Ambient Temperature Influence

To ensure optimum matching of circuit breaker performance to the system requirements, E-T-A thermal and thermal-magnetic circuit breakers are not normally compensated for fluctuations in ambient temperature. The circuit breaker is usually subjected to the same heat source as the system so will automatically track its protective requirements.

However, some applications require the circuit breaker to operate continuously in either high or low temperatures. The following table shows the correction factors that typically should be applied. The performance of magnetic circuit breakers and type 1410 is not affected significantly within this temperature range.

Ambient temperature °C   -20     -10      0       +23       +40       +50       +60

Ambient temperature °F    -4      +14     +32    +73.4   +104    +122    +140

Multiplication factor           0.76   0.84    0.92    1          1.08      1.16      1.24

(approximate values)

Example: IN = 10 A at +50 °C. By applying the factor of 1.16 the current value obtained is 11.6 A. A 12 A CBE rating is recommended.

Close mounting of CBEs

When several devices are mounted together, an air gap between each is recommended. If this is not possible, each device should carry only 80 % of its rating.

Horizontal installation is preferable.

Plug-in Mounted E-T-A Devices:

The continuous rating capability of E-T-A sockets for plug-in circuit breakers is a function of the total number of circuit breakers fitted and the individual ratings of each. Please enquire with details of your application.

ON duty

Some applications require short-time loads with high currents (e.g. remote trip coils or higher current ratings). In order to avoid overheating, the ON period must be limited (percentage referred to cycle period).


50 % ON duty / 60 minutes:
allows a load duration of 30 minutes,
followed by a period of 30 minutes without load.or25 % ON duty / 20 minutes:
allows a load duration of 5 minutes,
followed by 15 minutes without load.