Date Code 20011026 Installation 6-3
SEL-321/321-1 Instruction Manual
Note: Output contacts OUT1 - OUT28 and ALARM on relays equipped with interrupting-duty
contacts are polarity dependent (note the “+” symbol on these contacts).
As an example, consider the connection of terminals 217 and 218 (output contact OUT1)
in a circuit:
Terminal 218 (+) has to be at a higher voltage potential than terminal 217 in the circuit.
Standard output contacts are not polarity dependent (they do not have a “+” symbol).
Optoisolated inputs IN1 through IN16 are not polarity dependent.
Current input connector (terminals 101-108):
• Contains current transformer shorting mechanisms
• Accepts wire size AWG 16 to 10 (special tool required to attach wire to connector)
• Can be ordered prewired
Ground connection (terminal 124): tab size 0.250 inch x 0.032 inch, screw size #6-32.
Frame Ground Connection
You must connect the grounding terminal (#124) labeled “GND” on the rear panel to a frame
ground for proper safety and performance. Use 12 AWG (or heavier) wire, less than 2m (6 feet)
long for this. This terminal connects directly to the internal chassis ground of the instrument.
Power Connections
The terminals labeled “POWER” on the rear panel must be connected to a power source that
matches the power supply (PWR SUP) characteristics specified on the rear-panel nameplate of
your SEL-321 Relay. Control power passes through these terminals to the fuse(s) and a toggle
switch, if installed. These terminals are isolated from the chassis ground. If you provide a dc
power source, you must connect the source with the proper polarity as indicated by the “+” and
“−” symbols on the power terminals. The SEL-321 Relay internal power supply has low power
consumption and a wide input voltage tolerance. See General Specifications in Section 2:
Specifications for complete power supply information.
Secondary Circuit Connections
The SEL-321 Relay presents a very low burden to the secondary potential and current circuits. It
requires three phase, four-wire (wye) potentials (VA, VB, VC, and N) and three currents (IA, IB,
IC) from the power system transformer secondaries. See Figure 6.17. Check the specified
rotation and nominal voltage, current, and frequency on the rear-panel nameplate to ensure
proper application prior to connection. To verify these connections, trigger an event report using
the TRIGGER command (see Section 3: Communications). Analyze it using the SEL Direction
and Polarity Check Form included at the end of this section.
Control Circuit Connections
Refer to Figure 6.18 and Figure 6.19.
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