12-volt DC Wiring Standardsby David McGuffin
Wiring a 12-volt DC circuit requires a working knowledge of electronics and circuitry. It is important to note that when working on any electrical system, there is an inherent risk of shock and even electrocution. Knowing the standards for wiring a system can help to prevent shorts in the wiring, reducing the overall maintenance required. Usually, a 12-volt system in a home implies the installation of a renewable energy (RE) system such as solar panels.
When wiring a 12-volt system, it is important to use the correct wire size. Typically, 8-gauge American Wire Gauge (AWG) wire is used for a 12-volt system, especially if it is connecting a series of 12-volt batteries for a solar or wind-powered system. The wire gauge is also determined by amperage. Consult a chart such as the one at the Engineering Toolbox website. Incorrect wire gauge could lead to a short or an electrical fire. System inefficiencies increase with greater length of wires and cabling, so it is important for RE systems to use the shortest possible wire lengths.
Connections and Splices
Module connectors for solar panel systems should have a latching design that protects the terminals and can resist exposure to the environment. Junction boxes should be accessible and not welded or fixed permanently to mounting frames. Conducting materials that are spliced together need to be brazed, welded or soldered, with tape used as a final protective covering. Solders that are exposed to the environment should be protected by insulated heat-shrink tubing. Other splicing devices, such as split-bolt connectors or terminal strips also can be used.
Wiring Power Sources
Power source components for a 12-Volt DC circuit can be wired in series or in parallel. Wiring in series will increase system voltage, adding the individual power sources' voltages together. Series circuits have opposing terminals wired together, negative to positive, using 8-gauge wire. Wiring in parallel keeps the voltage the same while increasing the amperage of the system by adding each of the individual power source's amperages together. A parallel circuit is wired by connecting like terminals, positive to positive and negative to negative. A series-parallel circuit utilizes both wiring configurations and creates different amperages and voltages as needed.
The U.S. National Electrical Code (NEC) requires a white or grey wire to act as a grounded neutral conductor for an electrical system. Additionally, the protective ground for a DC cable must be bare, green or green-yellow striped (AllAboutCircuits). The 12-gauge wire commonly used for wiring solar panels to a battery bank utilizes a green wire, which is grounded on the solar panel's frame. Common practice among U.S. electricians and electrical inspectors is that the first active, or hot, wire is black and the second active wire is red.