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Insulation monitors secure power supply

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05.03.2008

For early detection and correction of insulation faults, the Siemens Building Technologies Division now offers two new rack-mounting units: the 7LQ3 354 and 7LQ3 355 insulation monitors. They monitor non-grounded power supplies in medical premises, detect insulation faults as soon as they occur, and output warning signals.

Mains-dependent medical equipment must remain in operation even when threatened with a short-circuit to frame, or when the general power supply fails. The 7LQ3 354 and 7LQ3 355 insulation monitors guarantee this by monitoring the insulation resistance of the non-grounded power supply as well as the load current and the temperature of a transformer. On the 7LQ3 354, the alarm value of the insulation resistance is 50 kilo-ohms (fixed).

The 7LQ3 355 monitor also offers an adjustable response threshold of 50 to 500 kilo-ohms. In addition, a line of color LEDs indicates the current insulation status between 20 kilo-ohms and 1 mega-ohm. Users can thus see the plant status at a glance. Changeover contacts can be used to connect the devices to the building automation system or to the relevant medical monitoring system. The insulation monitors can even be installed in existing systems. The 7LQ3 355 monitor is compatible with the 7XV93 test and signaling combinations from Siemens.

If the voltage drops below 90 percent of the rated value, the 5TT3411 and 5TT3412 voltage relays transmit the signal for switching to a second mains supply to secure the continued operation of the medical equipment. This means they are suitable for the secure power supply not only of medical premises but also of other sensitive areas such as server systems, etc. The new voltage relays are suitable for single-phase (5TT3411) and three-phase (5TT3412) supply systems.

Volker M. Banholzer | Source: Siemens A&D
Further information: www.siemens.com/beta

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