Proper Service Voltage Ranges

Normal Voltage Ranges

Maintaining the right voltages is important for the effectiveness and durability of your electrical equipment. Voltages that are too high or too low can make irrigation pumps, electric dryers, lights and other equipment less efficient.

Our Part

As part of our commitment to safety, reliability and affordability, Idaho Power follows the American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60Hz) (ANSI C84.1). This standard describes the normal ranges for voltage delivered to your point of service (the electric meter), and end-user equipment voltage ratings.

Based on this standard, we strive to keep voltages delivered to your point of service within 5% of the nominal voltage (120V, 208V, 240V, 277V and 480V) under normal operating conditions. So if the nominal voltage at your meter is 480V, we strive to keep the voltage delivered to it between 456V and 504V.

What You Can Do

A separate standard, The National Electric Code, recommends limiting the additional voltage drop — beyond the 5% fluctuation — between the meter and the outlet or equipment in your electrical system to 5% or less. Equipment that meets the ANSI C84.1 voltage standard should perform adequately even with this additional voltage drop.

For example, if a service point with a nominal voltage rating of 480V operates at 456V, and voltage drops an additional 5% — 24V — the voltage at the end-user equipment will be 432V. That’s still within the normal voltage range.

Major voltage deviations are rare but could occur during abnormal conditions like a transmission line outage, or due to other factors beyond Idaho Power’s control. Voltage relays can help protect equipment like motors from over-voltage, under-voltage and voltage unbalance. An electrician can help you select voltage relays or other protective devices for your electrical system.


Contact Idaho Power’s Customer Service team at 208-388-2323 or 1-800-488-6151.