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Tips & Guides

Testing low-voltage continuity safely

These exercises use loose AA cells or disconnected, unpowered passive parts only. Do not work on household wiring, mains supplies or high-voltage equipment. Never connect current-mode probes across a battery. Stop if a battery is damaged, leaking or hot.

COM · V/ΩΩ
Continuity: isolated wire, no battery and no power. One probe at each end.
  1. Use only a loose passive wire, switch or resistor, disconnected from every supply and battery. Do not test household wiring or power-supply internals.
  2. Black in COM, red in V/Ω; choose continuity. Touch the probe tips together to check the meter’s response, then put one tip at each end of the isolated wire. A beep usually indicates a low-resistance path.
  3. A disconnected switch should change between open and conducting as you operate it. Beep thresholds differ by meter; OL usually means open or beyond range. Check the manual. Do not use resistance or continuity mode on a battery.

Related explanations

Resistance (Ω)

Official sources