Locked Rotor Amp value is the higher average
current as measured on mechanically blocked
compressor tested under nominal voltage. The
LRA value can be used as rough estimation for
the starting current. However in most cases, the
real starting current will be lower. A soft starter
can be applied to reduce starting current.
The MCC is the current at which the motor
protection trips under maximum load and
low voltage conditions. This MCC value is the
maximum at which the compressor can be
operated in transient conditions and out of
the application envelope. Above this value, the
internal motor protection or external electronic
module will cut-out the compressor to protect
the motor.
The max. operating current is the current when
the compressors operate at maximum load
conditions and 10% below nominal voltage
(+15°C evaporating temperature and +68°C
condensing temperature). Max Oper. A can be
used to select cables and contactors. In normal
operation, the compressor current consumption
is always less than the Max Oper. A. value.
LRA (Locked Rotor Amp)
MCC (Maximum
Continuous Current)
Max. Operating Current.
Winding resistance
Electrical data, connections and wiring
Three phase electrical
characteristics
Compressor model
LRA
MCC
Max. operating current
Winding resistance
A
A
A
Ω
Motor voltage code 4
CH290
260
62
56
0.52
CH485
413
90
89
0.23
Winding resistance is the resistance between
phases at 25°C (resistance value +/- 7%).
Winding resistance is generally low and it
requires adapted tools for precise measurement.
Use a digital ohm-meter, a “4 wires” method and
measure under stabilised ambient temperature.
Winding resistance varies strongly with winding
temperature. If the compressor is stabilised
at a different value than 25°C, the measured
resistance must be corrected using following
formula:
a + t
amb
R
tamb
= R
25°C
_______
a + t
25°C
t
25°C
: reference temperature = 25°C
t
amb
: temperature during measurement (°C)
R
25°C
: winding resistance at 25°C
R
amb
: winding resistance at tamb
Coefficient a = 234.5
General wiring
information
The wiring diagrams below are examples for a
safe and reliable compressor wiring. In case an
alternative wiring logic is chosen, it is imperative
to respect the following rules:
When a safety switch trips, the compressor must
stop immediately and must not re-start until
the tripping condition is back to normal and
the safety switch is closed again. This applies to
the LP safety switch, the HP safety switch, the
discharge gas thermostat and the motor safety
thermostat.
In specific situations, such as winter start
operation, an eventual LP control for pump-
down cycles may be temporarily bypassed to
allow the system to build pressure. But it remains
mandatory for compressor protection to apply an
LP safety switch. The LP safety switch must never
be bypassed.
Pressure settings for the LP and HP safety switch
and pump-down listed in table from section “Low
pressure”.
When ever possible (ie. PLC control), it is
recommended to limit the possibilities of
compressor auto restart to less than 3 to 5 times
during a period of 12 hours when caused by
motor protection or LP safety switch tripping.
This control must be managed as a manual reset
device.
14
FRCC.PC.026.A4.02
Application Guidelines