6-2 Installation Date Code 20000421
SEL-251, -2, -3 Instruction Manual
The communications circuits are protected by low-energy, low-voltage MOVs and passive RC
filters. You can minimize communications-circuit difficulties by keeping the length of the
EIA-232 cables as short as possible. Lengths of twelve feet or less are recommended, and the
cable length should never exceed 100 feet. Use shielded communications cable for lengths
greater than ten feet. Modems are required for communications over long distances.
Route the communications cables well away from the secondary and control circuits. Do not
bundle the communications wiring with secondary or control circuit wiring. If these wires are
bundled, switching spikes and surges can cause noise in the communications wiring. This noise
may exceed the communications logic thresholds and introduce errors. The IRIG-B clock cable
should also be routed away from the control wiring and secondary circuits.
Jumper Selection
Jumpers JMP103, JMP104, and J6 are on the front edge of the main board. They are easily
accessed by removing the top cover or front panel. Jumpers JMP3 and soldered wire jumpers
JMP4 through JMP11 are toward the back of the main board and are accessed by removing the
top cover.
EIA-232 Jumpers
J6 provides EIA-232 baud rate selection. Available baud rates are 300, 600, 1200, 2400, 4800,
and 9600. To select a baud rate for a particular port, place the jumper so it connects a pin
labeled with the desired port to a pin labeled with the desired baud rate.
Caution: Do not select two baud rates for the same port. This can damage the baud rate
generator.
Password Protection Jumper
Put JMP103 in place to disable password protection. This feature is useful if passwords are not
required or when passwords are forgotten.
OPEN/CLOSE Command Enable Jumper
With jumper JMP104 in place, the OPEN and CLOSE commands are enabled. If you remove
jumper JMP104, OPEN and CLOSE command execution results in the message: "Aborted."
A4 Output Contact Jumper
With jumper JMP3 in the A4 position, the A4 output contact operates per setting A4(2346).
With jumper JMP3 in the ALARM position, the A4 output contact operates with the ALARM
output contact.
Output Contact Soldered Wire Jumpers
All the output contacts can be configured as "a" or "b" contacts with soldered wire jumpers
JMP4 through JMP11 (each jumper has positions A and B). The output contact/soldered wire
jumper correspondence is as follows:
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