How to Determine Electric Wire Size

Electricians have used The American Wire Gauge, also known as the Brown and Sharpe Wire Gauge, in the United States since 1857 to measure the size of round, electrical wire. The American Wire Gauge is an inverted numbering system--the larger the number the smaller the wire's physical sizes. The American Wire Gauge Wheel measures the diameter of nonferrous wires from AWG #40 through AWG #0000 or 4/0 or –4. The American Wire Gauge Wheel works with solid wire; you will need to use a set of dial or digital calipers to measure the size of stranded wire.

Things You'll Need

• Wire cutters
• Wire strippers
• American Wire Gauge Wheel
• Dial or digital calipers

Instructions

Using the American Wire Gauge Wheel

1. Cut the wire flush with the insulation and strip off ½ inch of insulation. You want to start with a freshly stripped section of wire to get the most accurate reading with the American Wire Gauge Wheel. Flat spots on the wire will lead to an erroneous gauge reading. Set your wire stripper's depth of cut using a scrap piece of wire so that it just cuts through the insulation without biting into the wire itself. This is crucial because copper and aluminum are soft metals and it is possible to scrape enough off to lead to an improper sizing of the wire.

2. Insert the stripped end through a hole in the wire gauge and try pulling the slot associated with that hole over the wire. When you have found the right hole and slot combination, the slot will move over the bare wire with just the smallest amount of drag.

3. Repeat the above step using one hole above and below the one you feel is the correct hole in the wheel to double-check. The wire will pass through the larger hole with no apparent drag and will not pass through the smaller slot at all if your original selection is correct.

How To Measure Stranded Wire

1. Strip a 1/2 inch of wire. The proper adjustment of the wire stripper depth of cut is especially critical when working with stranded electrical wire because you can cut though the strands. The problem with that is that if you are working with wire composed of many thin strands you might not notice one or two of them dropping off the wire.

2. Practice using the dial calipers with scrap wire before attempting to make an actual measurement that is crucial. You need to develop a light touch because the caliper's jaws can distort the stranded wire and produce a false reading if you close them too hard against the wire.

3. Take the actual reading and compare the decimal reading to the decimal sizes in the wire table to get the wire gauge.

References

• "National Electrical Code"; National Fire Protection Association; 2008 Revision
• University of Illinois Urbana-Champain: American Wire Gauge (AWG) & Metric Wire Gauge Wire Sizes
• Interfacebus: Reference & Information AWG Cable Description

Resources

• RBEElectronics: Wire Gauge Tables