Elkron FAP54, Installation Manual

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24 FAP54 Installation
4.2 OPERATION AND CHARACTERISTICS OF CONNECTION WITH CLASS A
The loop connection ensures the integrity of the system also in case of malfunctioning due to the opening or short
circuit of the detection line.
In normal operating conditions the control panel communicates with the detectors by sending a code from both loop
sides, therefore a possible line opening does not affect communication: in such a case, the control panel gives notice
of the occurred opening, but the system keeps on working. In the event of line short circuit, the short circuit insulators
fitted on the line devices allow the insulation of the line section affected by the short circuit, without losing any devices.
Should the short circuit affect a device, the insulators will isolate the line in order to automatically exclude the device
and signal, in addition to the detected short circuit, also a fault due to lack of communication with the isolated device.
For example, with reference to Figure 2, if a short circuit occurs between device 2 and device 3, the action of the
insulators enables the system to isolate the line section between the devices under consideration.
Device 2 will be powered by “side A” of the line module, while device 3 will be powered by “side B” of the line module.
No device will be lost and the short circuit will be isolated.
Instead, if the short circuit occurs on device 2, the insulators will isolate the line section upstream (between devices 1
and 2) and downstream (between devices 2 and 3).
Device 1 will be powered by “side A” of the line module, while device 3 will be powered by “side B” of the line module.
In this case device 2, where the short circuit occurred, will be lost.
The control panel will signal, in addition to the detected short circuit, also the lack of communication with device 2.
In class A connections no “T” shunting is admitted.
Loop line electric characteristics
•
Suggested cable: 2 x 1.5 mm² shielded.
•
Max loop line total length: 2000 m
•
Cable total resistance: less than 100 Ω
To find out the line cable resistance, short circuit one end of the two wires and measure the opposite end with an
ohmmeter.