Specifications

49
COMPACT
®
NS circuit breaker
Effect of high temperatures
COMPACT
®
NS circuit breaker: supplementary technical information
Trip curves
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°C50°C55°C60°C65°C70°C
0.975 0.95 0.925 0.90 0.875 0.85
Example
For a TM200DP circuit breaker, a 400 A fault current and an ambient temperature of
40°C. What is the tripping time?
■ 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.