ELECTRICAL BASICS · DRILL 1 OF 3
How to read a multimeterPractice on a meter that can’t shock you.
Pick the right setting, plug the leads into the right jacks, then read what the display is telling you. Nine quick steps.
A digital multimeter has three things to get right: the dial setting (what you’re measuring), the jacks (where the leads plug in), and the display (the number, its unit, and symbols like OL or a minus sign). Get one wrong and the reading means nothing, or the meter gets damaged.
Tap your answers on the meter below. If you miss one, you’ll see why and can try again.
Multimeter quick reference
| Dial setting | Measures | Use it for |
|---|---|---|
| V~ (V with a wavy line) | AC volts | Plant power: 480 V, 240 V, 120 V circuits |
| V⎓ (V with a straight line) | DC volts | 24 V DC control power, batteries, sensors |
| mV | Millivolts | Very small signals. 1,000 mV = 1 V |
| Ω | Resistance (ohms) | Coils, fuses, heaters. Power OFF only |
| •))) | Continuity (beeper) | Is there a complete path? Power OFF only |
| A | Current (amps) | Needs the red lead in the A jack and the meter in series. Never across a voltage |
Where the leads go
- Black always goes in COM.
- Red goes in V Ω for volts, ohms and continuity.
- The A jack is only for current. A red lead left in A while measuring voltage is the most dangerous meter mistake: it’s almost a short circuit.
Reading the display
- OL means “over limit”: on ohms or continuity it means open, no path.
- A minus sign on DC means the leads are reversed. The amount is still right.
- 0.0 V only proves a circuit is dead if the meter worked on a known live source before and after (live–dead–live).
On a 480 V wye system, phase to phase reads about 480 V and phase to ground about 277 V.
Common questions
What setting do I use to check 120 V, 240 V or 480 V?
Use AC volts (V with a wavy line, V~). Plant power is alternating current. An auto-ranging meter picks the range for you; on a manual meter, pick a range above the voltage you expect.
What does OL mean on a multimeter?
OL means “over limit”: the value is too big to show. On ohms or continuity it means open, with no complete path (a blown fuse, a broken wire). On a voltage setting it means the voltage is above the selected range.
Where do the red and black leads go?
Black always goes in COM. Red goes in the V Ω jack for volts, ohms and continuity. The A jack is only for measuring current with the meter in series. Never measure voltage with a lead in the A jack.
Why does my meter show a negative voltage?
On DC, a minus sign means the leads are reversed: red is on the negative side. The amount is still right. Swap the leads to read a positive value.
Can I measure resistance on a live circuit?
No. Use ohms and continuity only with the power off and proven dead. A live circuit gives false readings and can damage the meter.
YOUR NEXT STEP
Try it on a real panel
Level 1 puts you at a motor starter panel: lock it out, prove zero energy with the meter, wire the control circuit and run the motor. It's free.
Training practice only. Always follow your site's written energy control procedure, your employer's authorization rules and the meter maker's instructions on real equipment.