Installation, Operation and Maintenance Manual
VariCool EZ-Fit
22
Subject to change without notice.
Voltage Unbalance
Voltage unbalance occurs when the RMS line voltages on
a 3-phase power supply are unequal Voltages are never
balanced between phases, but if the level of the unbalance
becomes excessive it will create problems for not only
motors but also controls
The maximum desirable voltage unbalance is 20%
When testing for voltage unbalance, the phase-to-phase
voltages should be measured rather than the phase-to-
neutral voltages since 3-phase motors are connected across
phases Use the following formula to determine the percent
of voltage unbalance:
Percent Voltage Unbalance = 100 x (Maximum Voltage
Deviation / Average Voltage)
Example:
Phase-Phase voltages
A-B = 479V
B-C = 472V
C-A = 450V
Average Voltage = (479 + 472 + 450) / 3 = 467 Maximum
Voltage Deviation from Average =
467 - 450 = 17 (Must always be positive) Voltage Unbalance
= 100 x (17/467) = 36%
In this example the percent of voltage unbalance exceeds the
desired maximum of 2% Additional checks should be made
at the unit disconnect to confirm the values Use accepted
industry practices to check or test the quality of the power
supply Often, it is just a matter of repairing malfunctioning
equipment or redistributing loads to improve the unbalance
ELECTRICAL HAZARD
Conduit is not an acceptable grounding
source A separate ground conductor must
be connected from Earth Ground to the
factory supplied grounding lug internal to
the unit
Transformer
Dual voltage units, 208/230, are wired from the factory
for the 208 volt power supply If the power supply will be
consistently above 220 volts the transformer should be
wired on the 230 volt tap
If no cause can be located and resolved for the unit power
supply, the building manager or owner should be notified of
the issue to get the proper power supplied to the unit
High Duct Static Pressure Switch
A high duct static pressure switch is factory installed on a
unit configured for a multi-zone VAV application The high
static pressure switch is a manual reset type Its purpose is
to protect the ductwork in an event that all VAV boxes close
and the call for the unit operation over pressurizes the duct
work The duct static switch requires field tubing installation
The tubing must be mounted in the supply (+) side of the
duct work and external to cabinet pressure (-) There is an
adjustment on the switch to set the trip point in “WC It is
accessible inside the switch by removing the 2 front screws
Simply adjust the inner adjustment screw by hand or with a
flat screw driver and align the red band with the “WC line
you wish the switch to trip at
If this failure signal is sent back to the Marvel Premium
controller, the unit will shut down Adjustments should be
verified with a manometer or magnehelic
Low Voltage Control Devices
Low voltage control devices are located internal to the
evaporator section Wiring and tubing are factory provided
for these items Snap together the multi-pin connector
The multi-pin plug and receptacle only fit together in one
direction Route the tubing to the appropriate low voltage
control device in the control box and connect to the switch
For dual module configurations, there will be connectors in
each module
Wall Display
The Wall Display is a shipped loose item along with 100
feet of interconnecting cable Refer to the
Marvel Premium
installation instructions for specific mounting instructions,
details and precautions
INFORMATION
Variable Frequency Drive (VFD) - An
unbalanced power supply to a variable
frequency drive (VFD) may result in
nuisance tripping and 3rd harmonic
currents
