Sel 421 - Figure 2.8 Fast Hybrid Control Output Typical Terminals, INT5 (INT8); Figure 2.9 Precharging Internal Capacitance of Fast Hybrid Output Contacts, INT5 (INT8)

U.2.10
SEL-421 Relay User’s Guide Date Code 20090715
Installation
Shared Configuration Attributes
Figure 2.8 Fast Hybrid Control Output Typical Terminals, INT5 (INT8)
Figure 2.9 shows some possible connections for this third terminal that will
eliminate the false pick-up transients when closing an external switch. In
general, you must connect the third terminal to the dc rail (positive or
negative) that is on the same side as the open external switch condition. If an
open switch exists on either side of the output contact, then you can
accommodate only one condition because two open switches (one on each
side of the contact) defeat the precharge circuit.
Figure 2.9 Precharging Internal Capacitance of Fast Hybrid Output
Contacts, INT5 (INT8)
For wiring convenience, on the INT5 (INT8) I/O Interface Board, the
precharge resistors shown in Figure 2.8 are built-in to the I/O board, and
connected to a third terminal. On the INT4 I/O Interface Board, there are no
built-in precharge resistors, and each Fast Hybrid control output has only two
terminal connections.
Main Board I/O
The SEL-421 base model is a 3U chassis with I/O interface on the main board
(the top board). See Figure 2.27 and Figure 2.28 for representative rear-panel
views of the 3U chassis rear panel. There are two options for the main board
depending on the type of contact inputs. The Main Board A I/O interface has
direct coupled contact inputs. The Main Board B I/O interface has
optoisolated contact inputs.
03
1MΩ 1MΩ
02
01
Load
Load
(+)
(+)
(–)
(—)
Precharge circuit
path internal to Fast
Hybrid control output
01
02
02
01
03
03
Courtesy of NationalSwitchgear.com