GAI-Tronics 379-002 Monitored RElay Module (MRM) Stations - Manual (Page 7)

Pub. 42004-491A
Model 379-002 Monitored Relay Module Station Page 7 of 13
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Mode 2: IDC Single Normally-Open (N.O.) Switch
In this configuration, only one normally-open dry contact closure may be installed per supervised line. In
this mode, the loop is monitored for open circuits, wire-to-wire short circuits (across + and −), and ground
faults. When the contact closure is not active (open), the loop appears as 20.1 k
 load (15 k in series
with 5.1 k ). This appears on the input to the MIM and indicates a healthy loop. When the contact
closure is active (closed), the 15 k  resistor is bypassed.
Figure 5. IDC Single Normally-Open Switch
When the contact closure is active (closed), the 15 k  resistor is bypassed. In this case, output #1 only
sees a 5.1 k  load. When this occurs, it indicates to the MRM that the contact closure is active. If there
is a short across L1 and L2, if either leg is grounded, or if a break occurs on either leg, the MRM indicates
that a fault has occurred.
N OTE : The terminating resistors are not included with the MRM. These resistors are included in a kit
(12509-004), which must be ordered separately.