This article shows you how to test a power outlet in your home with a multimeter.
You can check an outlet for three things with a multimeter: a power test to see whether power is reaching the outlet, a grounding test to see whether the outlet is grounded, and a test to see whether the wiring is reversed. You can do these tests using a current tester, but a multimeter will give exact readings.
- After turning the power to the outlet off and setting the multimeter to measure AC voltage to test for power,
- Insert the red and black probes of the multimeter into the two vertical slots in any order.
- If your main supply voltage is 120 volts, you should get a reading close to this.
- We insert the black probe into the rounded ground slot for the grounding test, which should not change the reading if the outlet is properly grounded.
- The reversal test is only necessary if you have specialized equipment that requires one specific direction.
I will show you in detail, with illustrations, how to conduct these tests to check an outlet.
Testing an Outlet Using a Multimeter
What Can We Test on an Outlet?
Using a multimeter, we can usefully test for the following things on an outlet:
- Whether power is reaching the outlet or not
- Whether the power outlet is properly grounded
- Whether the wiring inside the outlet is proper or reversed
In this article, I will show you how to do all the above three types of tests.
Although you can use a simple current tester for these tests, a multimeter will give you exact voltage readings.
You will need the following:
- Multimeter (either analog or digital)
- Plug-in tester (optional)
- Screwdriver (only if you need to open the outlet to fix it)
The safety precautions below are important because you will test the power outlet while it is life.
WARNING: While testing a live outlet with a multimeter, never touch the metal prong on the end of each probe. Another safety measure you can take is to hold both probes with one hand so that, in the event of a shock, the current does not pass through your body.
Testing an Outlet for Power
When testing whether power reaches an outlet, we must insert the probes into the slots after setting the multimeter to measure AC voltage.
Follow these steps:
Step 1: Set the Multimeter
Firstly, set the multimeter to measure AC voltage.
This 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 a hot connection, and the length is a 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 mentioned, 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 with caution.
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 equal to or close to the voltage rating of your mains supply (usually 110-120 volts in a single-phase US home).
If the dial does not move at all, it hardly moves a little, or the number is very low (0-2 volts), there is no power in the outlet. 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 and confirm again after removing the faceplate that there is no power. You can test by touching the probes directly to the wires and terminals inside.
Testing if an Outlet is Properly Grounded
This test is to check whether a power outlet is properly grounded.
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. The outlet is not properly grounded if it doesn’t remain the same.
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. In this case, you must open the outlet (after turning the power off) and ensure it is properly grounded.
Checking if the Wiring is Proper or Reversed
This test checks whether the wiring inside the outlet is grounded properly or reversed.
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).
If this reverse arrangement gives you a reading, the wiring is reversed.
However, this is not something you need to worry about. That’s why I mentioned above you can test for power in this reversed way, too. 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.
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