Step 00a.4 — Test the meter before you trust it, and again after¶
Step 4 of 12 · Chapter 00a — Mains safety: read before Chapter 09
(no image — see text)
Parts:
- multimeter with its rated leads · tool
- a known-live wall outlet · tool
Do: Prove the meter live–dead–live before you trust any dead reading, and short the probes to check continuity, leads and battery.
Check
Live–dead–live done once end to end. Probes shorted → beep, near 0 Ω, no dropout when the leads are wiggled. No low-battery symbol.
What you're looking at
The meter, its two test leads, and a wall outlet you know is live. Live–dead–live means proving the meter works immediately before and immediately after the measurement that matters. A dead meter reads no voltage on a live conductor.
A meter that has quietly died reads "no voltage" on a live conductor, which is the most dangerous reading in electrical work. A flat battery or a broken lead does it. Prove the meter on a known-live source, take your measurement, then prove it again on the same source: if it failed in between, you find out before you act on the reading. Do it in this order the first time you use the meter, and every time you are about to touch something you have declared dead:
- Live — AC volts on a wall outlet you know is on. It should read your nominal mains voltage.
- Dead — the measurement you actually care about.
- Live — back to the same outlet. Same reading as step 1.
Then the bench self-tests you will use constantly: on continuity, short the two probes tip to tip — it must beep and read near 0 Ω; wiggle each lead at both ends while it beeps — a dropout is a broken lead. Confirm the battery symbol is not showing. If the meter has a fused current jack, check the fuse now rather than discovering it during a measurement.
Caution
Step 10.17 opens Checkpoint #1 by shorting the probes for exactly this reason. That is the short version of this step; this is the long one, and it is the one to use before you conclude anything is dead.