DC only in residential cabin

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strugglinsparky

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Fort Collins, CO
I have a customer who has DC lighting in a cabin. It is a remote area of Colorado. He currently hooks up a single portable battery, but will eventually want to get solar power. He the place brought up to current code. With solar we would use an inverter to change from DC to AC and would run everything with AC. For now the only source is a DC battery. I believe by code I would need two separate panels,with separate sec's, one for the lighting for DC and one for power AC, hooked up after an inverter, fed from the battery. Is this correct? I think I should just change the lighting to AC and feed a single panel from a inverter, that could be used later for the pv system. With only one battery being used as our source, he wouldn't be able to run lighting for any length of time with a inverter to AC Thank you for any knowledge you can share with me.
 
I thought there was a struggle at one point that building depts were not giving CofO's to the Amish houses without at least a 100A service preventing them from living there.
 
If the Amish bore grudges, the AHJ would be smarting from a court-order spanking. People in the US have lived without power for non-religious reasons since the founding. Add religious issues and I can not imagine that any Federal Judge would let such go by.
 
The lighting is currently D/C. The receptacles are currently inteconnected with them. They are your standard 115v duplex receptacles. Which I would need to find, then install some sort of D/C wall receptacle. Another reason I know realize after reading article 720 is that, the current wire's are 2 #12/2 feeding the kitchen circuit. Which I would need to replace with 10 AWG. He is off the grid, but I need a key code to get through the gate for the subdivision!:huh:
 
strugglinsparky said:
The lighting is currently D/C. The receptacles are currently interconnected with them. They are your standard 115v duplex receptacles. Which I would need to find, then install some sort of D/C wall receptacle. Another reason I know realize after reading article 720 is that, the current wire's are 2 #12/2 feeding the kitchen circuit. Which I would need to replace with 10 AWG. He is off the grid, but I need a key code to get through the gate for the subdivision!:huh:
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Well with this I can see you have violations, 120 volt receptacles are not listed for 12 volt use there are receptacles for 12 volt use, many use common lighter sockets, while some chose those small two pole twist lock types.
Another couple problems that is over looked on low voltage installs is voltage drop and proper protection of conductors, many don't realize that a 100 watt lamp might only pull .9 amps at 120 volts but a 12 volt 100 watt lamp will be 9 amps, it don't take many loads to drive a circuit over its limit, as for voltage drop, while we might accept a 6 volt drop at 120 volts, at 12 volts that is half of the available voltage, so again much larger conductors have to be run, also connections are very subject to bad connections, it doesn't take very much to loose a connection at 12 volts that would otherwise work fine at 120 volts.

I did a hunting shack that all they wanted was a few lights and to run a radio and a very small refrigerator, we chose CFL's because of the much higher lumen's per watt, and a propane RV refrigerator that would run 120/12 volt, all the lighting was fed from a small 400 watt inverter as well as the plug for the radio or small TV, and the propane refrigerator was left in the 12 volt mode, they used 3 27F deep cycle marine type batteries, and could charge then from their vehicle or if they brought out a generator they had a hook up and small transfer switch to switch every thing off the inverter to the generator, while the generator would also charge the batteries, it turned out nice.
 
I once retrofitted some lighting fixtures wth automotive sockets/lamps for a cabin in Mexico. Worked great!

DC seems like the way to go for LED lighting as well as a lot of electronics. Cook and heat with something else and you are good to go.

To have both systems installed I'm thinking two completely separate systems.
 
strugglinsparky said:
With only one battery being used as our source, he wouldn't be able to run lighting for any length of time with a inverter to AC Thank you for any knowledge you can share with me.
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The light will run just a long with an inverter to AC as it would hooked directly to DC. Power is power. What you want to find is low wattage lamps that produce the most light and right now those are either CFL ( cheaper) or LED ( more expensive).

If they want more power what they need are more batteries and a power source to charge them, either a generator or solar.

I have been talking to a guy with a small cabin in Kentucky and he has gone with solar and that sounds like the best option. He has few panels that he built himself to save money but already has a small A/C unit that he can run to cool things off at night.

It's all a question of what they want and how much they want to spend.

I did some calculations and I think solar panels will pay for themselves when we compare them to the cost of charging with a generator and gas at almost $4 a gallon.
 
strugglinsparky said:
If he decides to stay with d/c power, would the minimum requirements for receptacles in a dwelling still apply?
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210.52 Dwelling Unit Receptacle Outlets.
This section provides requirements for 125-volt, 15- and 20-ampere receptacle outlets....
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If you were to run the two required small appliance branch circuits but did not have 125 volt to supply them with just what purpose will they serve? A 1500VA circuit @ 12 volts will need 125 amp conductors. I don't know where you will find many appliances to use here that will have same output capacity as their 125 volt counterparts.

If there is not 125 volt available I don't see why you should have to comply. If you are planning to install wiring because someday there may be either a service or more reliable source I would install the required circuits anyway so you are covered when the time comes.

The question is whether or not the place is subject to electrical inspection, and if it is what the AHJ will require if not supplied by an AC source. Around here if it is not supplied by utility service it wouldn't have to have an electrical permit. If other building permits are required, they come from other entities and are not related in any way.
 
Open Neutral said:
What regulation even applies to 14/28 VDC battery systems?
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90.2 seem to indicate that NEC does apply. Most of 210 requirements are pretty clear that they apply to 120 volt circuits. If NEC applies to the dwelling then I don't see how you can get by without the required outlets in 210 - and they must be 120 volts.
 
I'm supprised nobody has brought up that most residental grade switches are not rated for DC, DC has a hotter arc and will shorten the life of the switch. AC/DC switches are available though, usually commercial grade.
 
hillbilly1 said:
I'm surprised nobody has brought up that most residential grade switches are not rated for DC, DC has a hotter arc and will shorten the life of the switch. AC/DC switches are available though, usually commercial grade.
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You have to understand how contacts handle current and voltage to understand how it interrupts the current, inductive loads are the most damaging to contacts and have the lowest current rating for the same contacts, resistive loads do not have this problem as much and this is why we see higher contact ratings for this reason, the different between AC and DC is nothing more then the odds of operation at the zero crossing of the AC sine wive, DC will always have current when opened and will always arc while a certain percentage of opening a switch on a AC circuit will depend upon how many times it is opened at the zero crossing, yes its a gamble, but one played by manufactures in the rating of their switches.

The biggest problem for contacts is voltage, this is why most contacts have a higher rating for lower voltages (look at any relay), this is because the arc extinguish much faster then in higher voltages, while the problem of higher current present in lower voltage circuits will be a problem and the fact most snap switches will not have a DC rating on them, if used for the same amperages they are rated for will most likely last much longer at lower voltages, as far as DC goes, they only thing that adds to the arc is there is always current flowing when the switch is opened, no opening at zero crossing to add to the life of the switch, but I think the added life of being operated at 12 volts would offset this.
 
hurk27 said:
You have to understand how contacts handle current and voltage to understand how it interrupts the current, inductive loads are the most damaging to contacts and have the lowest current rating for the same contacts, resistive loads do not have this problem as much and this is why we see higher contact ratings for this reason, the different between AC and DC is nothing more then the odds of operation at the zero crossing of the AC sine wive, DC will always have current when opened and will always arc while a certain percentage of opening a switch on a AC circuit will depend upon how many times it is opened at the zero crossing, yes its a gamble, but one played by manufactures in the rating of their switches.

The biggest problem for contacts is voltage, this is why most contacts have a higher rating for lower voltages (look at any relay), this is because the arc extinguish much faster then in higher voltages, while the problem of higher current present in lower voltage circuits will be a problem and the fact most snap switches will not have a DC rating on them, if used for the same amperages they are rated for will most likely last much longer at lower voltages, as far as DC goes, they only thing that adds to the arc is there is always current flowing when the switch is opened, no opening at zero crossing to add to the life of the switch, but I think the added life of being operated at 12 volts would offset this.
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As I said, hotter Arc because current is constant.:)
 
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