Fire & Smoke Actuator, 18 in-lb [2 Nm], Spring return, AC 120 V, On/Off, 2 x SPST
Fail-safe position

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Weight 1.9 lbs
Auxiliary Switch




Actuator Type

Spring return

Control type


maintenance free
18 in-lb
Torque motor
18 in-lb [2 Nm]
Power consumption in operation
2 W, 3.5 VA
Power consumption in rest position
1.5 W, 2.5 VA
Ambient humidity
5...95% r.H. non-condensing
Housing material
Electrical Connection
(2) 18 GA appliance cables with 1/2" conduit connectors, 3 ft [1 m],
Auxiliary switch
2 x SPST, 3A resistive (0.5A inductive) @ 250 VAC, one set at 10°, one set at 80°
Switching capacity auxiliary switch
3A resistive (0.5A inductive) @ 250 VAC
Auxiliary switch note
one set at 10°, one set at 80°
Angle of rotation
Noise level, motor
<45 dB (A) 
Position indication
visual indicator, 0° to 95° (0° is full spring return position)
Ambient temperature
32...122°F [0...50°C]
Non-operating temperature
-40...176°F [-40...80°C]
direction of rotation spring-return
reversible with cw/ccw mounting
Overload Protection
electronic throughout 0° to 95° rotation
Electrical Protection
actuators are double insulated
Quality Standard
ISO 9001
Degree of Protection
IP42, NEMA 2, UL Enclosure Type 2
direction of rotation motor
reversible with CW/CCW mounting
Data sheet type
CAD ThomasNetLink
Product Features
Torque 18 in-lb, 250°F for 30 min, for fire and smoke dampers
Nominal voltage
AC 120 V
Nominal voltage AC
120 V
Nominal voltage frequency
50/60 Hz
Power Supply
120 VAC, ±10%, 50/60 Hz
Power supply tolerance AC
Mechanical accessories
Electrical accessories
Family Series
FSTF Series
Shaft Diameter
1/4" to 1/2" round, centers on 1/2"
FSTF120SUS, FSTF120-SUS, FSTF120-S, FSTF120S, Belimo FSTF120-S US
Running time selection
50...79 sec
Running Time (Motor)
<75 sec @ 250°F [121°C]
Running time motor note
@ 250°F [121°C]
Running time (Fail-Safe)
<25 seconds
Running Time (Fail-Safe)
<25 sec @ 32...122°F [0...50°C]
Running time (Fail-Safe) note
@ 32...122°F [0...50°C]
Emergency control function
Spring Return
Noise Level (Fail-Safe)
<62 dB (A) 
Degree of protection IEC/EN
Degree of protection NEMA/UL
UL Enclosure Type 2
Not purchasable function
Tagging function
Auxiliary Switch
The type FSTF spring-return actuator is intended for the operation of smoke and combination fire and smoke dampers in ventilation and air-conditioning systems. The actuator will meet requirements of UL555 and UL555S when tested as an assembly with the damper. Square footage of damper operated will depend on make and model per damper manufacturer UL testing.
Mounting of the actuator to the damper axle shaft or jackshaft is via a cold-weld clamp. Teeth in the clamp and V-bolt dig into the metal of both solid and hollow shafts maintaining a perfect connection. The specially designed clamp will not crush hollow shafts. The bottom end of the actuator is held by an anti-rotation strap or by a stud provided by the damper manufacturer. The actuator is mounted in its fail safe position with the damper blade(s) typically closed. Upon applying power, the actuator drives the damper to the open position. The internal spring is tensioned at the same time. If the power supply is interrupted, the spring moves the damper back to its fail-safe position.
Typical Specification
All smoke and combination fire and smoke dampers shall be provided with Belimo FSTF, FSLF, FSNF, or FSAF actuators. All substitutions must be approved before submission of bid. Damper and actuator shall have UL 555S Listing for 250°F &/or 350°F. Actuator shall have been tested to UL 2043 per requirements of IMC 602.2 and NEC 300.22 (c). Where position indication is required -S models with auxiliary switches or damper blade switches will be provided per code requirements.
Agency Listing
cULus acc. to UL60730-1A/-2-14, CAN/CSA E60730-1:02, Listed to UL 2043 - suitable for use in air plenums per Section 300.22(C) of the NEC and Section 602 of the IMC. California State Fire Marshal Listing 3210-1593:104
Safety Notes
Screw a conduit fitting into the actuator’s bushing. Jacket the actuator’s input and output wiring with suitable flexible conduit. Properly terminate the conduit in a suitable junction box. Retrofit Safety Note Use of the FSTF for replacement of other makes of actuators is limited in damper area. The FSLF is preferred for direct coupled applications. The FSTF may be applied for linkage applications on dampers 1.5 sq.ft. and smaller at velocities under 2000 fpm.
CP65 Warning
⚠ WARNING: For Belimo Products sold in California, these Products do or may contain chemicals which are known to the State of California to cause cancer and or birth defects or other reproductive harms. For more information see www.p65warnings.ca.gov.

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