Danfoss Performer SM Series, Selection & Application Manuallines

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Motor protection
compressor model
overheating
protection
overcurrent
protection
locked rotor
protection
single-phasing
protection
SM / SZ 084 - 090 - 100 - 110 - 120 - 148 - 161 Internal Internal Internal Internal
SM / SZ 115 - 125 - 160 - 175 - 185 Internal Compulsory external overload protector
SY / SZ 240 - 300 - 380 Internal Internal Internal Internal
compressor models sM / sZ 084
- 090 - 100 - 110 - 120 - 148 - 161
have internal motor protection to
protect 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
the data sheets. The protector is
located in the star point of the motor
and, if activated will cut out all three
phases. It resets automatically. While
not compulsory, additional external
overload protection is advisable for
either alarm or manual reset.
compressor models sM / sZ 115 -
125 - 160 - 175 - 185
have a bimetallic
single-pole, single-throw thermostat
located in the motor windings. This
thermostat will open In the event of
motor overheating caused by low
refrigerant flow or by incorrect motor
rotation. Because the thermostat is
an automatic reset device, it must be
wired in a lockout safety circuit with
a manual reset to restart the unit. For
overcurrent and phase loss protection,
an external overload protector must
be used for the SM / SZ 115, 125, 160,
175 and 185 models. The table below
shows the protection method for the
various compressor models.
compressor models sY / sZ 240 -
300 - 380
are delivered with a factory-
installed motor protection module in
the terminal box. This device provides
efficient, reliable protection against
overheating, overloading, and phase
loss or reversal. Connected to the
module are 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
constantly measured by the (PTC)
thermistor loop connected on S1-S2
(refer to the electronic protection
module wiring on page 13).
If any thermistor exceeds its response
temperature, its resistance increases
above the trip level (4,500 Ω) and
the output relay opens the contacts
M1-M2. After cooling below the
response temperature (resistance
< 2,750 Ω), a 5 minute time delay is
activated. After this delay, the relay
closes the contacts M1-M2. The time
delay may be cancelled by interrupting
main power (L-N disconnect) for
approx. 5 seconds. The monitoring
fuction, however, is inactive for 20
seconds after shutdown.
sYsteM design RecoMMendations
external motor protection
All safety devices must comply with
the local safety requirements. 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's 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 operation in the
application; it can be found either in
the corresponding data sheets or in
the of Danfoss RS+3
TM Compressor and
Condensing Unit Selection Software,
available from the Danfoss web site.
The tripping current must never
exceed the MMT (Maximum Must-Trip)
internal motor protection