Date Code 20010518
Installation
3-3
SEL-2020 Instruction Manual
modems enable you to synchronize more precisely devices capable of receiving IRIG-B time
code, even with a fiber optic communication link.
The IRIG-B signal includes code for day-of-year and time-of-day. It does not include a code to
identify the year. To ensure the device calendar is set to the proper year, you need to set the date
on each device receiving an IRIG-B signal. Most SEL relays store the year for the set date with
the relay settings in nonvolatile memory, so once the date is properly set, the relay will maintain
the proper year even if relay power is cycled off and on.
Communication Circuit Connections
The SEL-2020 Communications Processor is equipped with sixteen rear panel serial communica-
tion ports, labeled “PORT 1” through “PORT 16”, and one front panel serial communication
port, labeled “PORT F”. The data connection for each SEL-2020 serial communication port uses
EIA-232 standard signal levels in a 9-pin, subminiature “D” connector (see Figure 3.1 and Table
3.1). EIA-232 interfaces are supported by almost all modern relays, meters, computer, and
communications devices.
Figure 3.1: 9-Pin Connector Pin Number Convention (female chassis connector, as viewed
from outside panel)
WARNING
!
Do not rely upon pins 5 and 9 for safety grounding, because their
current-carrying capacity is less than control power short circuit
and protection levels.
The communication circuits are protected internally by low-energy, low-voltage MOVs and
passive RC filters.
You should keep the length of the communication cables as short as possible to minimize
communication circuit interference and also to minimize the magnitude of hazardous ground
potential differences that can develop during abnormal power system conditions. See the next
subsection, titled “Communication Cables” for additional details and restrictions.
Note:
When an internal modem is installed, you must use the telephone connector on Port 8,
not the 9-pin connector. Conversely, if the internal modem is not installed, you must use
the 9-pin connector because the telephone connector on Port 8 will not be functional.
Summary of Contents for SEL-2020
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