How to Test if an Electrical Cable is Live
Working with electrical cable is not a job you should take lightly. As you begin any electrical project, you may find yourself at risk for electric shock, but this risk can be compounded upon by confusing or disorganized wiring if someone else did a poor job previously. You should therefore almost always turn off the power to an area before you begin such work to minimize the risk to your safety. One of the only exceptions is if you need to know which wire is live or hot before turning it off. This article will show you how to safely determine which electrical cable is live.
Step 1 - Know the Standards
Home wiring has to be up to code, which means that the wires you find inside an electrical box will be appropriately color-coded. However, this does not mean that someone did not come along and change things around in a repair attempt and, in the process, use a different color of wire. Thus, it is smart to know the standards but also smart to not take their word for it.
In standard residential wiring, the black wire is the live wire, and it is what you should find attached to the spade or brass terminal. A green wire is typically the ground which provides another path for the electricity to travel. It is there to save your life in the case of a surge or short, so always make sure it is attached correctly during an electrical job. Sometimes the ground wire is also yellow or has a yellow stripe.
The neutral wire should be white. Circuits are only made when there is a complete path for the current to flow, so this neutral is a necessity. It should be connected to the wider space or the silver terminal.
Some outlets will also have what is known as a traveler wire that is red. This can connect a three-way switch.
Step 2 - Gain Access to the Electrical Cable
Use the screwdriver to remove the face plate or the box cover. Make sure you do not touch any wires with the screwdriver and that you are grounded with the wrist strap. You don't need to remove wires in order to test them for current, so do not try to touch them either.
Step 3 - Test the Electrical Cable for Current
You can use either a current tester or a voltage meter to determine if an electrical cable is hot. Keep in mind that it is possible for more than one wire to be live.
Touch the tip of the meter or tester to the screw where the wires are attached. Go slowly and keep your eyes and ears open. When current is found, the light will go on and the machine will beep. As you go, be sure to test between the wires as well. If current is flowing between two wires, the voltage meter will read 0.