Low-Z mode, and the voltage that is not there

A modern digital multimeter presents around ten megohms to the circuit. That is deliberate — it avoids loading sensitive electronics. It also means a long conductor running beside a live one acts as one plate of a capacitor and reads a substantial voltage while carrying no useful current at all.

Why it matters

Phantom voltage gets healthy circuits condemned and, worse, gets genuinely live circuits declared dead when someone learns to distrust the meter. Both failure directions are dangerous.

The test

Switch to low-impedance mode — marked LoZ or Low-Z. It drops the input impedance to a few kilohms, which loads the coupling capacitance to nothing. A phantom reading collapses to near zero. A real one barely moves.

Two cautions. Do not use LoZ on electronics: the load is enough to disturb a sensitive circuit. And never treat any meter reading as proof of isolation on its own — prove dead against a known live source, then re-prove your tester afterwards.

Written for Circuit North Electronics — a demonstration store. See the AgenticEcom Suite.