Critical questions about workshop wiring
The right size of wiring
or 240v (left). 12-gauge NM-B, 20-amp
capacity, 120v or 240v (middle).
10-gauge NM-B, 30-amp capacity,
120v or 240v (right).
A: The most common wiring for residential use is non-metallic sheathed cable, called type NM-B, shown in the photos, right. If you run your wiring inside walls, this is your likely choice. In surfacemounted conduit, individual insulated wires are acceptable. Underground feeder cable (type UF-B) looks similar, and gets used in damp areas or for underground burial.
In addition to the right type, you need the correct size, or American wire gauge (AWG), which is dictated by the amperage the wire must carry. The larger the wire number, the smaller the gauge. You can always use heavier-gauge wire than specified, but never use lighter gauge. It may get hot enough to melt the insulation and short out. Color coding used by most manufacturers these days simplifies identification.
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