Dry Contact use note of caution
Page 27
Auxiliary Input Control and Multiple HVAC Control
Potential Phasing Problems
110vac
Isolation Relay
Coil
CK 1
R
Thermostat
CK 1
R
Thermostat
CK 1
R
Thermostat
Additional relays may be used. Relay coils must be wired in parallel.
Diagram A- Auxiliary Control
When using the auxiliary input (CK1 & R) or controlling multiple HVAC units with a
single thermostat, it is possible to encounter transformer phasing problems that will
interfere with thermostat operation. Connecting transformers that are not phased
correctly may result in a direct short, which could damage transformers and/or the
thermostat. Phasing problems are likely if the units share a common ground with
secondary grounded transformers.
CAUTION
WARNING
SOLUTION:
If possible, phase all HVAC units together. If phasing is impractical,
isolation relays may be used to isolate the transformers. To isolate the auxiliary
input, use a separate transformer for the auxiliary control device, usually a time clock.
Connect the device to an isolation relay coil. Connect one set of isolated contacts to
each thermostat at
CK1
and
R
. See diagram A.
