Protect your electrical equipment

Three-phrase service

SRP delivers "single-phase" or "three-phase" service to customers depending on their specific power requirements. The electrical needs of most homes and small businesses can usually be met with single-phase services, commonly recognized as a 120/240-volt service.

Some residential and business customers have electrical equipment requiring a three-phase service rather than a single-phase service. These customers can include large industry, shopping centers and even some homes. Air conditioners larger than 5 tons, commercial refrigeration, motors and pumps are all examples of equipment needing three-phase power to operate.


The electric service SRP provides to its customers is among the most reliable in the Southwest. However, all electric distribution systems are subject to occasional fluctuations in power quality, such as voltage sag, harmonics, voltage transients and/or spikes and flicker. These occasional fluctuations can cause damage to certain types of equipment.

All customers are ultimately responsible for protecting their valuable electrical equipment. Depending on your type of electric service and how the service is used, additional steps may be warranted to ensure that your equipment is properly protected.

Protecting your equipment

Three-phase equipment requires three energized lines to run properly. With a loss of voltage on any one line, unprotected three-phase equipment may continue to run, possibly causing overheating. This could result in equipment damage or failure.

This type of interruption is referred to as "single phasing" and may be caused by acts of nature, such as lightning, falling tree limbs, wind, automobile accidents, electrical problems within your facility, or even a cyberattack on the system.

The National Electrical Code (NEC) requires thermal protection when there is a single phasing event. Typical thermal protection, such as fuses, breakers or overload devices, may not be sufficient to protect your three-phase equipment when single phasing conditions occur. Fortunately, various protection devices are available that will give you this added protection. These devices, installed by a licensed electrician, can protect against phase loss, phase imbalance and over-voltage conditions. Phase loss monitoring devices with an automatic resetting feature may also be a key consideration to protect critical systems such as refrigeration equipment.

This type of protection is a worthwhile investment, considering the high cost of three-phase equipment and the potential inconvenience of being without this equipment should it be damaged.

Customer responsibility

Please remember that customers are responsible for properly protecting their electrical equipment because, as infrequent as they are, power interruptions do occur. So have a licensed electrical contractor inspect your three-phase equipment and install added protection if needed.

If you have any questions, please contact your Strategic Energy Manager. For troubleshooting, call (602) 236-8855.

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