Nortel Networks OPTera Metro 3500 - Manual (Page 271)

Hardware feature descriptions 3-43
Planning and Ordering Guide—Part 1 of 2 NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
Power Input Alarm
This circuit detects input power failure. A green light “on” indicates normal
operation. If input power has been lost, this light is off. In normal operation,
the power input alarm external relay contacts are in an energized or powered
state. The contacts are in a deenergizing or powered-off state when input power
is lost, providing C to NC closure for the alarm state.
Breaker Alarm
Breaker alarms operate in one of two ways. Both methods have a red indicator
light “off” for normal operation and “on” when the alarm circuit is activated.
The first method uses indicating type breakers that provide a mechanical
connection to activate the alarm card. The second method uses open-circuit
electronic sensing across the fuse holder. Open-circuit detection usually
requires a reset switch to clear the breaker alarm.
Both methods have the breaker alarm external relay contacts deenergized or in
a powered-off state for normal operation and energized or in a powered-on
state when a breaker alarm is detected, providing C to NO closure for the alarm
state.
Bay Alarms
Bay alarms are visual indications for the rack frame (system level). These
alarms can be a combination of three different levels: critical, major, and
minor. Critical alarms are red; a major alarm can either be a red or yellow; and
the minor alarm is always yellow. The external alarm contacts are deenergized
or in a powered-off state for normal operation and energizing or going to a
power-on state when an external alarm is detected. Activation of these types of
alarms comes from external equipment alarm contacts that are either in the
rack frame or system and provide an alarm ground to the input ports of the
alarm system.
Alarm Circuits
Most monitoring alarm systems require an alarm ground signal to activate the
individual alarms.
The most common, is a single-point contact or paralleled contact
configuration. An alarm ground wire connects to the common of the external
relay contact, and the associated NC or NO contact connects to the alarm
monitoring system. When the alarm activates, the relay closure between the C
and either the NC or NO sends an alarm ground to the alarm monitoring
system, activating the appropriate alarm. Multiple relay contacts can be
paralleled in this configuration to activate a single or multiple input to the
alarm monitoring system.