Technical Article

In Safe Hands

Moeller’s comprehensive range of safety components keeps people safe and machines turning

Safety in the workplace is of paramount importance. Today the onus is very firmly on machine builders and operators to provide totally effective measures that will prevent any harm coming to people, the processes and systems they work on, and the environment they work in.

Effective safety solutions require high quality safety components and the comprehensive range put together by Moeller Electric is quite simply, second to none.

Moeller's versatile range of protective components includes electronic safety relays, command and signalling devices, foot and palm switches, rotary switches and switch-disconnectors, safety position switches and signal towers – all complying with the latest international standards and in many cases going well beyond their requirements.

The most common safety products are traditional, hard-wired devices, such as emergency-stop push-buttons. According to the latest standards disconnection has to be initiated by a positive opening safety function, which means the forced opening of a normally closed contact.

Devices for stopping in an emergency must be accessible and functionally fit at all times. Moeller offers a big choice of reliable emergency-stop actuators, which are additionally tamper-proof in accordance with EN 418 by means of a positive non-tease action. Every time a stop signal is generated, its location will simultaneously be indicated. Thus, users can easily and quickly find and correct faults thereby minimising expensive downtime.

Rated to IP67/69K protection, three types of emergency-stop pushbutton are available in Moeller's new RMQ Titan range. These are pull-to-release with or without illumination, and key-operated. In the illuminated version an integral LED is permanently lit or lights up when actuated, according to requirements. This safety component is therefore easily visible even in darkened rooms, and saves having to fit a separate indicator light. All three can be fitted with a protective collar which is aimed at those applications where the emergency-stop needs to be protected against accidental actuation.

Some applications demand extremely speedy reaction in an emergency. Here, the FAK foot and palm switches with their large switching surface are an ideal solution. These devices allow users both safe and easy triggering by foot and by hand, even when work gloves are worn. Rated to IP67/69K they are made to meet the demands of even the most rigorous environments, including cleaning with high-pressure or steam-jet devices.

Often space is limited and very compact modules are required. For these situations Moeller has developed the Q25PV emergency-stop actuator, part of the RMQ16 series of command and signalling devices. The Q25LPV illuminated version is equipped with a multiple LED to give clear visual indication of a trip.

In a production environment people generally have to be separated from hazardous areas by the use of protective doors and protective hinged covers. These mobile protective mechanisms have to be monitored, so that in the case of an attempt to open a protected door or cover during on-going operation the safety components reliably switch power off. Moeller's range of position switches provide users with matching devices for every scenario.

Sliding doors, mobile or hinged protective mechanisms can be controlled with Moeller's safety position switches, the LS-ZB and LS4-ZB. Mounting is very easy thanks to the fact that the operating head of the switch allows flexible adaptation to the requirements of the installation site.

The opening of safety guards must initiate an immediate stop of the machine to remove any danger. If this is not possible, for example, because of machine tracking times, the doors or covers have to be kept closed until conditions are safe. Therefore an increased protection level with separate indication of door position is required. LS-ZBZ safety position switches featuring a holding power of up to 2,000N have been designed specifically for these tasks. Users have the choice of a magnet-powered version or a spring-powered model additionally providing reliable interlock even if the power fails. In order to open the protective guard in an emergency an auxiliary release mechanism is included.

Where swift reaction with minimal mounting space is needed, the LSR/TS hinge operated and the LSR/TKG hasp operated safety switches are ideal. Monitoring hinged doors and trap doors they instantly disconnect the power when the door is just slightly opened, even at an angle of 5°.

Within a safety control scheme, emergency-stop circuits as well as protective-door closures or safety mats and two-hand controls have to be supervised by electronic safety relays. ESR electronic safety relays from Moeller monitor the wiring in the control system and the de-energisation of the contactors in the power section. Relays with an actuating voltage of 24V are only 22.5mm wide, while the 230V modules measure just 45mm.

Used as safety relays for emergency-stop applications, the units switch several release current paths either for instantaneous (EN 60204-1 stop category 0) or for time-delayed (stop category 1) interruption of the power supply, once the emergency-stop button is actuated. If control cables are damaged in a way, which may cause short circuits to exposed conductive parts or to earth, the electronic safety relays react accordingly. Thanks to their ability to distinguish different sorts of failures, the relays switch off immediately, or they prevent reconnection until the fault is rectified. Dual-channel versions allow short-circuit and cross monitoring to be implemented.

Safety relays suitable for category 4 use feature an additional restart button monitoring function to prevent tampering. This function ensures that the enable signal is only given after the restart button has been released.

If the ESR is used to monitor safety guards, an automatic start function replacing the reset monitoring feature gives users the opportunity to reduce cycle times within the production area while keeping a high safety level.

Often two position switches indicate the status of one door. In these instances Moeller offers an ESR unit with simultaneity check. This relay is able to recognise a fault, if both position switches don't close within 0.5s of one another. As a result no enable signal for continued production is given.

Contact mats provide effective protection for people entering hazardous zones and can easily be monitored by ESR safety relays. As soon as a person treads on the mat, it generates a short circuit between two conductors, which disconnects the machine or process from the power supply.

As is the case of safety mats, Moeller has special safety relays designed for two-hand controls. Two-hand circuits require simultaneous operation by both hands to initiate and maintain the operating status of a machine. As a result the operator is protected, because he can not reach the danger zone during hazardous procedures. The electronic safety relay monitors whether or not both buttons are operated within 0.5s of one another.

Safety switches isolate electrical installations from the supply system to allow personnel safe access for maintenance or repair work and to prevent dangerous restarts. Reliable isolation, clear switching position and lockable off position are the most important points. Moeller's main switches are designed to provide the very highest levels of protection. The isolating gap is visible and restarting impossible. Panic switches, for example, can be locked in the off position using up to three padlocks simultaneously.

Signal towers complement Moeller's safety component range. In line with the saying “the sooner you see the signal, the quicker you can react” they are mounted on top of machines to give clear visual and audible indication of the operating status of machines and automated process sequences. Operators can see at a glance any stoppages, interruption in material flow or alarms as they occur. Consequently any problems or faults can be detected and resolved quickly.

This page last updated: 23 October 2007