FANUC Robotics America GFK-1535A - Manual (Page 38)

GFK-1535A Chapter 2 Installation 2-19
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 totally-isolated power systems, additional protection
against lightning damage should be provided. Such suppressors should be installed
from incoming power leads to ground.
Adding Suppression at the Communications Line
For an individual NIU, suppression can be supplied by connecting two small metal
oxide varistors (MOVs) from Serial 1 and Serial 2 to the Shield Out terminal:
S1
S2
SHLD IN
SHLD OUT
(bus cable not shown)
MOVs
Suitable MOVs include Harris part number V220MA2A, Panasonic ERZ-
CO5FK221U, and Siemens 505K140. If necessary, higher energy-rated devices can
also be used.
The use of a ferrule is recommended to crimp each MOV lead to the corresponding
serial line. If ferrules are not used, twist each MOV lead with the corresponding
serial line and solder them together before inserting the wires into the terminal
block.
It is important to be sure that the MOV leads do not cause any shorts between the
serial data and shield connectors.