Before working on any electrical system, you need to determine if it is powered and if any of the end-points or waypoints have power, too. In some cases, you may need to calculate voltage levels.
The good news is that this is easy for most homeowners to do on their own. In fact, testing an electric outlet can be as simple or as complicated as you like. Methods range from easy and free (by using a working lamp) to an extremely expensive device that uses radar waves.
Shutting off a circuit breaker is no guarantee that you will not receive a shock. Circuit breakers are frequently mislabelled. Or two circuits may be wired together to feed one device. Shutting off the large breaker panel main switch will safely shut off any circuit that you are uncertain about. But it's important to remember that this shuts off all of the power in the house.
If you have any reservations about working with household current, call an electrician. While electrical work is one of the more expensive trades to call to your house, determining whether power is running to an area of the home or calculating its voltage is a routine and generally brief task for most qualified electricians.
How to Test an Outlet by Plugging in a Working Light
This classic method of testing for power could not be simpler. If the current is running to an outlet, then it will power a light. If there is no power, there is no light. That is the simple premise behind this method. To test any outlet from the electric service panel:
- Depending on the size of your house, start with a 50- foot or 100-foot extension cord and plug a work light into the end of it.
- Plug the extension cord into a working outlet so that the light turns on.
- Unspool the cord, running it through the house, all the way to the electric service panel.
- Hook the light on a nail near the panel.
- Progressively turn breakers off and on until the light turns off. That will be the breaker controlling the outlet. Label the breaker accordingly.
This method works well for mapping circuit breakers around the house. It can tell you when an outlet's circuit is on or off. It's ideal for a house that you've just moved into that has unmapped or poorly mapped breakers.
How to Test an Outlet or Wire With a Voltage Tester
Cheap and easy to use, a small hand-held voltage tester represents the sweet spot in electrical testing tools for do-it-yourselfers.
A voltage tester, often called a non-contact voltage tester, can detect electrical current without touching the exposed wires.
- Insert batteries into the voltage tester. Make sure that the batteries are fresh and that they are facing in the right direction.
- Turn the voltage tester on.
- Test the voltage tester on a working outlet by inserting the tip into the "hot" side of the outlet.
- Return to the device or wire that you want to test.
- Hover the tip of the voltage tester about 1-inch from the wire and the tester will chirp and flash if a current is detected.
A voltage tester is simply an on-or-off tool. It cannot test variations in power. It only will tell you if the power is on or off.
One downside of these pen-style voltage testers is that they cannot detect current in low voltage devices, such as pathway lights or small home appliances. For lower voltages, you need a multimeter.
How to Test a Voltage Tester
If the batteries on a voltage tester fail, the current may appear to be dead even if it is live. You should always test the voltage tester on a known live circuit before using it.
Even if the batteries are good, these items are notorious for providing false-positives and false-negatives. A false-positive is when the tester beeps, but there is no current. Of greater concern is the false-negative, when the device does not beep even though the current is flowing.
- Find an electrical receptacle that you absolutely know is live. Typically, this is a receptacle that is already verifiably powering a large appliance, radio, TV, computer, or small kitchen appliance like a blender.
- Make sure that the outlet is powering the device by turning the device on. Be sure to check both the top and bottom portions of the outlet.
- Insert the end of the voltage tester in both straight slots of the live receptacle. Depending on your model, the tester should flash, beep, or both flash and beep if the current is live. If the outlet is wired correctly, the test will indicate voltage only when inserted in the short "hot" slot but not the long neutral slot or the rounded ground slot.
For the safest operation, insert the end of the voltage tester into both slots of the receptacle. A flashing light or beep indicates if the current is live.
As an additional precaution, after you open up the receptacle to work on it, you should once again test each wire inside of the box. A voltage tester is usually designed to be non-conductive so that even if it came into contact with a live wire, the power should not transmit through the device.
How to Use Voltage Tester to Test Electrical Cords
A voltage tester can also be used to determine if an electric cable, extension cord, or light cord has power.
Hold the tip of the voltage tester against the side of the electrical cord. Be certain to touch around the cord. Three major wires (positive, neutral, and ground) run through most electrical cords. The voltage tester indicates a live current only when it is against the positive, or hot, wire.
Test Wiring With a Multimeter or UWB Device
While they are highly accurate, multimeters are more elaborate and provide more information that most DIYers need for home electrical use. Also, multimeters can be difficult and confusing to use for many do-it-yourselfers and thus may lead to injury.
However, for lower voltages and for determining what that voltage is, you will need a multimeter.
Multimeters have been used and adopted by millions of amateurs throughout the years. The note of caution is to become fully educated in the operation of multimeters before attempting to use one.
Ultra-wideband (UWB) radar devices are not used for normal detection of live currents. However, a UWB device is the only tool available on the consumer market that will detect powered-up, live electrical cables behind drywall, without tearing out the drywall.
Because of its extremely high cost and difficulty of operation, a UWB device is not a practical tool for do-it-yourselfers who wish to detect the presence of voltage.