C-2
Appendix C
Date Code 990714
SEL-2BFR, -2/BFR Instruction Manual
SEL-BFR I
NSTALLATION
Mounting
The relay mounts by its front vertical flanges in a 19" vertical relay rack. Use four #10 screws for
mounting.
Frame Ground Connection
Connect the terminal marked GND (35 or 36) on the rear panel to frame ground for safety and
performance. These terminals connect directly to the chassis ground of the instrument.
Power Connections
Connect terminals (44) and - (45) on the rear panel to a source of control voltage.
Control power passes through these terminals to a fuse and toggle switch, if the unit has one.
The power continues through a surge filter and connects to the switching power supply. Control
power circuitry is isolated from the frame ground.
Secondary Circuits
The relay presents a very low burden to the secondary current and potential circuits. Each
current and voltage circuit is independent of the other circuits; there is no interconnection of
current or voltage circuits inside the instrument.
The relay requires difference-voltage potentials that must be obtained from voltage transformers
on both sides of the circuit breaker if flashover and thermal protection functions are to be used.
Control Circuits
The control inputs are dry. For example, to assert the 52A input, you must apply control voltage
to the 52A input terminals. Each input is individually isolated, and a terminal pair is brought out
for each input. There are no internal connections between control inputs.
Control outputs are dry relay contacts rated for tripping duty. A metal-oxide varistor protects
each contact.
Communications Circuits
Connections to the two EIA-232 serial communications ports are made via the two nine-pin
connectors labeled PORT 1 and PORT 2 on the rear panel.
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.
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