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SPS IDNet Wiring
Overview
IDNet Wiring
Guidelines
This section describes how the IDNet Channel on the SPS connects to addressable
devices/detectors.
The guidelines governing IDNet wiring guidelines are covered in Chapter 6, IDNet
Installation.
Up to 250 IDNet initiating devices are supported on the SPS IDNet channel. The SPS
supports both Class A (loop) and Class B (string) wiring. Class A wiring is mandatory for
connection to more than 40 devices.
Class A wiring allows IDNet appliances to continue to communicate with the SPS even in
the event of an open circuit somewhere in the loop. Class A wiring requires that two
wires are routed from the SPS to each IDNet appliance, and then back again to the SPS.
Class B wiring allows "T" tapping, and therefore requires less wiring distance per
installation than Class A.
Note that IDNet wiring does not require end-of-line resistors, because each IDNet
appliance communicates directly to the SPS.
Ferrite beads are required on the SPS IDNet cables (refer Figure 5.1).
Shielded cable is recommended in electrically noisy environments.
IDNet cabling should not be run adjacent to other cabling, especially non-fire
system cabling, such as mains.
The limiting factors on the length of the twin core cable connecting the IDNet
devices to the IDNet card are cable capacitance (attenuates the superimposed
coms signal) and resistance (causes voltage drop of the supply voltage and
comms signals).
The maximum capacitance of 0.58uF core to core must also include the mutual
capacitance of core to earth. Shielded cable has a much higher capacitance to
earth.
Rather than do voltage drop calculations, Figure 6-4 can be used to check that
cable limits have not been reached. For a Class A (loop) circuit, cable distance
refers to the full distance around the loop. For a Class B (spur) circuit, cable
distance refers to the distance from the panel to the furthest end of the cable.
Sounder bases and 6 point I/O modules do not draw the alarm load from the
loop, but are powered from separate 24V terminals.
Where devices, e.g. sounder bases, are wired from a 24V source (e.g. supplied
by 24V Aux Power or a NAC), and are in more than 1 zone, the power cable
must also be isolated between zones by a 4090-9117AU Power Isolator Module.
5-19
Continued on next page
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