Low Voltage DC Wiring

The finest solar electric components will not function properly if the wire that connects them is not sized and joined properly. Wire that is too small will not deliver the full potential of your PV array. Energy is simply wasted. Undersized inverter cables will not allow your inverter to power heavy loads efficiently. Some high surge loads will not even start due to undersized wire. At low voltage DC, on undersized wire, lights will be dim and TV pictures will distort, and motors will run slower. You will get the same result with bad wire connections, even if the wire is big enough.

At Low-Voltage, every little thing counts for low resistance wiring:

*Solder wire to wire connections whenever possible.
*Make sure mechanical connections are clean and tight. The stripped wire needs to be bright and shiny. If it is an out door connection, lightly grease the contact surfaces with an anti-oxidant (petroleum jelly works).
*If you use solderless connectors, (crimp type) go ahead and solder them after they are crimped on the wire.
*Use #10 gauge or larger for house wiring (especially for 12 volt systems).
*Don't put several loads on the same circuit. Run individual circuits when possible.
*Fuse every circuit in the system. Size fuses according to the ampacity of the smallest wire in the circuit.
*AII switches go on the positive leg to the load.
*Get acquainted with the wire charts.

WHAT KIND OF WIRE TO USE?

For house wiring at 120VAC, regular #12-2 NEMA romex (or non-metallic sheathed cable) is sufficient. It will work fine for some DC wiring that is close to the battery. #10-2 and #8- 2 romex will work for most low voltage DC household appliances.

Type USE wire is good for outdoor use; it can be buried or out in the open. It is also good for house wiring. #10 USE single conductor is good wire for interconnecting solar modules.

For long outdoor runs (from the PV array to batteries, or to bring DC power to another building, aluminum cable type UF or USE is an economical way to make long runs with big wire (#4 to 4/0 AWG). For extra protection it never hurts to put cable in conduit. Do not use aluminum wire for indoor circuits. To connect copper and aluminum you have to use a special split bolt connector to prevent oxidation between dissimilar metals. As a general rule, to substitute aluminum cable for copper, use at least the next larger size.

Large inverters 1500 watt and up will require big copper wire. The most preferable type is welding cable. Because of its fine strands, it is very flexible and easy to work with. It also has a thick rubber insulation, which makes it safe for open air applications. Welding cable is available in #4 to 4/0 sizes.

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