CTV-PRB004-EN
11
Chiller Selection and Electrical Specification
F. Minimum circuit ampacity (MCA).
This term appears on the chiller nameplate and is used
by the electrical engineer to determine the size and number of conductors needed to bring power
to the starter.
… with this number rounded up to the next whole number. Said another way, the MCA is
125 percent of the motor design primary RLA (incoming line) plus 100 percent of the amperage of
other loads (sump heater, oil pump, purge, etc.).The MCA is listed on the chiller selection report.
Power cable sizes and conduits are discussed in
“Electrical System–PowerWire Sizing,” p. 56
. If the
AFD is a remote, free-standing AFD, the MCA will be based on the compressor motor RLA.
G. Maximum overcurrent protection (MOP or MOCP).
The MOP appears on the chiller
nameplate. The electrical engineer often wants to know the MOP when the chiller is selected for
sizing fuses and upstream circuit breakers. Understand that the MOP is a maximum,
NOT
a
recommended fuse size. Improperly sized circuit breakers or fuses can result in nuisance trips
during the starting of the chiller or insufficient electrical protection. MOP is also
NOT
used to size
incoming power wiring—the MCA is used for this purpose.
MCA = 1.25 x (Primary RLA [incoming line])+
(
4000
)
volts
motor
CTV-PRB004.book Page 11 Sunday, December 18, 2011 6:39 PM
