RTU Open 31
Wiring diagram for optional enthalpy sensor mounted in the return air for differential enthalpy:

Wiring a status switch

Filter - Part #33CSFS-01 or field-supplied
Fan status - Part #33CSAS-01 or field-supplied
Filter and/or fan status switches may be installed to provide a Dirty Filter indication or Fan Running status.
Wiring specifications
Cable from sensor to controller: If <100 ft (30.5 meters) 22 AWG, unshielded
If >100 ft (30.5 meters) 22 AWG, shielded
Maximum length: 500 feet (152 meters)