Liebert 100-1000A Circuit Breakers, SCRs, Logic Modules, Audible Alarm, 6 RS-232 Port

Theory of Operation

9.2.2Circuit Breakers

Three circuit breakers provide total isolation of the solid-state switching devices with an input breaker for each source and a load isolation breaker. Two breakers provide for maintenance bypassing of the solid-state switching devices to either input source.

All switches in the Liebert STS2 are plug-in types, which allows any switch to be replaced without de- energizing the output bus. The breakers have an interlock in the plug-in base, which prevents the switch from being withdrawn in the CLOSED position. The switch trips OPEN before it disconnects from the plug-in base.

See 15.2.5 - Circuit Breakers for specifications and more information pertaining to the circuit breakers. See Figure 14 to Figure 19 for circuit breaker locations. The circuit breaker schedule is provided in Figure 20.

9.2.3SCRs

Brick-type SCRs are used rated to carry the full 100% rated load. Because the unit is a fuseless design with non-automatic circuit breakers, overcurrent protection is provided by upstream circuit breakers.

9.2.4Logic Modules

The logic contains three separate redundant logic modules. The modules contain the logic necessary to run the Liebert STS2 and control transfers and shunt trips under all circumstances, without any outside assistance once set-up and started properly.

9.2.5Audible Alarm

An audible alarm is installed on the control board. This alarm is triggered by an alarm condition detected on the unit. The alarm can be turned off from the touch screen (Color Graphical Display units) or by a push button (LED Display units). Turning off the audible alarm does not clear or reset the condition that triggered the alarm.

9.2.6RS-232 Port

An RS-232 serial port is provided to allow an external terminal to be connected as another user interface. See 12.1 - Using the RS-232 Port on page 76 for more information on using the RS-232 port.

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