Electrical data, connections and wiring
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 flow 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 offering 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 efficient
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.
If any thermistor exceeds its response
temperature, its resistance increases above the
trip level (4,500 Ω) and the output relay then trips
-ie. contacts M1-M2 are open. After cooling to
below the response temperature (resistance <
2,750 Ω), a 5 minute time delay is activated. After
this delay has elapsed, the relay is once again
pulled in ie. contacts M1-M2 are closed. The time
delay may be cancelled by means of resetting the
mains (L-N disconnect) for approximately 5 sec.
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 flow 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
REQ
REC
Overheating protection
Over current protection
Locked rotor protection
Phase reversal protection
SM/SZ 175-185 R & C version
Internal thermostat
External overload protection
Reverse vent.
SM112-124- SM/SZ147
Internal motor protection
Phase sequence detector
SM/SZ
084-090-100-110-120-148-161
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
22
FRCC.PC.003.B4.02
Application Guidelines