Design Considerations in Medium Voltage Starters for Underwriters´ Laboratories´ Standards

The main design and test requirements for motor controllers in the 2200 V to 5000 V range as given in Underwriters´ Laboratories Standard UL 347 are outlined. The ways in which these requirements are met in a typical starter are described. Design requirements are reviewed on guarding live parts, grounding, wiring space, isolating means, and interlocking. The extensive performance test program specified in the standard is described, including operating tests, short- time capability tests, temperature tests, dielectric tests, overload tests, and short-circuit interruption tests.