2.24
SEL-421 Relay Instruction Manual Date Code 20171021
Installation
Relay Placement
Relay Placement
Proper placement of the SEL-421 helps make certain that you receive years of
trouble-free power system protection. Use the following guidelines for proper
physical installation of the SEL-421.
Physical Location
You can mount the SEL-421 in a sheltered indoor environment (a building or an
enclosed cabinet) that does not exceed the temperature and humidity ratings for
the relay.
The relay is rated at Installation/Overvoltage Category II and Pollution Degree 2.
This rating allows mounting the relay indoors or in an outdoor (extended) enclo-
sure where the relay is protected against exposure to direct sunlight, precipita-
tion, and full wind pressure, but neither temperature nor humidity are controlled.
You can place the relay in extreme temperature and humidity locations. The tem-
perature range over which the relay operates is –40° to +185°F (–40° to +85°C,
see Operating Temperature on page 1.16). The relay operates in a humidity range
from 5 to 95 percent, no condensation, and is rated for installation at a maximum
altitude of 2000 m (6560 feet) above mean sea level.
Rack Mounting
When mounting the SEL-421 in a rack, use the reversible front flanges to either
semiflush-mount or projection mount the relay.
The semiflush mount gives a small panel protrusion from the relay rack rails of
approximately 1.1 in. or 27.9 mm. The projection mount places the front panel
approximately 3.5 in. or 88.9 mm in front of the relay rack rails.
See Figure 2.22 for exact mounting dimensions for both the horizontal and verti-
cal rack-mount relays. Use four screws of the appropriate size for your rack.
Table 2.10 Front-Panel LED Option
JMP11, JMP12
a
a
JMP11 Open; JMP12 Closed.
LED Color
BRIDGE
Pins 1 and 3
Pins 2 and 4
Red
BRIDGE
Pins3 and 5
Pins 4 and 6
Green
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