How to Tell the Diameter of an Electrical Cable

Whether you need to fit cable into a tight space or drill holes to run cables through your house, knowing the diameter of your electrical cable is key. Common measuring instruments such as a tape measure or ruler are not accurate or convenient when measuring cylindrical objects. With the help of a vernier caliper, which is an instrument used to measure two opposing sides of an object, you can measure the diameter of your electrical cable with accuracy.

• 1

  Turn off the electrical cable you measure. Unplug the device from its wall electrical outlet. Handling electrical cable attached to electricity can unplug the device or rupture the cord and create sparks or electrical shock. So measure only electrical cable that is not flowing with electricity.

• 2

  Open the vernier caliper by twisting the knob or sliding the slide bar. The caliper should be open just a little wider than the diameter of the electrical cable.

• 3

  Place the electrical cable between the two clamps of the caliper on the centimeter reading side.

• 4

  Turn the knob or slide the slider of the vernier caliper slowly until the electrical cable fits snugly between the two opposing clamps. Do not turn the knob or push the slider so the clamps dig into the cable because you could cut the cable.

• 5

  Write down the number the caliper reads in millimeters. To calculate the number of whole millimeters, locate the "0" mark on the sliding bar. This bar indicates millimeters. The whole number of millimeters is read by using the number to the left of the "0" millimeter tick mark on the fixed centimeter scale. For example, if the centimeter scale reads "2" and the "0" millimeter tick mark is between the 2.1 and 2.2cm marks on the centimeter scale, then the total number of whole millimeters is 21.

• 6

  Write down how many tenths of millimeters the caliper reads. Locate where the tick mark of the millimeter sliding scale lines up with the tick mark of the fixed centimeter scale. Then count how many centimeter tick marks appear away from the "0" on the millimeter slider. For example, for seven tick marks, the total would be 0.7mm. If that were added to the example's 21 whole millimeters, then the diameter of the electrical cable would be 21.7mm.