Class 1 circuit?

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powersupplyguy@netzero.ne

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Warner, NH
Greetings,

My wife and I are building off-grid home. Electrician will wire up box and 120v sockets next week. He will place the sockets according to code. Solar panels and 32 deep cycle 12v batteries will be our primary power with LED lighting.

I am not clear on which NEC directives I need to follow. I will be using 12v and 24v wiring through house for LEDs and some 12v outlets for small radios. I could probably get by with Class 2 power level of 100va for everything.

Is following class 2 wiring method a reasonable way yo go.

thank you

powersupplyguy
 
More detail

More detail

Sorry if I wasn't clear.

I would prefer to go from storage battery (with very high available fault currents) to LED fixtures. I have read here on forum of class 2 rated breakers - but I do not have high hopes. Am I forced into Class 1 or something else?

thank you

powersupplyguy
 
Moderator Note:
This borders on DIY but it seems reasonable to discuss the overall classification of the wiring as long as we don't get detailed.

IMO, 725.121 does not list your situation as one that can allow a Class 2 wiring method.

The thread is open for other opinions.
 
Assuming you are planning putting four 12-volt batteries in series for a 48 V nominal battery bank, you'll have eight series strings of batteries in parallel. That is twice what is recommended as a maximum. The more battery strings you put in parallel, the more imbalance you'll have between these strings during charge and discharge cycles. This will cause premature battery failure. You should really increase the amp-hour capacity of your battery (and perhaps decrease the voltage of individual batteries) such that you need fewer (2 to 4) series strings in parallel.

You might want to review this Stand-Alone PV System Design article by Phil Undercuffler at OutBack Power. Phil has lived off-grid and installed a great many off-grid systems. And OutBack Power is a market leader in the inverter market for these applications.

BUILDING A BATTERY BANK

Batteries are available in a staggering range of sizes, styles, capacities and qualities. I find that the most cost-effective solution for most residential applications is specifying high-quality industrial flooded lead acid (FLA) batteries from a reputable manufacturer. For small, budget-constrained systems, I consider golf cart batteries from a reputable manufacturer—but the short-term savings of lower-cost batteries are usually offset by the costs of poor performance and shortened lifespan.

Wiring configuration. Much like modules, batteries are connected in series strings to obtain the desired system voltage. Additional identical strings are added in parallel to increase capacity. Each battery cell provides a nominal 2 V, meaning that for a 48 Vdc nominal system, 24 cells are strung in series.

Unlike modules, there are practical limits to how many battery strings you can connect in parallel. If you think of a string of cells as a chain, then the chain is only as strong as the weakest link. Due to variances in manufacturing, internal resistance and interconnections, as the number of parallel strings increases, so does the likelihood of having a weak link. In this case, the weak link is the one cell that resists charging more than its neighbors. This diverts current through the other strings, leaving the weak string undercharged. To make things worse, an undercharged string not only draws down the performance of the other batteries, but it also continues to weaken unless you take corrective measures.

A battery consisting of a single string of cells theoretically provides the best performance; however, in practice many designers prefer two strings for redundancy. If two strings are used, the failure of a single cell or battery is not debilitating. The system can continue to operate on half the battery capacity while a replacement is on its way. The general industry recommendation is not to exceed three parallel strings. If more capacity is required, you should look at increasing the system voltage or choosing a cell with a greater amp-hour capacity.
Click to expand...

This article about High Capacity Battery Banks is also relevant.
 
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As to you original question, most off-grid residences these days are simply fitted with standard 120Vac wiring. This has been the case for many years now.

Other considerations include whether the appliances will use alternating current (AC) or direct current (DC). All off-the-shelf appliances that can be plugged into a standard wall outlet are AC. For off-grid homes with full-time occupancy, the benefits of AC appliances typically outweigh the benefits of DC appliances. Conventional appliances are readily available, and they run at higher voltages, so you can use smaller, standard AC wiring in your household. In certain applications, such as a system for a small cabin, an RV, or a boat, the greater efficiency created by eliminating the inverter can justify more expensive, harder-to-source DC appliances. For example, a PV system for a boat may run 12 VDC lights, a radio, a TV, and a refrigerator directly from the battery to avoid the need for an inverter.
Click to expand...

Source: Considerations for Off-Grid PV Systems

Also, the best forum for off-grid system design inquiries is here:

http://forum.solar-electric.com/forum
 
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