Conveyor belt systems are used across a wide range of industrial sectors for transporting, positioning, and processing products. Along these systems there are moving parts that can pose a risk to persons in the vicinity. In many cases, it is necessary for operators, maintenance technicians, or cleaning personnel to be able to move along the conveyor while the installation is in operation. As a result, the use of physical guarding, such as fencing, is not always possible or desirable.
When physical guarding is absent or only limitedly possible, the risk must be reduced through additional safety measures. One of the most commonly applied solutions is the use of an emergency stop device that is accessible along the entire length of the hazardous zone. Pull-rope safety switches are specifically developed to fulfil this function and are widely used along conveyor belts, packaging lines, and comparable installations.
A pull-rope safety switch is a mechanically actuated safety switch that is activated by pulling a tensioned cable. This cable runs parallel to the hazardous zone, for example along a conveyor belt. As soon as the rope is pulled, or when it breaks, the safety switch changes the state of its contacts and an emergency stop is activated. This results in the safe stopping of the drive or process that causes the hazard.
The mechanical nature of this operation is of great importance. The emergency stop function does not depend on software, sensors, or an external power supply. This aligns with the requirements of the relevant safety standards (EN ISO 13850 / IEC 60947-5-5), which state that emergency stop devices must operate reliably and directly, even in the event of an electrical fault.
After activation, the pull-rope safety switch mechanically latches. The installation cannot be restarted as long as the switch remains in the latched state. Restoring the emergency stop function requires a deliberate manual reset, usually performed by turning a reset knob on the switch.
This reset only restores the emergency stop function and does not automatically lead to a restart of the machine. A separate start command is always required. This prevents the machine from unexpectedly starting after an emergency stop has been cleared.
The Safeline 4 (SL4) pull-rope safety switch from Mechan Controls is available in two versions:
SL4 pull-rope safety switches are available with a diecast aluminium housing. This version is suitable for general industrial applications where there are no increased requirements regarding corrosion resistance or hygiene. The housing provides sufficient mechanical strength for use in production environments with vibration and mechanical loads.
This version is widely used in logistics systems, assembly lines, and internal transport systems where the environmental conditions are relatively stable.
For applications in environments with increased exposure to moisture, cleaning processes, or corrosive influences, a version with a stainless steel housing is available. This material offers higher resistance to corrosion and mechanical degradation than aluminium and is suitable for applications such as the food industry or outdoor installations. The choice of stainless steel is particularly relevant when the switch is exposed to moisture for prolonged periods or when cleaning is a fixed part of the process.
| Feature | Specification |
| Maximum cable length | 75 metres |
| Reset method | Manual rotary knob, mechanically latched |
| Contact configurations | 3NC + 1NO or 2NC + 2NO |
| Housing | Diecast or 316 stainless stee |
| Standards | EN ISO 13850 / IEC 60947-5-5 |
| Additional option | Push button with mushroom head (E-stop) |
| Connection | Cable tension window on both side |
Pull-rope safety switches are designed for use over longer distances. Depending on the type, a single switch can monitor cable tension over a length of up to 75 metres. For longer conveyor belts, multiple switches can be used, with each section being safeguarded separately.
Correct adjustment of the cable tension is an essential aspect of the reliable operation of a pull-rope safety switch. The tension must be set such that the rope can be operated with limited force from any point along the installation, while preventing unintended activation. Too low a tension can result in pulling the rope not leading to immediate activation of the emergency stop, whereas too high a tension can lead to false activation or increased mechanical stress on the switching mechanism and mounting points.
In practice, the correct tension is achieved by using tensioning kits at the ends of the rope. These allow for controlled and reproducible adjustment during installation and commissioning. Many pull-rope safety switches are equipped with visual tension indicators, allowing it to be determined at a glance whether the cable is within the permissible tension range. This not only simplifies installation but also supports periodic inspections during maintenance.
The pull-rope switches from Mechan Controls are available with various combinations of normally closed and normally open contacts, such as 3NC and 1NO or 2NC and 2NO contacts. The normally closed contacts are used for the safety function, so that a cable break or activation automatically results in a safe state.
The normally open contacts can be used for signalling or diagnostics within the control system.
In addition to activation via the pull rope, the switch can optionally be equipped with an integrated emergency stop push button with a mushroom head. This allows a local emergency stop to be activated without using the rope. This function is often applied at the start and end points of conveyor belts or at operator stations.
When installing pull-rope safety switches, it is important that the rope is easily accessible along the entire length of the hazardous zone. The rope must be installed at an ergonomic height and must not be obstructed by structural components, guards, or cable trays.
To achieve uniform cable tension, tensioning kits are applied at the ends. Intermediate supports and guide eyes can be used to guide the cable around bends or obstacles without affecting the operation of the switch.
During commissioning, it must be verified that the switch responds correctly to pulling the rope and to cable breakage. In addition, it must be confirmed that reset is only possible after a deliberate action and that the machine does not restart automatically.
Although pull-rope safety switches are low-maintenance, periodic inspection is necessary. This includes checking that the cable is undamaged, the tension is correctly set, and the mechanism can move freely.
In practice, pull-rope safety switches offer a number of functional advantages that directly contribute to the reliability and applicability of the emergency stop device in industrial installations. An important aspect is the use of positively driven contacts. Because the switch contacts are mechanically forced to open or close, the safety state is directly linked to the physical position of the switching mechanism. This reduces the likelihood of hidden faults and increases mechanical reliability, particularly in applications where the switch is frequently actuated or exposed to mechanical loads.
Another practical advantage is that the emergency stop function is independent of an external power supply. Activation of the emergency stop is achieved exclusively through mechanical movement of the pull rope and the internal switching mechanism. As a result, the emergency stop function remains available even in the event of power failure or control system faults. This aligns with the principle that an emergency stop device must be able to function under all circumstances.
The physical design of pull-rope safety switches also contributes to clear and unambiguous operation. Both activation and reset of the switch provide direct mechanical feedback to the user. Pulling the rope or pressing an optional emergency stop push button results in a clearly perceptible and visible response. The manual reset requires a deliberate action, making it clear to the user that the emergency stop has been activated and has not yet been released.
In addition, pull-rope safety switches are designed to operate reliably under a wide range of industrial conditions. The mechanical construction is resistant to vibration, shock, and temperature influences commonly encountered in many production environments. This makes them suitable for use along conveyor belt systems and other installations where dynamic loads and environmental influences play a role.
A major functional advantage of pull-rope systems is the continuous accessibility of the emergency stop function along the entire length of an installation. Because the pull rope is installed parallel to the hazardous zone, the emergency stop can be actuated from any point along the cable. This is particularly important for long conveyor belts, where the use of individual emergency stop push buttons would result in large distances between operating points.
By making the cable continuously accessible, the requirement that an emergency stop must be quickly and directly reachable for persons located in or near the hazardous zone is fulfilled. This increases the practical effectiveness of the emergency stop device, especially in situations where an operator is not at a fixed operating position but moves along the installation during operation, inspection, or maintenance.
Pull-rope safety switches provide a functional and standards-compliant means of implementing a continuous emergency stop device along conveyor belt systems and other long installations where physical guarding is not practical. Through their mechanical operation, positive actuation, and clear reset functionality, they make a reliable contribution to machine and installation safety. Correct material selection, careful installation, and integration into the safety system are essential for safe and durable application.
€408,00
€442,00
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