Johnson Controls Metasys Intelligent Fire Network Technical Manual page 19

Choosing an FN
Communication
Medium
Style 4 Operation
Under the Style 4 operation, the following faults on a FN segment result in
communication loss:
• a single open
• a single wire-to-wire short
• a single wire-to-wire short and open
• a single wire-to-wire short and ground
• a single or open and ground
In addition, the above conditions can cause the IFC panels electrically
beyond the fault to lose communication to the Fire OWS, as well as the
rest of the Metasys FMS system. A single ground does not affect
communication, but can be detected. Each fragment of the network on
either side of a cable fault may reconfigure to permit communication
among the nodes within the fragment.
All network nodes are normally configured for Style 4 in the software.
Network nodes that use both Port A and Port B of the MIB, however, can
be configured for Style 7 in software to pinpoint, when necessary, which
port is having a communication problem. This, however, does not make
the network Style 7.
The communication media choices for the FN include unshielded twisted
pair copper wire, fiber optic cable, or a combination of the two. Both
twisted pair wire and fiber optic cable have distance limitations, and the
procedures differ for determining permissible segment length. For details,
refer to either the Twisted Pair Copper Wire Circuits or the Fiber Optic
Cable Circuits sections that follow.
Twisted Pair Copper Wire Circuits
When using twisted pair copper wire, the cable manufacturer and part
number of the twisted pair wire should be selected to satisfy code and
specific application requirements. Refer to Table 6 for descriptions of
specific cable types used with the FN.
The length of individual circuit segments is limited by attenuation of the
cable selected. The maximum length depends on the selected receiver
threshold setting and is listed in Table 6. The low threshold setting makes
the receiver more sensitive to both signal and noise. The high threshold
setting makes the receiver more immune to noise but requires a stronger
signal, which is equivalent to a shorter distance limit. If the distance
required for a circuit segment is greater than permitted, a Repeater module
(Model RPT-W) must be inserted into the circuit segment at intervals less
than or equal to the length restriction.
IFC Networking—Metasys Intelligent Fire Network 19