Schweitzer Engineering Laboratories SEL-2020 - Communications; Modems

3-6 Installation Date Code 20010518
SEL-2020 Instruction Manual
Table 3.2: Communication Cables for Devices Attached to SEL-2020 (continued)
SEL
Cable #
Connect SEL-2020 to:
Remote Connector
(on cable)
Port
Type
RTS/CTS
Supported
IRIG-B
Included
C282 9-pin DTE devices:
Tasnet 9-pin DTE,
Beckwith M3430
Dranetz SER
DB-9P DTE yes no
C285 9-pin DCE with flow control:
ABB 9-pin PONI Module (DCE),
ABB FOCUS Data Module
DB-9P DCE yes no
C339 9-pin Round Con-X-All devices w/ IRIG:
SEL-100 Series Relays/SEL-PRTU
9-pin Con-X-ALL
(male), 9-pin Con-X-
ALL (male)
N/A yes yes
The following list provides additional rules and practices you should follow to ensure successful
communication using EIA-232 serial communication devices and cables:
• 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.
• EIA-232 communication cable lengths should never exceed 50 feet, and you should
always use shielded cables for communication circuit lengths greater than 10 feet.
• Modems are required for communications over long distances and to provide isolation
from ground potential differences between device locations.
• Route communication cables well away from power and control circuits. Switching
spikes and surges in power and control circuits can cause noise in the communications
circuits if not adequately separated.
• Lower baud rate communication is less susceptible to interference and will transmit
greater distances over the same medium than with higher baud rates. You should use
the lowest baud rate that provides adequate data transfer speed.
COMMUNICATIONS
This subsection describes how you can optimize the communications interface between the
SEL-2020 and other devices it will communicate with.
Modems
If electrical interference is a problem, consider using point-to-point fiber-optic modems to
provide electrical isolation and noise immunity. We recommend the SEL-2810 Fiber-Optic
Modem for these applications. The connection between the SEL-2020 and the modem is EIA-
232. The connection between the remote modem and the remote device is also EIA-232. Optical
fibers connect the two modems.