Specifications

Cable Specifications
Installation Handbook, Autroprime Interactive Fire Detection System, 116-P-APRIME-INSTALL/DGB Rev. E, 2011-08-16,
Autronica Fire and Security AS
Page 19
8.3 The Panel Bus Cable Requirements
8.3.1 Characteristic Impedance and Signal Attenuation
When dealing with specification of the Panel Bus cable, the important
issues are the characteristic impedance and the attenuation of the
signal at approximately 100 KHz. These parameters become more
important the longer the cable is.
The parameters are defined by the geometry of the cable. Proper
characteristic impedance is best obtained by a cable with twisted
pairs. For short communication paths (less than approximately 100m)
the characteristic impedance is not that important, and attenuation is
low enough for most cables. However, the twisting improves the
cable’s ability to withstand external interference, and a twisted cable
should be preferred when the cable runs in the vicinity of power
cables and power devices as generators, transformers etc.
Longer paths require twisted pair cable and 100 ohms characteristic
impedance, Cat 5 or similar cable intended for RS485 transmission.
The characteristic impedance shall be (at 100KHz:) 100 ohm +/- 15
ohm. Note that the characteristic impedance has nothing to do with
the resistance of the cable. It is a property related to high-frequency
transmission, regardless of its length. Typical examples are antenna
cable (300 ohm), video cable (75 ohm).
Attenuation is defined by the wire to wire capacitance mostly, as long
as the wire is at least 0.5mm2. The total attenuation of the cable
length must not exceed 9 dB @ 100KHz. If attenuation is not
specified, normally the capacitance is defined. The capacitance
should not exceed the specified value in order to achieve the total
communication length.
8.3.2 High-voltage and Noisy Environments
In high-voltage environments (power plants, electrical machinery etc.)
it is recommended that shielded cable is used. In this case, the
shielding of the cable should only be connected at one end to avoid
ground loops. If high-frequency noise is expected (>10MHz), then
both ends should be connected. This may be present close to radio
transmitting equipment or similar.