How do I use a multimeter to check for power?

I need to check that power going from my light switch, to a light fixture on the same wall, as well as a light fixture on the opposite wall. How do I use a multimeter to do that?

• Could you edit the question to be a bit clearer as to what is happening? What happens when you flip each switch? When did this start? – bib Mar 2 '16 at 12:28

WARNING

If you're not comfortable working on live wiring, please contact a local licensed electrician. Working on live wiring can be dangerous, and could lead to property damage/loss, personal injury, and/or death.

To test voltage, you'll want to set the meter to the "Volts AC" setting. On the meter it will likely look like a capital "V" followed by a "~".

Typically there will be more than one setting within the range, so you'll want to choose the setting that is higher than what you expect to get. For example. In the US a lighting circuit is typically 120 volts, so you would choose the "200" setting typically found on most meters.

Check the documentation for the meter you're using, to determine where each probe should be plugged in. Typically the black probe goes in "COM", while the red goes in "VΩmA", "VΩ", or "V".

Carefully touch one probe to a known good ground, and the other to the "hot" conductor. (When I say "ground", I don't mean dirt. I'm talking about electrical ground). Next with the one probe still touching ground, touch the other probe to the "neutral" conductor. (When I say touch the conductor, I mean touch an exposed part of the conductor with the tip of the probe. Touching the probe to the insulation on the wire, isn't going to do anything). Finally, touch one probe to the "hot" conductor, and the other to the "neutral".

When you measure between ground or "neutral" and "hot", you should measure line voltage (about 120 volts). When you measure between ground and "neutral", you should measure 0 volts.

How do I use a multimeter to do that?

First

• Marked as Cat II rated, credibly so?
• Probes and leads marked for an AC voltage greater than your supply?
• Good-sized finger-stops on the probes
• Probe-tip shrouds to prevent shorts (or fingers reaching metal)
• HRC fused?

But

• Measure a genuine 120VAC (or 230VAC) source and check the meter shows the correct reading for a live and dangerous condition.
• Turn off the supply to the circuit you are working on and check for 0V.
• Before touching anything, go and check a live circuit elsewhere to be sure your meter didn't coincidentally die between the previous steps.

The last step is a bit overkill, but better safe than sorry.

I generally don't recommend using multi-meters to the uninitiated, 120V is pretty painful and you need a healthy concern for your own safety when working around exposed wiring. Most people I find aren't scared enough until they get shocked and that could be too late.

In all honesty, You really don't need a multi-meter, a non-contact voltage detector is easier to use, and hands down safer since you don't have to have exposed wiring. they cost between \$10 and \$20 and should be in your pocket when doing electrical work.

The use is simple. First make sure it works right. Find a live working outlet, place the probe end near the smaller opening for the plug, that's the hot side. the probe should light up and make a noise. You don't need to touch anything, just get with in an inch or so.

Now that you know it works, turn your switch on, use the probe to check for power at it, then go to each light and test for power. Get as close to the bulb base as you can, with in 1 inch usually is close enough.

• 1" is rarely close enough for the one I use, you need to be on the correct side of the romex cable, or with the plastic tip inside the hot side of the outlet. – BMitch Mar 2 '16 at 21:04

When using a meter on a live circuit you would use the volts AC and select a range that is higher than what you expect 120V standard outlet herein the U.S. 220v across the Pond. If auto range select the correct function and make sure leads are in the correct locations on the meter. If you have the power off and want to verify continuity you would use the ohms setting at the lowest value. (using a ohmmeter on a live circuit will let the magic smoke out).

if you don't know how to use a multimeter, you don't understand even rudimentary circuits.

you should not be messing with anything electrical. call an electrician.

not trying to be rude, but the magic wall pixies in electrical doodads can in fact kill you. nobody wants that.

• I disagree. I had a firm grasp on electrical wiring, circuits, and micro controllers before I knew how to "properly" use a multimeter. – DarthCaniac Mar 2 '16 at 18:44
• i am not sure if "properly" is even a concern here. if you can't figure out voltage across line and neutral or line and ground in an ac installation, you shouldn't be touching them. – personal privacy advocate Mar 3 '16 at 1:41