VMA1400 Series Overview and Engineering Guidelines Technical Bulletin 12
N2 Bus Rules
The N2 Bus is the interface between a supervisory controller
(Metasys Network Control Module [NCM] or N30) and all application
specific controllers in a Metasys Network. The VMA is
self-terminating in that there are no End-of-Line (EOL) jumpers to set.
However, you must set one EOL for each N2 Bus, usually at the NCM
or N30. Table 2 summarizes the rules for installing the N2 Bus.
Table 2: N2 Bus Rules
Category Rules/Maximums Allowed
General
Only one NCM or N30 per N2 Bus
Only daisy-chained devices
Maximum Number of Devices
100 devices per NCM or 50 devices per N30
50 devices per repeater*
Two repeaters cascaded
Line Length and Type
1500 m (5000 feet) between repeaters
4500 m (15,000 feet) maximum length
(3 segments of 1500 m [5000 feet] each)
0.6 mm (24 American Wire Gauge [AWG])
twisted pair minimum
(stranded 0.8 mm [22 AWG] twisted pair or
heavier recommended)
Terminations
Two EOL devices per each segment that is
longer than 100 m (330 ft)
One EOL device at the controller for all
segments regardless of length (required)
* Add repeater after 49 devices. Count each repeater as one device.
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