WiremanWireman · Use a multimeter: volts, ohms, amps: troubleshooting for electricians · 2023 NEC ·
Use a multimeter: volts, ohms, amps
Set up the meter for volts, resistance and continuity, or amps, and read what it tells you.
Before you start
How much electrical experience do you have?
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How it works
A multimeter measures three things, each a different way. Volts are measured across two points (in parallel) on a live circuit. Resistance and continuity use the meter’s own battery, so they’re only done on dead, disconnected parts. Amps have to flow through the meter (in series), which is why the amps jack is fused and why most field current readings are done with a clamp instead.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- What do you need to measure?
- VoltageIs the meter rated for where you’re measuring?
- Yes, the rating covers itTest: Measure voltageExpect: About 120 V hot to neutral (roughly 114–126 V), about 240 V hot to hot on a residential service, near 0 V neutral to ground.
- About the voltage I expectedVoltage present and normal
- 0 VNo voltage, or the meter isn’t reading
- A low, wandering voltage on a wire that should be offGhost (phantom) voltage
- No, or I can’t find a ratingWrong meter for the job
- Yes, the rating covers itTest: Measure voltageExpect: About 120 V hot to neutral (roughly 114–126 V), about 240 V hot to hot on a residential service, near 0 V neutral to ground.
- Resistance or continuityTest: Measure resistance or continuityExpect: Depends on the part: near 0 Ω for a wire, closed switch or good fuse; a steady value for a winding or element; OL for an open switch or good insulation.
- OL (open)Open: no path
- Near 0 Ω or it beepsContinuous: a solid path
- A steady value in betweenA measurable resistance
- Current (amps)How much current are you measuring?
- Building circuits, motors, anything over a few ampsUse a clamp meter for this
- Small control or signal currentTest: Measure current in seriesExpect: The current the device is rated for, like 4 to 20 mA on an analog loop.
- Reads a sensible valueCurrent measured
- Reads 0 and the circuit stopped workingMeter fuse blown, or the circuit wasn’t completed
- VoltageIs the meter rated for where you’re measuring?