Johnson Controls Metasys Intelligent Fire Network Technical Manual page 16

Choosing a
Wiring Style
16 IFC Networking—Metasys Intelligent Fire Network
To meet the UL 864 Listing, the FN must be wired according to
either NFPA Style 7 (Class A) or NFPA Style 4 (Class B)
standards. The difference between the two styles is evident when a single
break or short occurs. A Style 7 circuit will provide an alarm indication
with a single open, a single ground, a wire-to-wire short, or an open and a
ground, because the communication circuit forms a loop (Figure 2). In
other words, with a single fault on the circuit, there is an alternate path for
communication between nodes. A Style 4 will provide an alarm with a
single ground fault, but may not provide an alarm with any of the other
fault types on the circuit and will not communicate with any nodes that are
attached on the network beyond the single break or short (Figure 3).
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 1
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 6
Figure 2: Style 7 Communication with a Single Break
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 1
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 6
Figure 3: Style 4 Communication with a Single Break
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 2
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 5
With a single open,
single ground, a
wire-to-wire short,
or an open and a ground,
all network nodes can still
send an alarm to the
Fire OWS and other nodes.
Network 1
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 2
Network 2
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 5
With a single break
communication is
severed, Nodes 5 and 6
can no longer communicate
with Nodes 1-4 and additional
communication faults may occur.
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 3
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 4
Style7
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 3
I N TELLI G EN T FI R E D E TEC TI O N A N D A LA R M S YSTEM
)
Node 4
style4