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Compact® NSF and NSJ 150 to 600 A Circuit Breakers
Section 13—Supplementary Technical Information
© 1995–2003 Schneider Electric All Rights Reserved
60
EFFECT OF HIGH TEMPERATURES
When the ambient temperature is greater than 40° C, overload protection characteristics are slightly
modified. When determining tripping times using time/current curves, the Ir values corresponding to the
thermal setting on the circuit breaker must be reduced using the coefficients below:
Example What is the tripping time for a TM200DP circuit breaker with a 400A fault current and an ambient
temperature of 40° C?
• Ir = 200 A
• I/Ir = 400/200 = 2
On the time/current curve, t = 100 s.
Consider the same conditions, except an ambient temperature of 65° C. What is the tripping time?
• Ir = 200 x 0.875 = 175 A
• I/Ir = 400/175 = 2.28
On the time/current curve,
≈ 65 s.
45° C 50° C 55° C 60° C 65° C 70° C
0.975 0.95 0.925 0.90 0.875 0.85