North American certification

The following is a brief summary of the different categories of ordinary-use location motors and the Standards used to investigate them. The category classification designations are provided to facilitate easy identification of companies that have products under these categories online.

UL's Recognition services and Listing services

Two of the most common UL services are Listing and Recognition. A Listed device is considered complete and can be used on its own, whereas a Recognized device is normally a component of another product. It is usually incomplete in some manner so that the suitability of its use cannot be fully determined until it is investigated in the end use.

A Recognized device has a list of conditions-of-acceptability that identifies concerns that need to be considered in the end use. Even though an additional investigation of a Recognized Component is needed in each end use, by using Recognized Components, a significant amount of time and cost can be saved.

Electric motors

UL 1004-1

An electric motor takes electrical energy and converts it to mechanical energy.

Listed motors (category PRGY) are intended to be installed in the field rather than at a factory as a component of another product. UL evaluates Listed motors to determine compliance with the construction and performance requirements of UL 1004-1, the Standard for Safety of Rotating Electrical Machines -- general requirements. Learn more about our motor listing service.

The motor is also tested to determine whether it can operate at its rating without creating a safety hazard. This testing includes an input test which shows the motor can carry rated current at the rated load (horsepower or watts), and a temperature test to show that the motor components do not exceed their rated temperature limits.

While the motor sample is still in a heated condition, a dielectric voltage-withstand test is performed to evaluate the insulation of the motor. Listed motors also undergo testing to evaluate the integrity of the motor enclosure. Recognized motors (category PRGY2) are intended to be used as a component of another product and installed in the end-product factory. The Recognized motors in this category are also evaluated to verify that they will safely perform in accordance with marked ratings. However, there may also be tests performed on parts of the motor to certify that components are suitable for the intended use such as plastics used as part of the insulation system or non-metallic functional parts. These tests apply to both Recognized and Listed Motors. Most end-product categories require motors to comply with these basic requirements.

Component motors protected from overheating

UL 1004-2 and UL 1004-3

Thermal protection for motors is required on most end-use products. There are several categories that cover these types of motors -- two major ones are impedance and thermal protection.

Impedance protection is when the windings of the motors are designed to limit the amount of heat generated in abnormal situations such as a locked-rotor condition. Impedance protected motors are normally small motors such as the shaded pole type. Impedance protected motors are in category XEIT2.

Impedance protected motors are subjected to an 18-day locked-rotor test. During the first three days, temperatures are monitored to determine if the motor is operating within its limits. At the end of the test, a dielectric voltage-withstand test is performed to determine if the motor insulation is still effective.

Thermally protected motors have a protective device electrically in line with the power source. The protective device opens the circuit if the motor windings become too hot. Protective devices include automatic resetting type, manual resetting type, self-holding type, thermal cutout type, and single-operation type. Thermally protected motors come in all shapes and sizes. They are found in category XEWR2.

For thermally protected motors, specific tests need to be considered. For instance, a running overload test is often performed to evaluate a common failure mode. If the motor will only be used as a fan, a fan duty test is needed. The locked-rotor heating and endurance tests are almost always required.

Fire pump motors

UL 1004-5

UL also provides Listing of fire pump motors. UL worked with representatives from the fire pump companies, motor manufacturers, fire pump controller manufacturers, installers, NFPA and NEMA to develop requirements that meet the needs of all involved parties. Fire pump motors are found in the category QXZF.

Fire pump motors are used in conjunction with a fire pump in sprinkler systems.

The fire pump motor is subjected to a battery of tests to check that the motor is suitable for this use. These include the temperature, locked-rotor, duty cycle, and dielectric voltage-withstand tests.