wire gauge voltage loss calculator

Wiring in many cases is a slightly lower priority subject when discussing electric locks and door access control installation. Many installers and do-it-yourself people use a wire gauge that they are familiar with, usually 18 or 22 gauge. However, it is important to account for potential voltage loss over longer wire runs. At Maglocks, our advisors are always available to assist with wire selection and gauge requirements. In addition, the following formula and example provide a simple approach for figuring out the general voltage drop (or loss) in a given current.

Understanding Wire Resistance (Ohms)

To calculate voltage loss, use the Ohms table below to derive the resistance per 1,000 feet of wire. [Wire gauge resistance / 1,000 feet in Ohms @ 77 degrees Fahrenheit (25 degrees Celsius)]

Note: Ohms figures are sourced from the National Institute of Standards and Technology. NIST is a measurement standards laboratory, and a non-regulatory agency of the United States Department of Commerce.

Voltage Loss Equation Example

understanding your results

Using the example from above: If you have an electric strike that takes .3 amps at 24 volts, you will find you are left with 21.07 volts at the strike by the time you send the power out through 1,500 feet of 18 gauge wire. This is calculated as [24 volts less voltage loss of 2.93 volts = 21.07 volts or 87.8%]. This would usually fall within the tolerances of the electric strike.

However, if you are installing a 12 volt electric strike at the same current and wire length, you would only have 9.07 volts at the strike [12 volts less voltage loss of 2.93 volts = 9.07 volts or 75.6%] which would not fall within the nominal 10% to 15% variance given by most manufacturers. In this case you would only have approximately 75.6% of the rated voltage needed to power the strike. The result would be marginal, intermittent operation of the hardware.

If you increase your wire length you must increase your wire gauge. Likewise, the lower your voltage, the larger your wire gauge must be. Therefore you should calculate the voltage loss and make your wire selection based on your findings.