Carrier bryant Evolution Connex Control SYSTXBBECC01-C Installation Instructions Manual page 14

It is not mandatory that the above color code be used, but each ABCD
connector in the system MUST be wired consistently.
NOTE: Some outdoor units, typically those with multiple compressor
stages, provide their own low-voltage power source and do not require
the "C" (24VAC common). See the outdoor unit installation instructions
for more information.
ELECTRICAL OPERATION HAZARD
Failure to follow this warning could result in personal injury or death.
Before installing, modifying, or servicing system, the main electrical
disconnect switch must be in the OFF position. There may be more than
one disconnect switch. Lock out and tag switch with a suitable warning
label.
4.4.1. Shielded Wire and Communication Bus
Configuration
If the thermostat wiring will be located near or in parallel with high
voltage wiring, radio, TV or Ethernet wiring, then four conductor,
twisted-pair, shielded cable can be used to reduce or eliminate potential
interference. The shield wire should be connected to the C terminal, or
ground, AT THE INDOOR UNIT, ONLY. The shield wire should NOT
be connected to any terminal at the Evolution Connex Control.
WARNING
!
14
A B C D
A03193