What device is used to check for live wires?

Switches

Whether you’re searching for an electrical problem or just replacing a switch, it’s a good idea to know how to test the wiring in your light switches as well. The procedure for testing a live electrical wire in a switch requires a few steps, but is ultimately fairly simple. After turning off the power, remove the plastic cover on the switch by unscrewing it. Once the cover is off, remove the switch itself by unscrewing screws from the metal mounting brackets on either side and disconnect the switch from its electrical wires by removing the corresponding screws. 

You should now have three wires, much as you would if testing exposed wiring. And as with exposed wiring, the procedure for testing the electrical wires is the same. Get your multimeter and place one test lead on the ground (a piece of metal) and the other on the wire you are testing. You can use the standardized color schemes to determine which wire is which, and the multimeter will show you if each wire is working as it should (two with zero or near zero reading, one with 110V reading). 

Safety Tips 

Safety is always a paramount consideration when working on electrics, regardless of what precisely you are doing and how simple the procedure may seem. With that in mind, here are a few safety tips to take note of so that the live electrical wiring test goes smoothly. 

Emergency Electricians

At the end of the day, the internet is a truly bountiful source for any homeowner or handyperson who finds themselves in a jam. If you don’t feel safe or comfortable working on some electricity wiring, or you’re unsure of what to do, remember there are always people you can get in touch with. Certified pros can either offer you advice or complete a thorough electrical inspection of your home for you. 

Choosing the Best Electrical Tester

Voltage testers and receptacle analyzers detect the presence of electrical voltage in cable, wires, circuit breakers, light fixtures, outlets and switches. Testers and analyzers indicate if the power is off at an outlet. They also let you know whether a device is connected properly.

• A non-contact voltage tester works well for all types of electrical work. They provide a reading without the need to touch the wires. Non-contact voltage testers emit a sound or illuminate when voltage is detected. However, they do not provide a numerical reading of any current voltage.
• Electronic voltage testers measure alternating current (AC) and direct current (DC) and give a numerical reading of the voltage present. Some electronic voltage testers also measure continuity.
• Receptacle analyzers plug into an outlet to determine whether that outlet is working properly. Some analyzers test both GFCI (ground fault circuit interrupter) outlets and standard outlets. Different lights illuminate to signal if the outlet is accurately grounded and wired. The analyzer also identifies common wiring faults if the outlet is not wired correctly.
• Circuit breaker finders identify the circuit breaker controlling an outlet. They consist of two parts: a transmitter and a receiver. The transmitter plugs into the outlet and the receiver passes over the circuit breakers in the breaker panel. When the receiver passes over the correct breaker, it emits a sound or lights up to signal which circuit breaker to turn off before working on an outlet. Some circuit breaker finders include a light socket adapter for finding the circuit breaker that controls a light fixture.
• Continuity testers determine if a light switch is malfunctioning. They measure whether an electrical circuit is open or closed. A light switch circuit is closed when the light is on. It is open when the light is off. Closed circuits have continuity and conduct electricity while open circuits do not have continuity because they cannot conduct electricity.
• Plug In Testers have LCD displays for voltage and circuit information, especially more modern ones.

It's also a good idea to check the voltage range that the device is designed to test for. The higher the voltage range, the more versatile the tool. 

Safety Tip: Be sure to turn off power to a circuit before performing a continuity test.