Date Code 20011026 Interface Board Specifications I-1
SEL-321/321-1 Instruction Manual
APPENDIX I: INTERFACE BOARD SPECIFICATIONS
INTRODUCTION
The SEL-321 Relay is available with one or two interface boards for application flexibility. The
number of inputs, number of outputs, operating speeds, interrupt capabilities, and operation
configuration vary depending on the interface boards. This appendix describes the interface
boards and shows partial rear-panel diagrams for each.
Note: The interface boards are not interchangeable with each other on a two I/O board relay.
Table I.1: Interface Board Types
Screw Terminal
I/O Board Inputs Outputs
Interface 1 8 16 Standard Shared-Terminal
Interface 2* 8 12 Standard Independent
Interface 5 8 8 Fast High Current Interrupting
Plug-In Connections
I/O Board Inputs Outputs
Interface 1 8 16 Standard Shared-Terminal
Interface 2 8 12 Standard Independent
Interface 6 8 12 High Current Interrupting
* Interface board 2 is listed as option 3 on the screw terminal ordering information sheet.
INTERFACE BOARD 1 (16 OUTPUTS, 8 INPUTS) - SCREW TERMINAL OR PLUG-IN
CONNECTIONS
Optoisolated Inputs
All eight control inputs are dry optoisolated inputs and are not polarity dependent. The screw
terminal version comes with standard fixed inputs while the plug-in version has fixed level-
sensitive inputs. The nominal rated control voltage of 24, 48, 125, or 250 Vdc must be specified
when ordering. To assert an input, apply control voltage to the terminals assigned to that input.
Each input is individually isolated, and a terminal pair is brought out for each input. There are
no internal connections between inputs. The inputs will assert within 2 ms and draw
approximately 4 mA of current at nominal voltage. For further information, see General
Specifications in Section 2.
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