Digital multimeter navigation
CERT 1 · DC/AC Theory & Safety · ~9 min
A digital multimeter (DMM) measures the three Ohm's-Law quantities plus continuity. Voltage is measured in parallel — probes across the two points whose potential difference you want, circuit energized. Resistance and continuity are measured with the circuit de-energized; the meter injects its own small test current.
Current is the trap: an ammeter goes in series, meaning you break the circuit and make the meter part of the path. Measuring current with the probes in the voltage jacks — or across a load — puts the meter's near-zero shunt resistance across a source: a direct short. This is the most common way meters (and fingers) get damaged; it is also a guaranteed exam question.
Clamp meters avoid the series problem by reading the magnetic field around a single conductor — clamp around one conductor only, never the whole cable, or the opposing fields cancel to zero.
Exam focus: parallel vs. series connection, energized vs. de-energized measurement, and the clamp-one-conductor rule.
Quiz — 3 questions
1. To measure current with a standard DMM, the meter is connected:
2. Measuring resistance on an energized circuit will:
3. A clamp meter around a 2-conductor cable (hot + neutral) reads: