:03 PM   #6
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Did you do any actual calculations what the difference in the loss / voltage drop will be with different strand counts, at the distances involved? I bet it's chump change.

I could see doing this with even smaller jacketed cables if the voltage drop is acceptable, but not in conduit. I bet you could do this with 18/2. Save the money and time.

If you're running conduit, the jacketed cable takes up conduit space for no reason, I'd run 14 gauge THHN to keep your options open.
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Old 03-13-2016, 08:06 PM   #7
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What about AWM appliance wire? Like AWM 3321 from Southwire? It has XLPE insulation and is rated for 600 volts. It is fine stranded. I don't see why you couldn't install it in conduit for lighting.
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Old 03-13-2016, 09:14 PM   #8
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What a disaster this will be. DC went out with Edison. Take it from someone who's been off grid for over 20 years. Put in an inverter, a 24 volt battery stack and no DC branch circuits.
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Old 03-13-2016, 09:32 PM   #9
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Quote:
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What a disaster this will be. DC went out with Edison. Take it from someone who's been off grid for over 20 years. Put in an inverter, a 24 volt battery stack and no DC branch circuits.
Nah. Low current efficient electronics are more and more common. DC has no radiative electromagnetic field, so it may be healthier than AC. DC has no capacitive charging and discharging current (not really important outside of transmission, but still real).


20 years ago when your best bet for lighting was fluorescent or incandescent, DC might have sucked. But LEDs have changed all that. By eliminating the middleman (inverter), and using battery voltage for lighting and power, you simplify the system and it becomes more reliable. I imagine the off-grid home of the future will have DC lighting, DC receptacles, and AC receptacles.
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Old 03-13-2016, 11:55 PM   #10
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Nah. Low current efficient electronics are more and more common. DC has no radiative electromagnetic field, so it may be healthier than AC. DC has no capacitive charging and discharging current (not really important outside of transmission, but still real).


20 years ago when your best bet for lighting was fluorescent or incandescent, DC might have sucked. But LEDs have changed all that. By eliminating the middleman (inverter), and using battery voltage for lighting and power, you simplify the system and it becomes more reliable. I imagine the off-grid home of the future will have DC lighting, DC receptacles, and AC receptacles.
Don't hold your breath. Low power DC is waistfull in voltage drop, copper wire sizing, appliances are expensive and choices are limited. I had one DC branch circuit. It was the well pump. $600 SureFlow deep well pump the failed twice, couldn't supply enough pressure and got yanked. I replaced it with a Grundfos soft start pump. Never had a problem since. Now I have zero DC branch circuits. Trust me on this. Go 120 volt AC. After 20 years of living it every day, I have some knowledge in this.
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Old 03-14-2016, 12:09 AM   #11
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http://www.engineeringtoolbox.com/am...uge-d_730.html
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Old 03-16-2016, 02:19 AM   #12
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This is bass ackwards. Skin effect only happens at higher frequency. At DC it is nil.

Besides that skin effect doesn't much care solid or stranded. It is more about the surface of the aggregate conductors. That is why power companies use widely spaced parallel conductors on long distance transmission instead of bundling them together.

Also I agree with the other guy that said stick with AC. I work with a lot of off grid people and the only ones with direct DC anything are those that live in dilapidated shacks or trailers with wires that look like spider webs all over everything.

If you must do DC then just wire it exactly like AC wiring, that way it will be reliable and when you want to change it to proper AC it will be easy.

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That's what I said. Their argument was that their are not enough strands or cross section. They want more strands in order to reduce voltage loss. Also the cl2 rated wire is less expensive. I'll post a wire I'm considering. Also, I told them I'm running conduit so if the want to convert to 120vac it can be easily done. They bought that .
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Old 05-12-2016, 06:42 AM   #13
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are you talking about a main feeder from the battery bank to a DC breaker / fuse panel?

at 50' you'd probably be running 2/0 or 4/0.

2/0 at 12v 100' return is 3% drop at ~40amps
you'd have to figure out you total DC load.

I would defiantly be running all DC lighting. inverters are a power waste and use power 100% of the time even if all lights are off. normally about 3 amps in standby for an avg 2000w inverter.
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Old 05-12-2016, 06:52 AM   #14
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or I think you are talking about branch circuits. do you have a DC panel?

still you need total load on each circuit.

at 50' for a 15a DC load you'd want 6 or 8 awg. 5a 10awg
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Old 05-12-2016, 09:13 AM   #15
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Quote:
Originally Posted by smac999 View Post
are you talking about a main feeder from the battery bank to a DC breaker / fuse panel?

at 50' you'd probably be running 2/0 or 4/0.

2/0 at 12v 100' return is 3% drop at ~40amps
you'd have to figure out you total DC load.

I would defiantly be running all DC lighting. inverters are a power waste and use power 100% of the time even if all lights are off. normally about 3 amps in standby for an avg 2000w inverter.
You're wrong, even my twenty year old inverter has a sleep mode. If no loads are powered, it stops inverting, and pulses my grid looking for a switch closure. All programable for pulse freq and load size. And I would not put in a 2000 watt inverter. That's too small for a whole house. In a system I build, you can have a microwave, toaster, electric freezer and fridg. A well pump, TV... Ect. Like I said, I've been doing this for over twenty years, I know what works.
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