User Guide

Application guidelines
22 AB237986441643en-US0701
Compressor models SM/SZ084 - 090 - 100
- 110 - 112 - 120 - 124 - 147 - 148 - 161 have
been provided with an internal overload motor
protection to prevent against excessive current
and temperature caused by overloading,
low refrigerant ow phase loss or incorrect
motor rotation. The cutout current is the MCC
value listed in section “Three phase electrical
characteristics”.
The protector is located in the star point of the
motor and, should it be activated, will cut out all
three phases. It will be reset automatically.
While not compulsory, an additional external
overload protection is still advisable for either
alarm or manual reset.
Then it must be set below MCC value (at max
operating current):
• when the motor temperature is too high, then
the internal protector will trip
• when the current is too high the external
overload protection will trip before the internal
protection therefore oering possibility of
manual reset.
Compressor models SY 240 - 300 - 380 and
SM/SZ 185 P, X, Y versions are delivered with a
pre-installed motor protection module inside the
terminal box. This device provides for ecient
and reliable protection against overheating and
overloading (as well as phase loss/reversal.
The motor protector comprises a control module
and PTC sensors embedded in the motor
winding. The close contact between thermistors
and windings ensures a very low level of thermal
inertia.
The motor temperature is being constantly
measured by a PTC thermistor loop connected
on S1-S2.
Compressor models SM/SZ175 - 185 R & C
versions have been provided with a bimetallic
single-pole, single-throw thermostat located
in the motor windings. In the event of motor
overheating caused by low refrigerant ow or
improper motor rotation, the thermostat will
open. Because the thermostat is an automatic
reset device, it must be wired within a lockout
safety circuit with a manual reset to restart the
unit. For over-current and phase loss protection,
an external overload protector must be used.
The external overload protector can be either a
thermal overload relay or a circuit breaker:
A thermal overload relay should be set to trip
at not more than 140% of the compressor-rated
load current.
A circuit breaker, on the other hand, should be
set at not more than 125% of the compressor
rated load current.
The rated load current is the maximum current
expected during operations of the considered
application.
Further requirements for the external overload
protector are:
• Over-current protection: the protector must
trip within 2 minutes at 110% of the Maximum
Must-Trip current (MMT).
• Locked rotor protection: the protector must
trip within 10 seconds upon starting at a locked
rotor current (LRA).
• Single-phasing protection: the protector must
trip when one of the three phases fails.
Motor protection The table below shows the protection method for the various compressors models.
Recommended Required No test or additional safeties required
REQREC
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Overheating protection Over current protection Locked rotor protection Phase reversal protection
SM/SZ 115-125-160-175-185
R & C version
Internal thermostat External overload protection Reverse vent.
SM 112- 124-147 Internal motor protection Phase sequence detector
SM/SZ 084-090-100-110-120-148-
161 - SZ147
Internal motor protection Reverse vent.
SM/SZ 185 P, X, Y version Electronic module located in terminal box Reverse vent.
SY/SZ 240-300-380 Electronic module located in terminal box
REC
REQ
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Electrical data, connections and wiring