9065CT9701R03/21

Calculating the Trip Current for Ambient Temperatures Other than 40 °C

Ambient Temperature Correction Curve for Thermal Overload Relays

A controller ambient temperature other than 40 °C (104 °F) trip current can be calculated by applying a correction factor from the curve in the figure Ambient Temperature Correction Curve for Thermal Overload Relays. The approximate trip current for a particular ambient temperature is the product of: (1) the multiplier M corresponding to the temperature and (2) the 40 °C trip current rating.

NOTE: Ambient temperature is the temperature surrounding the starter enclosure. Normal temperature rise inside the enclosure has been taken into account in preparing the thermal unit selection tables listed in the section Thermal Unit Selection Tables.

Example 2:

Determine the trip current for the motor and controller as shown in the Example 1 in Procedure for Calculating the Trip Current Rating, except the controller is in a 30 °C (86 °F) ambient temperature. From the curve in the figure Ambient Temperature Correction Curve for Thermal Overload Relays, the multiplier M is 1.1 at 30 °C. The approximate trip current is 16.0 × 1.25 × 1.1 = 22 A.

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