U
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"U" FRAME
A previously used NEMA designation indicating frame size and dimension
(prior to 1965 the standard frame sizes per horsepower rating).
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 motor and control for 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.