Trane RAUJ-C20, Installation, Operation And Maintenance Manual

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104 SS-SVX11K-EN
Figure 73. W973 master energy controller (MEC)
SENSOR STAT 24 VAC ECONO
HEAT
COOL
HEAT
COOL
T T1 3 4 2 5 1 TR TR W B Y R
C +20 H N
2
3
4
1 2
3
4
1
Voltage Imbalance
Excessive three phase voltage imbalance between
phases will cause motors to overheat and eventually
fail. The maximum allowable voltage imbalance is 2%.
Measure and record the voltage between phases 1, 2,
and 3 and calculate the amount of imbalance as
follows:
% Voltage Imbalance = 100 x [(AV - VD)/(AV)] where:
• AV (Average Voltage) = (Volt 1 + Volt 2 + Volt 3)/3
• V1, V2, V3 = Line Voltage Readings
• VD = Line Voltage reading that deviates the farthest
from the average voltage.
E Ex xa am mp plle e::
If voltage readings of supply power measured 221, 230,
and 227, average volts would be:
• AV = (221 + 230 + 227)/3 = 226 Avg.
• VD = 221
The percentage of imbalance is calculated as follows:
• 100 x[(226 - 221)/226)] = 2.2%
The 2.2% imbalance in this example exceeds the
maximum allowable imbalance of 2.0%. This much
imbalance between phases can equal as much as a
20% current imbalance with a resulting increase in
motor winding temperatures that will decrease motor
life. If the voltage imbalance is over 2%, notify the
proper agencies to correct the voltage problem before
operating this equipment.
Electrical Phasing
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Proper electrical phasing can be quickly determined
and corrected before starting unit by using an
instrument such as Associated Research Model 45
Phase Sequence Indicator, following steps below
• Turn field supplied disconnect switch that provides
power to terminal block 1TB1 to “Off” position
• Verify that the 115 volt control switch (1S2) in the
unit control box is in the "Off" position.
• Connect the phase sequence indicator leads to the
terminal block or to the “Line” side of the optional
factory mounted disconnect switch as follows:
• Black (phase A) to L1
• Red (phase B) to L2
• Yellow (phase C) to L3
• Close the main power disconnect switch or circuit
protector switch that provides the supply power to
the condensing unit.
• Observe the ABC and CBA phase indicator lights on
the face of the sequencer. The ABC indicator light
will glow if the phase is ABC. If the CBA indicator
light glows, open the disconnect switch or circuit
protection switch and reverse any two power wires.
• Restore the main electrical power and recheck the
phasing.
• If the phasing is correct, open the main power
disconnect switch or circuit protection switch and
remove the phase sequence indicator.
P Prre e--S Stta arrtt