Air brake contactor 3TF usually refers to a Siemens 3TF series power/contactors model, commonly used in control panels for air compressor and air brake systems, not a brake component itself. It is an electrical contactor used to switch the motor or solenoid load of an air brake/air compressor circuit, typically in industrial or rail/vehicle applications.
The “3TF” series from Siemens refers to a line of AC contactors.
A contactor is essentially a heavy-duty, remote-control switch: it makes (closes) or breaks (opens) an electrical circuit under high current, often for motors or other heavy AC loads.
“Air-break” / “AC contactor” means the switching happens in open air (not in oil or vacuum), using contacts that physically separate to open the circuit when de-energized. The arc (if any) is quenched via an arc-chute/arc-chamber.
These contactors allow remote control (via a coil) of heavy AC circuits: e.g. for starting/stopping motors, switching large loads, or combining with overload / protection relays to build motor starters. “3TF” is Siemens’ series designation for three pole AC contactors used for motor and power switching in control circuits.
Typical Applications
- Motor control / motor starting: Use with AC motors — starting, stopping, reversing, switching on/off, often along with thermal overload relays for protection.
- Controlling large AC loads beyond what small switches or relays can handle: lighting banks, heaters, capacitors, transformers, industrial loads.
- Industrial automation & control panels — remote control of power circuits, safety circuits and switching operations in factories, machines, HVAC systems, etc.
Because they are “air-break” and designed to handle high currents and voltages, 3TF contactors are widely used in industrial environments.
Other typical applications
- Interlocking and safety: Used with auxiliary contacts for electrical interlocks (e.g., forward–reverse, star–delta, pump changeover) and to cut power under abnormal conditions via overload relays or safety circuits.
- Switching capacitors or heaters: Can be used to switch capacitor banks (with proper rating) or large heater banks in industrial process control.
- Motor starting and stopping: Used in DOL or star–delta starters to switch three‑phase motors (pumps, compressors, fans, conveyors, etc.) on and off safely from a control circuit (push buttons, PLC, or relay logic).
- Control of air‑compressor / air‑brake systems: Commonly used to control the motor of an air compressor or the solenoid/valve power circuits in industrial air‑brake or pneumatic systems inside MCC and control panels.
- Remote and automatic control: Allows PLC or control relays to operate large loads remotely with a small control signal, providing electrical isolation between control and power circuits.
Main Usage of a 3TF Series Siemens Air-Break Contactor
- Motor Control (Most Common Use)
- Used to Start and Stop 3-phase induction motors.
- Works with thermal overload relays to form a motor starter.
- Suitable for AC-3 duty (motor starting, full-load switching).
Examples:
- Water pumps
- Compressors
- HVAC motors
- Industrial machinery motors
- Remote Switching of Heavy Loads
The contactor allows you to switch large loads remotely using a small control signal.
Used for:
- Heaters
- Large lighting banks
- Transformers
- Capacitor banks
- Solenoids
- Automation & Control Panels
3TF contactors are commonly used in:
- Industrial automation systems
- PLC-based control panels
- Motor control centers (MCC)
- Distribution and power factor correction panels
They help automate switching sequences, safety interlocks, and motor operations.
- Reversing / Star-Delta Starters
Different contactor combinations (two or three contactors) form:
- Forward–Reverse starters
- Star–Delta starters
3TF series is widely used in these motor starter circuits.
- Safety Interlocking
Used to create:
- Electrical interlocks
- Mechanical interlocks
to prevent two circuits or motors from turning on simultaneously (e.g., forward & reverse motors).
A 3TF Siemens contactor is used to:
✔ Control and switch AC motors
✔ Remotely operate heavy electrical loads
✔ Protect circuits (with overload relay)
✔ Build automation and interlocked control systems
✔ Form starters (FFF, F–R, Star–Delta)
A Siemens 3TF contactors works as an electromagnetic switch that opens and closes power to a three phase load (like a motor) using a small control signal.
Basic working principle
- Inside the contactor there is a coil and an iron core with moving contacts mounted on a movable armature.
- When the control voltage is applied to the coil, it creates a magnetic field that pulls the armature towards the core, causing the main contacts to close and connect the three phase supply to the load.
- When the control voltage is removed, the magnetic field disappears, a return spring pushes the armature back, and the main contacts open, disconnecting the load from the supply.
Control and protection role
- The coil is driven by push buttons, relays, or a PLC, so a low power control circuit can safely switch a higher power motor circuit on and off.
- Auxiliary contacts on the 3TF34 (NO/NC) provide feedback and interlocking (e.g., for forward/reverse or star/delta logic), and the contactor is usually combined with an overload relay so if over current occurs, the control to the coil is cut and the contactor drops out, protecting the motor.
Typical features
- Three main power contacts (for three‑phase supply) plus auxiliary NO/NC contacts for signaling, interlocks, and protection circuits.
- Coil voltage can be various (e.g., 230 V AC, 415 V AC, 110 V AC, 24 V DC, etc.), so the exact variant must be checked on the nameplate or catalogue before replacement.
- Used inside MCCs and control panels to start/stop motors, control solenoid valves, or cut off power in fault conditions for air‑brake or air‑compressor systems.
Typical Specifications and Range (for 3TF)
Here’s a breakdown of what the 3TF series covers (varies by specific model):
Parameter / Range: Typical Values / Range
Frequency (AC): 50/60 Hz
Rated Insulation Voltage: Up to 690 – 1000 V
Rated Operational Voltage (Power Circuit): Up to ~380 V (for AC-3 utilization)
Rated Operational Current (depending on model): From ~9 A up to several hundreds of A (e.g. 9 A-400 A, sometimes even more) across the series
Poles Typically 3-pole (for 3-phase circuits)
Auxiliary Contacts (optional): Some models allow additional auxiliary contact blocks (NO/NC) for control circuits or signaling.
Standards / Certification: Conform to international standards like IEC/IS (e.g. IEC 60947-4-1 / IEC947)
Typical Uses: Switching / controlling AC motors (squirrel-cage or slip-ring), solenoids, capacitors, lighting loads, heaters, transformers, etc.
For instance: a contactor such as “3TF3200” is a 3-phase contactor with AC-3 rating of 16 A; coil voltage 110 V AC @ 50 Hz; suitable for motor load up to ~7.5 kW (≈ 11 HP) in 3-phase.
How to identify exact specification:
To get exact ratings, you need the full code from the device or datasheet (for example: 3TF34 **xx‑**xx), which defines:
- Rated operational current (Ie) and power (kW) at different voltages
- Coil voltage and frequency
- Contact configuration of auxiliaries (e.g., 1NO+1NC, 2NO+2NC)
Without the complete code, treat “3TF34” as the series/size and refer to the Siemens 3TF contactor catalogue or panel drawings to select a matching replacement.
