Tyco 4100U installation manual Wiring to IDNet Devices, Continued on next page

Wiring to IDNet Devices

Overview

Guidelines

Up to 250 IDNet slave devices, such as smoke detectors and manual call points, can be connected to the IDNet card using Class A (loop) or Class B (line) wiring, with the following restrictions.

Class A wiring allows the devices to communicate with the IDNet card even in the event of an open circuit somewhere in the loop. Class A wiring requires that two wires are routed from the IDNet card to each IDNet device, and then back again to the IDNet card. Under AS1670.1 every group of 40 devices (or less) must be separated by a Comms Isolator.

Class B wiring allows “T” tapping, and therefore requires less wiring distance per installation than Class A. IDNet wiring does not require end-of-line resistors, because each IDNet device communicates directly to the IDNet card. A maximum of 40 devices is allowed to be connected this way.

See Appendix F for a list of compatible devices and their ratings.

•Use ferrites. See Fig 7.1.

•Shielded cable is recommended in electrically noisy environments.

•IDNet cabling should not be run adjacent to other cabling, especially non-fire system cabling, e.g. mains.

•The limiting factors of the 2 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. The latter is greatly increased when shielded cable is used.

•Rather than do voltage drop calculations (see notes following), the following simplified rules are applied.

•Allow a maximum of 40Ω to any device (Class B), and in any loop (Class A) with 125 devices or less.

•Allow a maximum of 20Ω in any loop with 250 devices.

•Linear de-rating between 40Ω and 20Ω may be applied between 125 devices and

250 devices. Use RL = 20Ω x (1 + (250-n)/125) where RL is the allowable line resistance and n is the number of devices used. E.g. for 200 devices the maximum resistance allowed may be extended from 20Ω to: 20Ω + 20Ω x (250

– 200) / 125 = 28Ω

•Use the resistance specifications that apply to the cable being used. The values used in this manual allow 39Ω per km for 2 core of 1 mm2 for copper wire at

49°C. (A commonly used value is 34Ω per km for 2 core of 1 mm2 at 20°C). See Table 8.1. Note that this includes both cores.

•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.

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