Compact® NSF and NSJ 150 to 600 A Circuit Breakers
Section
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:
| 45° C | 50° C | 55° C | 60° C | 65° C | 70° C |
| 0.975 | 0.95 | 0.925 | 0.90 | 0.875 | 0.85 |
Example |
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What is the tripping time for a TM200DP circuit breaker with a 400A fault current and an ambient | ||||||
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•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.
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