Different sizes of electrical cable can carry different amounts of current. Cable is measured in American Wire Gauge (AWG). A larger AWG number indicates a smaller cable. Attempting to run too much current through too small of a cable can cause permanent damage to wiring. It can also start an electrical fire. Fortunately, there are a number of ways to identify the size of an electrical cable. These methods only require minimal equipment and are effective for virtually all cables.
Look at the insulation on the cable. Search for text written on the insulation. The last numbers in each string of text represent the AWG of the wire. If you cannot find any text on the wire, proceed to the next step.
Cut the wire with your wire cutters. The cut should be perpendicular to the run of the wire.
Measure the diameter of the cross-section in inches. The diameter is the distance from one side of the cross-section to the opposite side in a straight-line. Do not include the wire's insulation in the measurement.
Divide the diameter of the wire by .46. Take the logarithm of this result by pressing the "log" button on your calculator while the result of the division is on the screen. Divide the logarithm by -.050305. Subtract three from the final value. This gives you the AWG of your wire.
Turn the Windows calculator (accessible from the Start menu) into a scientific calculator by selecting "Scientific" from the "View" menu at the top of the window.