What is the de-rating factor for applying a thermal magnetic circuit breaker at ambient temperatures above the standard 40 Deg. C?
UL489 dictates that circuit breakers be calibrated at 40 Deg. C ambient. Due to the thermal element in a thermal magnetic circuit breaker, the breaker will trip at lower currents in higher ambient temperatures, causing nuisance trips. The Siemens 2004 SPEEDFAXTM, page 6-100 has a table of de-rating factors for up to 60 Deg. C for thermal magnetic circuit breakers. However, since trip characteristics of electronic trip circuit breakers are not affected by ambient temperature, Siemens recommends using electronic trip circuit breakers in these applications.
