What does it mean when a specification calls for a 100% rated circuit breaker?
The National Electrical Code (NEC) specifies that circuit breakers may only be loaded to 80% of their marked ampacity on a continuous basis. An exception to this rule allows 100% continuous loading if the circuit breaker is marked “100%”. Siemens 2004 SPEEDFAXTM shows the part numbers and prices for breakers available with 100% ratings. These breakers may be loaded to 100% of their rating and must be used with specific lugs, as shown in Siemens literature, and are for use with 90 Deg C cable. One important aspect of the use of 90 C cable is that it must be sized based on the 75 Deg C ampacity.
