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Forums > Engineering Questions and Answers > Electrical Engineering
why device are used having more current rating than the required current
Last Post 25 Jul 2013 09:07 AM by Mike McGregor. 1 Replies.
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priyadarshictc
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Posts:1

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26 Mar 2013 02:01 AM
    As i am doing a trainee engineer in control pannel industry i saw for a 1 kw motor and 0.5 watt heater there are mpc of 25A contactor of 18A
    smps of 10A and motor of 1kw 9A in the pannel and the supply is single phase. SO why this much current ratings are used as it only requires 4a cureent.
    Mike McGregor
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    25 Jul 2013 09:07 AM
    The contactor and smps are overspecified in order to accommodate the initial surge current of the motor at start-up. The circuit breaker, however is incorrect. It should have a lower tripping current than the components it is designed to protect. It is normal practice to install a type-C circuit breaker in order to accommodate the motor initial surge, rather than choosing a breaker with a higher trip level. The motor-contactor should also have a thermal overload fitted.
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