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.
EExxaammppllee::
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
WWAARRNNIINNGG
HHaazzaarrddoouuss VVoollttaaggee!!
FFaaiilluurree ttoo ddiissccoonnnneecctt ppoowweerr bbeeffoorree sseerrvviicciinngg ccoouulldd
rreessuulltt iinn ddeeaatthh oorr sseerriioouuss iinnjjuurryy..
DDiissccoonnnneecctt aallll eelleeccttrriicc ppoowweerr,, iinncclluuddiinngg rreemmoottee
ddiissccoonnnneeccttss bbeeffoorree sseerrvviicciinngg.. FFoollllooww pprrooppeerr
lloocckkoouutt//ttaaggoouutt pprroocceedduurreess ttoo eennssuurree tthhee ppoowweerr
ccaann nnoott bbee iinnaaddvveerrtteennttllyy eenneerrggiizzeedd.. VVeerriiffyy tthhaatt nnoo
ppoowweerr iiss pprreesseenntt wwiitthh aa vvoollttmmeetteerr..
WWAARRNNIINNGG
LLiivvee EElleeccttrriiccaall CCoommppoonneennttss!!
FFaaiilluurree ttoo ffoollllooww aallll eelleeccttrriiccaall ssaaffeettyy pprreeccaauuttiioonnss
wwhheenn eexxppoosseedd ttoo lliivvee eelleeccttrriiccaall ccoommppoonneennttss ccoouulldd
rreessuulltt iinn ddeeaatthh oorr sseerriioouuss iinnjjuurryy..
WWhheenn iitt iiss nneecceessssaarryy ttoo wwoorrkk wwiitthh lliivvee eelleeccttrriiccaall
ccoommppoonneennttss,, hhaavvee aa qquuaalliiffiieedd lliicceennsseedd eelleeccttrriicciiaann
oorr ootthheerr iinnddiivviidduuaall wwhhoo hhaass bbeeeenn pprrooppeerrllyy ttrraaiinneedd
iinn hhaannddlliinngg lliivvee eelleeccttrriiccaall ccoommppoonneennttss ppeerrffoorrmm
tthheessee ttaasskkss..
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.
PPrree--SSttaarrtt
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