Network Communications—N2 Communications Bus
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The N2 Bus may not communicate because the length of the bus is too
long. The recommendation is 1524 m (5000 ft) for each segment and a
maximum distance of 4572 m (15,000 ft) from the farthest N2 device.
The N2 Bus is strictly a daisy-chained bus in which multiple devices are
connected in series. You cannot cut the bus between two devices, add a
T or Y connection, and then connect another device from the connection.
If you do this, signal reflections will result, disturbing normal N2
communication. Make sure no such connections exist.
The N2 Bus must be properly grounded at only one location, preferably at
the NCU. If grounded at two or more locations, a ground loop will be
introduced that will disrupt normal N2 communications.
The N2 Bus wiring at the repeater must be properly and securely
connected. Refer to the
Installing the Repeater
section in this document
for details. The device itself, if defective, can cause N2 communication
problems. For troubleshooting information, refer to the manufacturer’s
literature.
The surge protector may cause N2 communication problems. First, make
sure the surge protector is wired correctly, especially the hard and soft
grounds (Refer to Figures 24-30.) An easy way to tell if the unit is
defective is to simply disconnect the hard ground wire on the protected
side of the surge protector. If communication is restored, the unit is
defective and should be replaced.
Another way is to disconnect the surge protector from the N2 Bus and tape
the loose ends of the bus together, making sure you maintain proper
polarity. If N2 Bus communication resumes, the surge protector is
defective.
The surge protector is not field-serviceable. If found defective, the entire
unit must be replaced.
Checking the
Length of
N2 Bus
Checking for
“T” or “Y”
Connections
Checking for a
Ground Loop
Checking the
Repeater
Checking the
Surge
Protector
