The Belimo EFB24-SR-S is a high-torque spring-return (fail-safe) damper actuator delivering 270 in-lb [30 Nm] of torque with modulating 2-10 VDC control on AC/DC 24 V power. It direct-couples to round or square damper shafts up to 1.05 in. with a universal clamp and is a member of the EFB platform for large commercial HVAC dampers that must fail to a safe position. On power loss the internal spring drives the damper to its fail-safe position in under 20 seconds. Two built-in SPDT auxiliary switches signal damper position or interlock equipment.
Specifications sourced from the official Belimo EFB24-SR-S technical data sheet (rev 2026-03-09).
Overview
Belimo EF-Series actuators are high-torque spring-return drives for large commercial HVAC control dampers requiring fail-safe operation. The EFB24-SR-S produces 270 in-lb [30 Nm] and mounts directly to round or square damper shafts up to 1.05 in. with its universal clamp (a crank arm and brackets are available for jackshaft and linkage applications). The fail-safe direction is reversible by CW/CCW mounting, and a 5 mm hex crank allows manual positioning. The spring returns the damper to its fail-safe position in under 20 seconds when power is removed. A 2-10 VDC signal (or 4-20 mA with the ZG-R01 resistor) modulates the damper, with 2-10 VDC position feedback; the spring provides fail-safe return.
Best for
- Modulating large-damper control with fail-safe return
- High-torque damper and louver control (270 in-lb)
- Outdoor-air, mixing-box and economizer dampers that must fail safe
- End-position signaling or equipment interlock (2x SPDT)
Key Features
Spring-Return Fail-Safe
A mechanical spring drives the damper to a safe position on power or signal loss (under 20 seconds), with no external power required to fail safe.
270 in-lb High Torque
Sized for large commercial dampers; direct-couples to round or square damper shafts up to 1.05 in. with a universal clamp.
Modulating 2-10 VDC
Accepts a 2-10 VDC (or 4-20 mA with ZG-R01) signal with 2-10 VDC position feedback.
Reversible Fail-Safe Direction
The spring-return (fail-safe) direction is selectable clockwise or counterclockwise simply by mounting orientation.
Manual Override Crank
A supplied 5 mm hex crank (3/16" Allen) lets you position the damper by hand for setup or service.
Two SPDT Aux Switches
Two built-in SPDT auxiliary switches (1 mA-3 A) signal damper end position or interlock other equipment.
Technical Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Belimo |
| Part Number | EFB24-SR-S |
| Actuator Type | Spring-Return (Fail-Safe) Damper Actuator |
| Nominal Voltage | AC/DC 24 V |
| Nominal Frequency | 50/60 Hz |
| Power Consumption (Running) | 8 W |
| Transformer Sizing | 14 VA |
| Torque (Motor & Spring) | 270 in-lb [30 Nm] (minimum, full rotation) |
| Control Signal | Modulating |
| Operating Range (Y) | 2-10 VDC (4-20 mA with ZG-R01 resistor) |
| Position Feedback (U) | 2-10 VDC (max. 1 mA) |
| Shaft Range | Up to 1.05 in. [26.7 mm] via universal clamp; crank arm available |
| Angle of Rotation | 95° (adjustable mechanical stops) |
| Running Time (Motor) | 95 s / 90° |
| Spring Return Time | < 20 s (< 60 s below -4°F) for fail-safe |
| Behavior on Power Loss | Spring returns damper to fail-safe position |
| Fail-Safe Direction | Reversible (CW/CCW) by mounting orientation |
| Auxiliary Switch | 2x SPDT, 1 mA-3 A (0.5 A inductive), DC 5 V-AC 250 V |
| Manual Override | 5 mm hex crank (3/16" Allen), supplied |
| Electrical Connection | 18 AWG plenum cable, 3 ft [1 m], 1/2" NPT conduit connector |
| Overload Protection | Electronic, full 0-95° rotation |
| Electrical Protection | Double insulated (Class 2) |
| Enclosure Rating | NEMA 2 / UL Type 2 |
| Ambient Temperature | -22 to 122°F [-30 to 50°C] |
| Agency Listing | cULus (UL60730-1A/-2-14, CAN/CSA) |
| Quality Standard | ISO 9001 |
| Plenum Rated | UL 2043 (suitable for air plenums) |
| Weight | 11 lb [5.2 kg] |
| Warranty | 5 Years |
Documentation
Related Products
Accessories & Mounting
Common Belimo accessories for mounting, linkage, signaling and powering the EFB24-SR-S, drawn from the actuator datasheet. All are stocked by ZOT Supply as an authorized Belimo distributor.
Mounting & Linkage
Electrical Add-Ons
Frequently Asked Questions
What is the Belimo EFB24-SR-S?
The Belimo EFB24-SR-S is a high-torque spring-return (fail-safe) damper actuator for large commercial HVAC dampers. It produces 270 in-lb [30 Nm] of torque, uses modulating 2-10 VDC control on AC/DC 24 V power, and on power loss its spring drives the damper to a fail-safe position. Its housing is rated NEMA 2.
Is the EFB24-SR-S a spring-return (fail-safe) actuator?
Yes. The EFB24-SR-S is spring-return: a mechanical spring drives the damper to its fail-safe position when power or the control signal is lost — no external power is needed to fail safe.
What happens to the EFB24-SR-S on power loss?
Its internal spring returns the damper to the fail-safe position in < 20 s (< 60 s below -4°F). The fail-safe direction (CW or CCW) is set by the mounting orientation.
How much torque does the EFB24-SR-S provide?
It delivers 270 in-lb [30 Nm] of minimum running and spring-return torque, sizing it for large commercial dampers.
What shaft sizes does the EFB24-SR-S fit?
It direct-couples to round or square damper shafts up to 1.05 in. using its universal clamp. For jackshafts or off-shaft mounting, a crank arm (KH-EFB) and brackets (ZG-120, ZG-JSA-3) are available.
What control signal does the EFB24-SR-S use?
It uses modulating 2-10 VDC control. The 2-10 VDC input also accepts 4-20 mA with the ZG-R01 resistor and provides 2-10 VDC feedback.
Does the EFB24-SR-S have auxiliary switches?
Yes. It has two built-in SPDT auxiliary switches (rated 1 mA to 3 A) for end-position signaling or interlocking other equipment.
How do you manually position the EFB24-SR-S?
Use the supplied 5 mm hex crank (3/16" Allen) to wind the actuator by hand for setup or service.
Is the Belimo EFB24-SR-S available from an authorized Belimo distributor?
Yes. ZOT Supply is an authorized Belimo distributor and carries the EFB24-SR-S. Every unit ships factory new with Belimo's full 5-year warranty and application support.
- Actuator Type:
- Fail-Safe
- Torque:
- 270 in-lb
- Control Signal:
- Modulating
- Voltage:
- 24 VAC/DC
- Auxiliary Switch:
- 2x SPDT
- Enclosure:
- NEMA 2
- Series:
- EF
- Feedback Signal:
- 2-10 VDC
