CHAPTER 3: INSTALLATION PANEL CUTOUTS
B90 LOW IMPEDANCE BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-5
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3.2.1  Rear terminal layout
The relay follows a convention with respect to terminal number assignments, which are three characters long and 
assigned by module slot position, row number, and column letter. Two-slot wide modules take their slot designation from 
the first slot position (nearest to CPU module), indicated by an arrow marker on the terminal block. The figure shows an 
example of rear terminal assignments.
Do not touch any rear terminals while the relay is energized, else death or serious injury can 
result from electrical shock.
The small form-factor pluggable ports (SFPs) are pluggable transceivers. They transmit and receive 
and convert electrical signals to optical signals and vice-versa. They are inserted into the Ethernet 
ports on the CPU module. A photo in the Maintenance chapter shows this plug-in device. Do not use 
non-validated transceivers or install validated transceivers in the wrong Ethernet slot, else damage 
can occur.