A previously used NEMA designation indicating frame size and
dimension (prior to 1965 the standard frame sizes per horsepower rating)
U.L. (UNDERWRITER’S LABORATORY)
An independent testing organization, which examines and tests
devices, systems and materials with particular reference to life, fire and casualty
hazards. It develops standards for motors
and controls used in hazardous locations through cooperation with manufacturers.
U.L. has standards and tests for explosion-proof and dust ignition-proof
motors, which must be met and passed before application of the U.L. label.