APC MX28B-2400 User Manual

MX28B-1200   PRODUCT MANUAL 

Revision B 

24 MX28B-1200/2400 

 

Four external alarm inputs with assignable priority levels are available.  These alarm inputs 
respond to external dry contact closures between normally open (NO) and common (C) or 
contact openings between normally closed (NC) and C (see Table 5-1). 

Table 5-2 shows the external alarm input connection designations.  Connector J4 is located on 
the alarm interface board mounted in the space above the control unit.  Systems are shipped with 
jumper wires connecting each NC and corresponding C contact.  A jumper wire should be 
removed only if the corresponding NC-C contacts are going to be used. 

 

#1 
#2 
#3 
#4 

NO1-NC1-C1 
NO2-NC2-C2 
NO3-NC3-C3 
NO4-NC4-C4 

___________________________ 
___________________________ 
___________________________ 
___________________________ 

There are eight alarms available that provide outputs via Form “C” relay contacts.  The last two 
of these are pre-assigned as the Minor and Major alarm outputs.  The Major relay is energized 
(NO-C contacts closed) during normal (non-alarm) operating conditions; all the other relays 
energize when an alarm condition occurs.  The other six outputs are initially designated as 
“Relay 1” through “Relay 6” (the user may assign more meaningful names if desired).  The 
various system alarm conditions can be assigned to any of the eight alarm outputs. 

Table 5-3 shows the alarm output connection designations.  Connectors J1 and J2 are located on 
the alarm interface board mounted in the space above the control unit.  The relay contacts should 
only be used to switch resistive loads of 0.5 amperes or less at 60 volts or less. 

 

OPEN 

CLOSED 

NO-C 
NC-C