How to Identify Electrical Wire Gauge

A close shot of two pieces of electrical wire connected to a battery.
What You'll Need
Voltage tester
1/4 " blade or #1 Robertson Screwdriver
Wire strippers
Electrician's pocket reference manual

Knowing the gauge of electrical wire is essential to an electrician. This is what tells an electrician how many amps any one wire can actually carry without heating up. If the current you are trying to pass through a specific wire is more than what's rated for this particular wire gauge, the current going through will be generating heat throughout the line causing deterioration of the wire and its insulation and over time, the risk of an electrical fire.

Your home requires much more electricity than your individual appliances; this is the reason why a cable running from a utility pole is much larger than the in-wall wiring of the house. This article will show you how to identify the electrical wire gauge yourself.

Step 1 - Expose the Wire

NEVER WORK AT ANY ELECTRICAL WIRES, JUNCTION BOXES, PLUGS OR SWITCHES WITHOUT FIRST SHUTTING THE POWER OFF AT THE CIRCUIT BREAKER! Before you expose the wires in any circuit box or outlet, always make sure that the power is turned off by trying to turn on the light, checking the plug with a plug-in appliance, or by using a voltage tester. Never touch the bare wire with your bare hands; long nose pliers have insulated handles to serve that very purpose so always make this a regular practice.

You will first remove the faceplate or the cover from the electrical box to get to the wires themselves. Inside, you will see several wires attached to a switch, a light socket, a plug, or you'll often even see several wires attached together with an electrical connector. Use the proper screwdriver to loosen them or unscrew the connector to take the wires apart.

Step 2 - Determine the Size of the Wire

In recent years, the color of the cable has been used to indicate the AWG size of the wires inside it, while the wire's insulation itself indicates the polarity of the wire either if it's neutral or hot. You can use a common wire stripper, however, to determine the diameter or the gauge size of the wires. Most wire strippers have a series of round holes labeled with AWG sizes where you can insert the wires. You not only can strip wires of a specific size but can also determine the gauge size of the wire.

First, determine the proper hole to insert the end of the wire through. You want the wire to be able to move into it with ease without using a hole that is too large. If the wire goes through a hole with force, the hole you are using is too small. Once you find the right one, the number stamped by the hole on the wire stripper indicates the gauge size of the wire. If all you know however is the diameter of the wire, you can consult a reference manual, online or hardcopy, listing all electrical wires by AWG size and also by their use.