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What is the meaning of the items screen-printed on the setting selector switches of the Micrologic and STR electronic control units.

Standard IEC 60947-2 defines the names of the selector switches.

The meanings of the screen-printed items on the selector switches of the trip units are:
 
Ir:  adjustment of the long time (or thermal) setting. This is a multiplication coefficient of the rating of the device. Role: protection against overloads.

tr:  long time delay in seconds, enabling in particular the starting current of a motor to be tolerated.
 
Isd:  short time ("magnetic" or "Im"). This is a multiplier of the Ir setting, often 1.5 to 10 times the Ir current. Role: protection against short circuits.

tsd:  short time delay, enabling in particular the discrimination (time) to be increased with downstream feeders and the magnetisation peaks of a transformer or a motor to be tolerated. It is recommended that the I²t selector switch is set to the ON position.

Ii:  instantaneous current. Role: protecting the installation against strong short circuits (dead short circuits) by instantaneous tripping and self-protection of the circuit breaker. The li setting must be higher than the Isd setting.

Ig:  I earth or earth protection. Role: for monitoring the earth fault current circulating in the PE conductor in TNS systems.

tg:  earth protection time delay. 

I delta n:  adjustment of the sensitivity of the earth leakage protection (Micrologic 7.0 or Vigi module)

delta t:  earth leakage protection delay.
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