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PROPRIETARY AND CONFIDENTIAL DRAFT 28/Feb/03

Medical Gas Alarm Network System Interaction
Chapter 3: Theory of Operation

Master Alarm Wiring Conventions

The following section provides an overview of typical wiring conventions for
Master Alarm inputs and outputs (see figure 3-2 on page 3-9):

• To have the most reliable switch signalling, Hill-Rom recommends using
input switches and relays having contacts that match the following Master
Alarm electrical characteristics:

• Low voltage (approximately 20V AC)
• Low current (approximately 10 mA)

• Dry circuit applications

NOTE:
Refer to the wiring instructions from the manufacturer for specific switches
and relays.

• To comply with the NFPA 99 standard, every switch and relay must have
separate wiring to each Master Alarm.
• Polarity is determined by the indicators on the Master Alarm Breakout P.C.
Boards. Switches and contacts on signalling devices are not usually marked
with polarity indicators.
• When Master Alarms share input signals from the same pair of contacts on
switches or relays, polarity between each Master Alarm must be
maintained.
• Low pressure sensing switches are typically wired from the normally open
and common contacts to each Master Alarm.

• Maintain polarity by wiring the normally open contact wire to the
positive (+) terminal and the common contact wire to the negative (-)
terminal.

NOTE:
Normally open and normally closed refer to the state of the switch or relay in
its “shelf position” (the position of the switch or relay before the system is
operational).
• High pressure sensing switches are typically wired from the normally
closed and common contacts to each Master Alarm.
• Maintain polarity by wiring the normally closed contact wire to the
positive (+) terminal and the common contact wire to the negative (-)
terminal.
• Switches sensing both high pressure and low pressure have independently
operating sets of contacts, one set for low pressure and one for high
pressure.

Page 3 - 8 MedPlus TotalAlert™ Alarm Network Operation and Maintenance Manual (man291ra)