GE EST iO64 Technical Reference Manual page 74

Chapter 2: Installation and wiring
Class A wiring (Style 6)
–
Loop SEC
+
–
Loop PRI
+
Loop card
Class A wiring (Style 7)
–
Loop SEC
+
–
Loop PRI
+
Loop card
Data line
Loop card LEDs
There are three LEDs on the card that indicate loop communication
status. Primary is the primary communication circuit. Secondary is
the Class A return communication when wiring is Class A. Comm is
overall loop communication.
Loop card LEDs
64
Loop Loop
device device
Data line
Loop devices
with isolator base
Isolator Loop
module devices
UL/ULC listed enclosure
Comm
Secondary
Primary
Isolator
module
EST iO64 and iO500 Technical Reference Manual