INSTALLATION & OPERATIONS GUIDE | MICROSET 4
© Honeywell LT-MS4IOG Rev. 04 | Revised October 2015
16
Terminating MS/TP LAN cabling
IMPORTANT
Always use communications grade connectors, such as 3M Scotchlok or equivalent, when splicing pigtails
with LAN cabling.
Grounding the MS/TP LAN shield
Proper shield grounding of the cabling can help minimize the risk of communications problems and
damage to equipment because of transient voltage spikes (for example, lightning strikes).
Follow these guidelines for grounding cable shields:
• Each segment must have a single point of shield ground, as close to the middle of the cabling run
as possible (see Figure 10).
• Do not ground the shield directly to a Microset 4 wire.
• Never ground both ends of a shield because differences in potential between the grounds may
induce current on the shield, causing interference.
• At connecting termination points, tie the shield through with a wire nut.
• At ungrounded, exposed shield points (the end of a segment), tape back the shield to the wire
jacket or, for optimum transient shunting, use 100V gas discharge tubes or 120V MOVs between
the shield and ground. See Figure 10.
Figure 10
Shield drain termination and tie through.
Terminating resistors
At the last device on each end of the MS/TP segment, matched terminating resistors wired across MS/
TP+ and MS/TP– are required for signal integrity.
Optimum segment performance typically requires “tuning,” a process by which the value of the
terminating resistors is selected based on the wave form of signals on the segment. View wave forms
using an industrial scope meter. The goal is to have as square a wave form as possible with an
amplitude greater than 200 mV. Resistors affect the wave form as follows:
• When the resistance value decreases, the amplitude of the wave form decreases and becomes
more square.
• When the resistance value increases, the amplitude of the wave form increases and becomes less
square.
Terminating resistors
Matched resistors required at each end of segment bus wired across (+) and (–). Use matched
precision resistors rated ¼W ±1% / 80–130 Ohms. Smoke control applications with the VAV-SD-S
or the VLC-1188-S may require UL-864 listed terminating resistors.
Shield grounding
Ground shield drain wire at single point earth (panel) ground,
not
Microset 4
ground
. Tape off
shield drain wire at other end. Tie shield drain wire through at each MS/TP Microset 4.
Table 4
MS/TP LAN facts (Continued)
Shield drain may be taped back to jacket or routed through MOV or gas discharge tube to ground.
T
T
T
T
T
T
T
T=Shield Tie Through
VLC
MS4-TH-
MSTP
MS4-TH-
MSTP
MS4-TH-
MSTP
MS4-TH-
MSTP
VLC
VLC
VLC
(Optional) 120V MOV
OR
100V Gas Discharge Tube
(Optional) 120V MOV
OR
100V Gas Discharge Tube
ACM
