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An application with frequent starts and stops calls for a machine rated on

  • A.the thermal duty of the whole cycle
  • B.the peak torque of a single start alone
  • C.the steady running load between the stops
  • D.the reactive power exchanged with the supply

Answer: A

Correct answer: the thermal duty of the whole cycle

Each start draws heavy current, and with frequent starts the machine never cools between them. The rating must therefore be based on the equivalent current over the whole cycle, starts and running and rest together, rather than on any one part of it. A machine sized on the running load alone will overheat.

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