By Chris Deziel
Updated Mar 24, 2022
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Thanks to engineer Nikola Tesla, the first large‑scale power plant at Niagara Falls ushered in the era of alternating current (AC). Because AC reverses direction thousands of times per second, the concepts of “positive” and “negative” terminals no longer apply. Instead, AC devices use a “hot” (live) wire and a “neutral” (return) wire. Identifying which is which is essential for safety and proper appliance function.
AC cords feature a hot and a neutral wire. The neutral is usually marked with a white stripe, ribbing, or white insulation, while the hot wire is unmarked or colored black or red. The larger prong on a polarized plug also connects to the neutral.
Most appliance cords are made of stranded copper conductors wrapped in rubber insulation. One conductor will bear a white stripe or ribbing that indicates the neutral wire; the other is hot. If you can’t see any markings, the cord is likely non‑polarized—a rare case in North America but possible on appliances from other regions.
When you remove the outer sheathing of a cord, you’ll see the individual wires. According to the National Electrical Code, the neutral wire is always white. The hot wire is conventionally black or red. If a third, grounding wire is present, it will be green or bare.
Modern two‑prong plugs are polarized: the prongs are of different sizes, and the larger prong connects to the neutral wire. The smaller prong carries the hot wire. Three‑prong plugs follow the same rule—larger prong neutral, smaller prong hot, and a semi‑rounded ground pin below. If a three‑prong plug has identical prongs, you must inspect the wire insulation to confirm which is neutral.
