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Wiring a Signaling Line Circuit (SLC)
2-48 AFP-300/AFP-400 Installation PN 50253:C1 05/22/97
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Use a loop Isolator Module (ISO-X) to protect critical elements of the SLC from faults
on other branches or sections of the SLC. The ISO-X continuously monitors the circuit
connected to terminals 3 (–) and 4 (+). Upon power-up, an integral relay latches. The
ISO-X periodically pulses the coil of this relay. A short circuit on the SLC resets the
relay. The ISO-X detects the short and disconnects the faulted SLC branch by opening
the positive side of the loop (terminal 4). This isolates the faulty branch from the
remainder of the loop. Once the fault is removed, the ISO-X automatically reapplies
power to the SLC branch.
You can connect a maximum of 25 devices between isolator modules. During a fault
condition, the control panel registers a trouble condition for each addressable device
which is isolated on the SLC segment or branch.
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A short circuit on the SLC Style 4 branch (connected to ISO-X terminals 3 and 4)
causes the branch to be disconnected and isolated from the remainder of the SLC. This
prevents a communication problem with all other addressable devices on the branches
(labeled “Continuation of the SLC” in Figure 2-67) and all addressable devices on the
isolated branch will report a trouble condition at the CPU.
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