If you’re having trouble with your electrical outlets or want to make sure they’re working properly, a multimeter is a quick and easy way to test them; it’s perfect for checking for issues like faulty outlets or loose connections.
In this guide, ill show you how to check your outlets with a multimeter, so you can make sure your electrical system is safe and working.
You can check an outlet for three things with a multimeter. Power, Grounding, and Polarity.
First, set it to measure AC voltage. Then check:
- Whether power reaches the outlet by doing a POWER TEST – Insert the probes into the two vertical slots (in any order). Getting a reading close to 110-120 volts would be best.
- Whether the outlet is grounded by doing a GROUNDING TEST – Insert the black probe into the ground slot. You should get the same reading.
- Whether the wiring is proper or reversed by doing a POLARITY TEST – Insert the red probe into the small vertical slot and the black one into the longer slot.
Using a multimeter to conduct these three tests will give you more precise readings than using a current tester.
I will go into more detail below.
Checking an Outlet with a Multimeter
You will need a multimeter to check any outlet. Either an analog or digital type will do.
Safety Precautions
Safety precautions below are very important because you will test the power outlet while it is live.
While checking a live outlet with a multimeter, never touch the metal prong on the end of each probe. You can also hold both probes with one hand so that the current does not pass through your body in the event of a shock.
Checking an Outlet for Power
We will conduct a POWER TEST to check an outlet for power with a multimeter.
Step 1: Set the Multimeter
Firstly, set the multimeter to measure AC voltage.
It might be marked with a wavy line. If there is more than one option, the one you choose should cover the range of up to 120 or 240 volts, as per your main voltage supply.
Plug the multimeter’s red probe into the jack marked ‘V’ for voltage (or a + or omega sign) and the black probe into the multimeter’s common jack marked ‘COM’ (with a minus sign).
Step 2: Insert the Probes
Insert the multimeter’s two probes into the receptacle’s slots (for line/hot and neutral).
Because it’s AC voltage, it doesn’t matter which probe goes into which slot. The two thin vertical slots are shown below as ‘hot’ and ‘neutral.’ The shorter one is for the hot connection, and the longer one is for the neutral one.
If you want to match the probes to the slots, the red one will go into the short slot and the black one into the longer one. But as I said, you can also test it the other way around.
The third-rounder slot is for the ground connection. Note that all three slots can potentially have current, so you should treat them all cautiously.
Step 3: Check the Reading
With both probes inserted into the outlet’s slots (line and neutral, in either of the two possible ways), check the reading on the multimeter.
If power is present in the outlet, you should see a reading. If it’s an analog multimeter, the dial will rotate; if it’s a digital multimeter, you should get a numerical reading. A normal reading will show a value close to the voltage rating of your main electricity supply (usually 110-120 volts in a single-phase US home).
What if There is No Power?
If the dial does not move at all, hardly moves a little, or the number is very low (0-2 volts), the outlet has no power. The circuit breaker might be tripped, or the wiring might have a problem.
If you fix or replace the outlet, it is safe to proceed. However, you should ensure the circuit breaker is off for that outlet before opening it. Confirm again after removing the faceplate that there is indeed no power.
You can test by touching the probes directly to the wires and terminals inside.
Checking if an Outlet is Properly Grounded
We will conduct a GROUNDING TEST to check an outlet for proper grounding with a multimeter.
Method and Expected Result
To do this, keep the red probe in the outlet’s small slot and put the black one into the ground slot (the rounded, U-shaped one) or a metallic part of the fixture.
When you do this, the reading should not change. It should remain the same.
What if the Outlet is Not Properly Grounded?
If the reading doesn’t remain the same, the outlet is not properly grounded.
Also, there should be no current on the outside of the outlet.
The casing is a potential hazard if you get a reading greater than 0.001 volts. You will have to open the outlet (after turning the power off) and ensure it is properly grounded.
Checking if the Wiring is Proper or Reversed
To check an outlet for proper wiring with a multimeter, i.e., whether the live and neutral wires are connected to their respective terminals or reversed, we will conduct a POLARITY TEST.
Method and Expected Result
To do this, insert the red probe into the long slot (normally meant for neutral) and the black one into the short one (normally meant for hot).
You shouldn’t get a reading.
What if the Wiring is Reversed?
If this reverse arrangement gives you a reading, it will confirm that the wiring is reversed.
However, this is not something you need to worry about. That’s why I said above that you could also check for power in this reversed way. Most household appliances will not be affected and will continue to work normally.
A reversal only matters if you’re using a sophisticated device or doing electronics testing requiring one specific AC direction.
Reference
Black & Decker. The Complete Guide to Wiring: Upgrade Your Main Service Panel – Discover the Latest Wiring Products – Complies with 2008 NEC. Black & Decker Complete Guide. Editors of Creative Publishing International. Cool Springs Press. 2008.
Video Reference
AMRE Supply