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The Isolator Module
2.7
The Isolator Module
The Loop Isolator Module (I300) is used to protect critical elements of the com-
munications loop from faults on other branches or sections of the loop. The I300
continuously monitors the circuit connected to Terminals 1(-), 3(-), 2(+) and 4(+).
Upon power-up, an integral relay is latched on. The I300 periodically pulses the
coil of this relay. A short circuit on either side of the loop resets the relay. The
I300 senses the short and disconnects the faulty branch by opening the positive
side of the loop (Terminal 2 or 4). This effectively isolates the shorted branch
from the remainder of the loop. Once the fault is removed, the I300 automatically
reapplies power to the communications loop branch. Figure 2-11, "Two-Wire
Communications Loop," on page 30, illustrates the use of an I300 on a 2-wire
communications loop meeting NFPA Style 4 requirements. Figure 2-13, "4-Wire
Communications Loop," on page 32, illustrates a 4-wire loop meeting NFPA Style 7 requirements.
Note: During a fault condition, the MS-9200 will register a trouble for each device isolated on the loop branch.
In Figure 2-17, a short on any T-tapped branch off an I300 Isolator Module on the communication loop meeting
NFPA Style 4 wiring requirements, will be isolated from all devices installed both upstream of the I300 (Communica-
tion Loop In) and on the continuation of the loop (shown as a dotted line). As an example, if a short were to occur on
Branch A of the first I300 shown, the Isolator Module would disconnect Branch A and its devices from the rest of the
communication loop, allowing all devices connected before and after that I300 to operate normally.
Isolating Two-Wire Communications Loops
FIGURE 2-17:
Communications
Loop In
Branch A
2.8
Module Addressing
Monitor and Control Modules have two rotary decimal switches which are used by the installer to set the module
address. Addresses from 01 to 99 may be set by positioning the left rotary switch to the value of the '10s' digit and the
right switch to the value of the '1s' digit. For example, address 31 would be set by pointing the left switch to 3 and the
right switch to 1 as shown in Figure 2-18.
Module Addressing Switches
FIGURE 2-18:
34
Continuation of the Communication Loop
I300
T-tapped Branches off of the Communications Loop
Document #50428
I300
Branch B
Rev.C1
2/15/99
P/N 50428:C1
Loop In (-)
I300
Loop In (+)
Loop Out (-)
Loop Out (+)
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