ROC364 Instruction Manual
A-2 Lightning Protection Module Rev Jun/05
A.2 Connecting the LPM to Wiring
There is a one-to-one correspondence between the LPM terminals and the terminals of the I/O channel
being protected. If you are connecting field wiring to the LPM, refer to the I/O wiring information in this
instruction manual.
NOTE: The LPM module provides sockets for a plug-in range (scaling) resistor. These sockets,
which are internally connected to the module’s middle and right-most screw terminals, must be
used when installing a range resistor for a built-in Analog Input channel. For an Analog Input
module or any other module using a scaling resistor, either the sockets on the I/O module or on
the LPM may be used for the scaling resistor.
The LPM module provides a ground wire for connection to the enclosure ground bar or ground lug. The
enclosure ground bar or ground lug must in turn be connected to a good earth ground. Do not use the
power system ground for this connection.
To add an LPM to protect an I/O module, perform the following steps.
If you are installing an LPM on a ROC currently in service, and there is a field device connected
to the I/O channel that will receive the LPM, make sure the field device will not be left in an
undesirable state when it is disconnected from the ROC.
Do not use the LPM with a 120 volt ac signal on a DO Relay Module.
1. Unplug the field wiring module block from the channel for which the LPM is going
to be installed.
2. Plug the LPM into the field wiring terminal block socket located in step 1.
3. Connect the LPM ground wire to the ground bus bar. The ground bar must be connected to a
good earth ground. Do not use the power system ground for this connection.
4. Transfer any field wiring from the unplugged module block to the built-in termination block on
the LPM.
A.3 Troubleshooting and Repair
The Lightning Protection Modules function by shunting the high voltage transients through gas
discharge tubes to the ground lead. In the event of an I/O signal failure, verify the signal is not
interrupted by the LPM.
1. Before removing an LPM, make sure all devices and processes remain in a safe state.
2. Remove the LPM and disconnect the field wiring.
3. Remove any range resistors from the LPM.
4. With a digital multimeter, verify continuity through each connector socket to the corresponding
field wiring terminal. If there is no continuity, replace the LPM.
5. With a digital multimeter, check each of the input terminals for continuity to the ground lead. If
the test shows continuity to the ground lead, replace the LPM.
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