Terminating A Bus; Lightning Transient Suppression - Emerson PACSystems VersaMax User Manual

PACSystems VersaMax Genius Network Interface User Manual
GFK-1535D
4. When inserting two wires into the same terminal, the wire size
2.12.1

Terminating a Bus

If the bus terminates at the NIU, connect a 75, 100, 120, or 150-ohm
terminating resistor across Serial 1 and Serial 2. The use of a ferrule is
recommended to crimp each resistor lead to the corresponding serial
line. If ferrules are not used, twist each resistor lead with the
corresponding serial line and solder them together before inserting the
wires into the terminal.
Figure 33: Terminating a Bus
2.12.2

Lightning Transient Suppression

Running the bus cable outdoors or between buildings may subject it to
lightning transients beyond the 1,500-volt transient rating of the system.
Installing cable underground reduces the probability of a direct lightning
strike. However, buried cables can pick up hundreds of amperes of
current when lightning contacts the ground nearby.
Therefore, it is important to protect the installation by including surge
protectors on underground data lines. The cable shields should be
grounded directly. Surge suppressors and spark gaps should be used to
limit the voltage that might appear on the signal lines. It is recommended
to install two (only) silicon surge suppressors or spark gaps to control
transients of 1 to 25 Kilovolts from 100 to 1000 amps or more. These
devices should be installed close to the entrance of the bus to the
outdoors.
In extreme situations, such as isolated power systems, additional
protection against lightning damage should be provided. Such
Installation
must be 0.86mm2 (18 AWG) or smaller. Both wires should be the
same size and type. Do not mix stranded with solid wire in the
same position.
Section 2
Jan 2023
42