Regulations 2015 NEC regarding 12/24 volts DC, New DC wiring Light/+in my old." I'm Scared "
Jon,

First of all, I want to make a couple of points,


A home owner can do any wiring or electrical on his own home so long as he is not actually tying it into the power grid and he does it up to code.
Most of the codes are common sense so it is really easy if you step back and use your head.
There is no reason to be scared, a system like you are talking about is not too hard and if you have any questions, pretend like you are working with 120vac and you will be fine.
I know that this post looks long but take it chunk by chunk and if anything is unclear then please comment and let me know, I'll be happy too edit it and help you out.


I want to start off by making one distinction. There are many kinds of "current limited circuits" that have very little regulation. These can include communication wires, signaling wires, and equipment like that. It can cause some confusion because these circuits are entirely different than what you are talking about. If you have enough power availability to run lights, then it doesn't qualify as being intrinsically safe.

Articles 720 and 411 of the NEC are the main sections that have the rules specific to these systems but there are a lot of regulation that still applies (I mention some of it below). Article 411 (found here - freenec.com/T254.html) deals specifically with lighting at 30 volts or less. Article 720 found here - freenec.com/T590.html) deals with everything at 50 volts or less.

One interesting thing to consider if you are using batteries is that a 24V bank will normally reach a maximum of 26-28V during a normal charge but during a special charge called an "equalize" charge, it can reach up to 32V.

I am when you are working with any low voltage ( ≤ 30V and ≤ 50V) it falls under the same regulations as high voltage in regard to circuit and wire protection. For example, you need current regulation (breakers, fuses, or advanced circuit protection) because even a "harmless" 12v car battery can provide enough amperage (current) to become a hazard if it gets shorted. 

It also falls under many of the same regulations in regard to grounding. You don't have to ground either leg in DC systems, however, you do need to have a ground wire whenever you string the DC wires. If you don't ground either leg (ie positive and negative), you need too use a DC fuse (or DC breaker) on BOTH legs wherever you need circuit protection. However, if you do ground one leg (you can ground either the positive or the negative) then you MUST NOT use a fuse or breaker on the "grounded conductor" which is the fancy way of saying the grounded leg. Again, you can ground either the positive or the negative but it is much more common to ground the negative line and some DC electronics assume that the negative is grounded and are designed around that assumption. One common mistake that many people do when installing DC systems is that they think that the wiring practices from the automotive industry apply to household DC systems. If unless the negative is not grounded, it is illegal to use a black wire for the negative. This is because the negative is a grounded conductor so the code sees it as the same as the neutral on a normal 120/240 system. A grounded conductor must be white. Also, unless the positive is grounded, it is illegal to use a white wire for the positive.

The difference is that ~30V is the threshold where below that there is virtually no shock hazard and even 50V has very little shock hazard. Notice, shock hazard is very different from arc, short, and fire hazards. So as long as the battery voltage stays below 30V you don't have to worry about making your connections "touch safe" but you do need to make them so that they wont short out. Here is an interesting thread on shock danger. — electronics.stackexchange.com/questions/19103/how-much-voltage-is-dangerous

I don't know where a lot of these codes are or what the specific verbiage is but I studied solar, off grid solar (battery based), and advanced NEC compliance at SEI (Solar Energy International). I am now a "NABCEP Certified PV Installation Professional". I love these kinds of projects so keep me posted!

I hope this helps,

Maxfield Solar