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Why can't I select the ampacity of the primary main circuit breaker in my Isolated Power System?

Issue:
Product Feature
Product Line:
Hospital Isolated Power Systems
Environment:
NFPA 99, NEC 517.160
Cause:
The ampere rating of the primary main circuit breaker may not be changed.
Resolution:
Medical panels are tested and UL Listed as a complete piece of equipment and the primary main breaker size is specified by UL; therefore, the customer does not have the option of specifying the breaker size. UL1047 Art. 23.1 Overcurrent protection provided for the primary circuit shall be rated not more than 125% of the ampere rating of the primary circuit.  Exception: The next higher standard rating is acceptable if 125% of the ampere rating does not correspond to a standard rating of a fuse or circuit breaker. For a transformer rated less than 1000 VA, the overcurrent protection shall not be rated more than 167% of the primary current.Conclusion: The panel cannot bear a UL mark if furnished with a main circuit breaker rating exceeding the value specified by UL.
 
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