Fire and Smoke Documentation

Frequently Asked Questions

What is the difference between a control and a Fire & Smoke actuator?

Fire and Smoke actuators are essentially the same as regular control actuators. They tolerate 250°F or 350°F for a half hour and must operate in under 75 seconds to open or to close per UL555S or in 15 seconds for replacement in regions where UBC times are required. Las Vegas requires 60 seconds or less, so the 15 second actuators are used there. The one exception is the FSAF24-BAL which springs in 20 sec and drives open in 60 seconds worst case since the potentiometer’s lowest setting is 20% (80% of 75 sec = 60 sec).


Can linkages be used with the FS series actuators?

The data sheets for each actuator indicate that:

  • FSLF is direct coupled only.
  • FSNF and FSAF can use the full range of linkages and housings.
back to top


Can the Belimo FS actuators be used in Generator applications where the 15 second opening time is critical?

Yes, however there are some cautions. The FS actuators are NEMA 1 rated. The actuator must be shielded from rain entrainment and the ambient temperature must be within its rating (FSLF and FSNF +32°F, FSAF -22°F).

What is then recommended for generators which must start in 10 seconds?

Since a generator damper is spring open, the AF actuator with a 20 second full load spring time can be used. A parallel blade damper with a 50% authority will have about 80% flow minimum at 10 seconds. This is enough to ensure the damper opens the rest of the way and the generator will not be starved for air.

What is recommended for 2 second start generators?

A parallel blade damper establishes air flow faster than an OB. The FSNF with a 15 second spring time must be used with a linkage geometry that speeds up the damper rotation. Each application is different and field adjustment of the linkage should be expected. Approximately 2 seconds of actuator rotation must achieve enough opening of the damper to avoid velocity pressure torque overload and stalling. Spring torque is highest when the actuator is full open. It may be necessary to drive the actuator open and then mount in the closed position. This maximizes the spring force to open quickly. Increasing the number of actuators may be necessary since the linkage geometry causes a loss of torque.

What is recommended for actuation on the discharge of a generator where exhaust temperatures hit about 170°F?

All Belimo actuators have a storage temperature of 176°F. Since the actuator is powered to keep the damper closed when the temperature is at ambient, there is no problem. When the generator is tested, the damper springs open unpowered. The 176°F temperature limit is in effect. If the ambient then exceeds the actuator limits for a little while, life span may be shortened, but not seriously. If the temperature is expected to exceed 176°F for over a half hour, the actuator should be mounted outside the discharge.

back to top

Mechanical and Electrical Paralleling

Can all FS actuators be mechanically paralleled?

FSAF actuators can be mechanically paralleled. All standard linkages can be used.

FSLF actuators are not recommended to be mechanically paralleled. There are no linkages are manufactured by Belimo. Ruskin makes one for a special application. Use one FSNF instead of two FSLF would be preferred in any event.

FSNF actuators are not recommended to be mechanically paralleled using the ZG-102. The UL555S test is 20,000 full open-closed cycles. In a limited test the mechanically paralleled application with a ZG-102 and double the torque load, it was found that there is a one in eight chance of failure before 20,000 full cycles due to excessive gear stress. If the damper is going to be cycled frequently, failure is more likely. It is recommended that one actuator be placed at each end of a jackshaft; this reduces gear stress.

Can the FS actuators be electrically paralleled?

Yes, all can be wired to operate in unison.

back to top

Noise Level

What is the noise level of the Belimo FS actuators?

The holding level is inaudible. It does not register on a meter, so it is not rated. The spring is audible, which only runs once a day to once a year.

back to top


What is the quality features does Belimo Fire and Smoke products offer compared to the competition?

Compared to the competition Belimo Fire and Smoke products offer:

  • 5-year warranty on entire Fire and Smoke actuator product line
  • Current draw for the size and torque of damper is the lowest
  • Product size is the smallest making space constraints less of a problem
  • Belimo actuators do not have the type of problems competition has had. Actuators always spring closed when required. Electronics are long lived and failures virtually unknown. Gears never “fret” causing actuators to stick open. No “creep closed” problems occur by not driving back open when short power interruptions occur. Vibration noise is never a problem.
  • Track record is clear – Belimo actuators live longer than competition.
  • ISO 9001 quality control – average failure rate is certified below .3% over the entire warranty period.

Do I need to specify “Belimo” to receive it from the damper manufacturer?

Yes. Some manufacturers provide Belimo as the standard offering or as default in certain applications, while others use competitors’ actuators.

back to top

Replacement for Competitive Failures

What are the most important code issues for replacement?

All codes require life safety systems to be in working order and defects to be corrected. Interpretations on the details vary within different jurisdictions. UL has specifically stated that they do not regulate replacements and that the local inspectors are the final authority. The codes themselves do not detail replacement rules, so the Authority Having Jurisdiction (AHJ, usually the Fire Marshal or Building Official) interpret the codes and inspectors vary in interpretations. NFPA 80 regulates fire dampers. NFPA 105 regulates smoke dampers. They both require repairs be initiated as soon as possible and that a record of corrections be kept on premises.

While they do not regulate the replacement of old actuators, UL does state that they expect repairs be done in accordance with the manufacturer’s field servicing policy. Belimo provides replacement installation instructions for this purpose.

Always use an actuator that is UL555 and UL555S listed with the damper manufacturer. One or more of the Belimo actuators is UL555(S) listed with each.

In general, inspectors want an “equal or better actuator”. Some jurisdictions require a permit and inspection when a large number of replacements are needed or when changing model or function of actuator. This varies. In most jurisdictions, actuator replacement is considered an “ordinary repair”.

If any fire alarm wiring is touched or if any structural modifications made, a permit and inspection may be required. Retest of the alarm functions should be expected.

Retesting of the damper is expected and sometimes witnessed. The Belimo instructions include a testing checklist.

Belimo has New York City MEA approval and tags are shipped with actuators going into that area.

Belimo has California State Fire Marshal Listing on the FSLF and FSNF and the FSAF has been submitted.

What are the most important technical issues to look at for replacement?

  • Equal or better actuators should be used.

TTT-VAT is a mnemonic device that can be used:

  • Time: Actuator should operate as fast or faster than the old motor. The exception is that the UBC 15 second time is no longer in effect. The UL 75 second time is now code. Consult with AHJ if going to slower time.
  • Temperature: The FSLF and FSNF are rated at 350°F. The FSAF is for 250°F. Codes in the US are 250°F. 350°F is used in some engineered smoke control systems, but is not a code issue.
  • Torque: Replacement must be equal or greater. Requirement varies by damper manufacturer depending on their UL555(S) testing. For replacement in general:
    • 4 sq. ft. or less = FSLF at 350°F.
    • Up to 12 sq. ft. per FSNF at 350°F.
    • Up to 12 sq. ft per FSAF at 250°F.

While the actuators may be capable of more damper area, without a test to prove it, the UL tested torque should be used. Both the FSNF and FSAF have been tested for large multi-section assemblies also. Details available.

Actuators listed above can operate a greater area than stated, however some old dampers are corroded and dirt has gummed up parts. Some shifting of ducts may have occurred and the torque requirement may be higher than originally passed by UL. The actuator output is higher and the damper requirement lower at ambient than at elevated temperature. The operation at elevated temperatures is the important factor. Spare torque should be provided.

  • Voltage: Must be the same. In the US 90% are 120V, 10% are 24V. Only the FSAF can take DC power.
  • Amperage: Must be equal or lower than the original. Belimo is lowest and can replace all competitors of the same torque without fear of overloading a breaker.
  • Test: Damper should be operated 3 times open to close to ensure proper operation. The damper and actuator must be tested after replacement. Just like a gas valve replacement, the contractor takes responsibility.

In most cases, drive open, open the sensor or remove power to ensure that the actuator springs the damper closed. Then drive open again, check sensor (use a heat gun) and controls operation as described in Conformance Testing.

back to top

–S Model

Do the -S version of the F&S actuators meet code requirements for damper position monitoring?

Yes with three provisos.

  1. They must be UL555S listed with the damper manufacturer. Any field mounting requires an exception from the AHJ.
  2. The wiring must be supervised per fire alarm codes – typically chapter 9 of IBC.
  3. They cannot be used to signal alarms, just to indicate open-close monitoring. They are not UL864 listed.

Some AHJ’s do not accept the actuator switches as proof. Others do not like the blade switches and prefer the actuator switch. Most codes do not say "HOW" to monitor, only that it must be done under certain circumstances. Proximity switches are another option.

Given the cold-weld clamp of the Belimo and the robust connection between the jackshaft and the damper blade, the Belimo aux switches are technically equal to blade switches with the coat-hanger connection which is not as strong.

The smoke detector has two sets of contacts. Upon detection of smoke, one set opens to cut power to the actuator and spring the damper closed. The other set closes and tells the fire alarm panel that a damper has closed.

In 2010 California approved use of actuator auxiliary switches for proof of operation connection to the Fire Fighters Smoke Control System panel.

back to top


How do I specify Belimo?

The Belimo specification is on the Belimo website F&S Dashboard. Customer service can also send to a customer.

back to top


Can the Belimo FS actuators be used in higher than normal operating temperatures?

No, the ambient rating for long life is the same as other actuators. The 250°F or 350°F test temperature is for a ½ hour in the UL555S test.

Can the FSNF be used at temperatures below 32°F?

Yes and No. The technical submittal states correct specifications and should be observed. The FSNF has been tested at low temperatures and loses some torque and speed when it is operated. It will work, but not at specified torque, speed, or number of cycles.

back to top


Can the FS actuators be mounted to valves?

No. The thermal isolation, faster motor and different electronics have not been tested for the condensation or frequent opening and closing of valve service.

back to top

Breaker Sizing

How many Belimo FS actuators can be placed on a single transformer or breaker?

It is unlikely that actuators would be the only load since smoke detectors and other life safety may be on the same breaker. It is wise to leave spare power available. Always use the run draw. See local codes for allowable loading.

The equation is VA = Volts X Amps.

Wire runs must be large enough gauge or short enough that there is no voltage rop on way to actuators.

The 120 VAC draws 18 VA according to data sheet.

Using VA = volts X amps, 18 = 120 X amps, or the FSLF120 draws 18/120 = .15A.
Then given a 20A breaker and an allowable load of 75% = 15A, 15A / .15A = 100.
100 actuators could be placed on a 20A breaker.

FSNF: From the data sheet, both draw 27VA or the 120V amp draw is .23A. A 20A breaker loaded to 15A can carry 15 / .23 = 65 actuators.

FSAF: From the data sheet, the 24V is 10VA and the 120V draw is .1A. So 3 actuators can go onto a 40VA transformer and 150 actuators can go onto a 20A breaker.

From the data sheet, the 24V is 10VA and the 120V draw is .1A. So 3 actuators can go onto a 40VA transformer and 150 actuators can go onto a 20A breaker.

What? How can these numbers be true given the higher draws competitors show?

Yes, the numbers above are true. At 120V on a 20A breaker:

  • FSLF is 100
  • FSNF is 65
  • FSAF is 150

Why are there some differences between 24V and 120V among the actuators above?

The transformer losses vary and are optimized for different voltages. The FSAF is a slower actuator and thus draws a lot less due to gear ratio.

Are FS actuators designed for continuous duty?

FS actuators are not designed for continuous duty at elevated temperatures. However, the FSAF24-SR proportional actuator can be proportioned using a 2-10V signal (or 4-20mA with a 500Ω resistor. In this way, it functions the same as an AF24-SR or AF24-MFT except it is a 75 second actuator.

The 2-position FS actuators are designed for fire and smoke UL555S applications. The UL testing is for 20,000 cycles. At elevated temperatures, they are tested for 3 cycles at a high torque load. The FSAF24-SR is UL tested for 100,000 10 degree movements and 20,000 full open-close cycles. The elevated temperature is for ½ hour and for 3 cycles.

back to top