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2.35
Date Code 20171021
Instruction Manual
SEL-421 Relay
Installation
Connection
Connectorized
For the Connectorized SEL-421, order the wiring harness kit, SEL-WA0421. The
wiring harness contains four prewired connectors for the relay current and volt-
age inputs.
You can order the wiring harness with various wire sizes and lengths. Contact
your local Technical Service Center or the SEL factory for ordering information.
Perform the following steps to install the wiring harness:
Step 1. Plug the CT shorting connectors into terminals #
Z01
through #
Z06
for
the IW inputs, and #
Z07
through #
Z12
for the
IX
inputs, as appropriate.
Odd-numbered terminals are the polarity terminals.
Step 2. Secure the connector to the relay chassis with the two screws located
on each end of the connector.
When you remove the CT shorting connector, pull straight away
from the relay rear panel.
As you remove the connector, internal mechanisms within the
connector separately short each power system current transformer.
You can install these connectors in only one orientation.
Step 3. Plug the PT voltage connectors into terminals #
Z13
to #
Z18
for the VY
inputs, and #
Z19
to #
Z24
for the VZ inputs, as appropriate.
Odd numbered terminals are the polarity terminals. You can install
these connectors in only one orientation.
Control Circuit Connections
You can configure the SEL-421 with many combinations of control inputs and
control outputs. See
for information about I/O configurations. This subsection provides
details about connecting these control inputs and outputs. Refer to
,
for representative rear-panel screw-terminal con-
nector locations.
Control Inputs
NOTE:
The combined voltages
applied to the IN
nnn
and OUT
nnn
terminals must not exceed 600 V (rms
or dc).
lists the control inputs available with the SEL-421, and notes that some
are Direct-Coupled, and some are Optoisolated.
Direct-Coupled
Direct-coupled control inputs are polarity-sensitive. These inputs use direct-cou-
pled circuitry, and have terminal markings to indicate polarity: a
+
mark appears
for each input. Connect the positive sense of the control input to the
+
terminal.
Although you cannot damage these inputs with a reverse polarity connection, a
reverse polarity connection will cause the relay internal A/D converter to mea-
sure the input voltage incorrectly and the relay will no longer detect input
changes (see
).
Optoisolated
Optoisolated control inputs are not polarity sensitive. These inputs respond to
voltage of either polarity, and can be used with ac control signals when properly
configured.
Summary of Contents for SEL-421-4
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