Emergency stop control components are a dime a dozen: small, large and round, rugged for harsh environments and design-oriented for a coherent machine image. No matter what you are looking for – reliability has to be the top priority. This is why you should not compromise on quality to save money. Of course, the same applies to all control and signaling devices, but especially to the emergency stop. Otherwise you could be in trouble if there’s an emergency. So when selecting the manufacturer, pay attention to experience and product quality. Respected brands, such as RAFI, will offer you a wide range of emergency stop actuators to choose from. Detailed technical data helps make the decision easier – in RAFI’s case you will find these in the eCatalog.
Now for the product itself: Most people have seen an emergency stop or emergency power off. And, even more likely, they no longer use the terms switch and button in everyday language. Virtually everybody just says emergency stop or emergency power off. Both are often used synonymously. We will clarify whether this is correct as we go on. However, what is absolutely certain is the actual switch type of the latch switch. The way the mechanism works is that the operator presses the switch to engage it. This closes a circuit and performs the desired action. Such switches are mandatory for plant and machinery - in accordance with the German industry standard EN ISO 13850, which we will discuss in more detail later on. Their purpose is to ensure the safety of employees in an industrial environment.... More
Emergency stop, emergency off, or emergency power off
As mentioned above, every machine needs at least one, if not more, emergency stop control components. The question is: does this also mean emergency power off actuators? To find out, we can look at the Machinery Directive 2006/42/EC, or more precisely Annex I, Section 184.108.40.206 “Emergency stop”. The text only refers to an emergency stop if the actuator is used to avert impending danger. So there must be a difference between emergency stop, emergency power off, and emergency off. And there is. Briefly: Emergency stop actuators stop the machine, emergency power off disconnects the power supply. What about emergency off actuators? Opinions differ here. There isn’t a clear definition in industry. In some cases, emergency off is used as a generic term for the other two types, and in some cases it is used synonymously for one of them. That is why we will leave this term out in further discussion so as not to create any confusion. Further details on the distinction are provided by various standards and the Machinery Directive already mentioned.
EN 13850 und EN 60204 – Stop categories
EN ISO 13850 is a harmonized standard concerning the safety of machines, in particular it provides emergency stop design guidelines for relevant machines. Apart from EN 60204, it is one of the most important guidelines when it comes to emergency actuators. The EN 13850 standard defines, among other things, the various stop categories.
Stop category 0
Actuation immediately disconnects the power supply to the actuator elements, so the actuator acts as a normally-closed contact for the circuit. Emergency power off falls under this category. In this case, the machine is not first returned to a safe state, but may continue to run mechanically for a while. Therefore, a potential danger still exists even after actuation.
Stop category 1
The actuator, in this case the machine emergency stop, first puts the machine or system into a safe and non-hazardous state. Only then is the energy supply to the drive elements disconnected. This category includes the emergency stop function.
Stop category 2
In a way, this is the reverse of category 0: The energy supply is maintained, but the machine is placed in a safe state. This type of stopping is not permitted for emergency stop actuators and is therefore not used.
In the annex Safety of machines of the standard EN 60204-1, we find under Electrical equipment of machines Part 1 further remarks on the difference between the actuators. The reaction after actuation of the switch is decisive. On the one hand, the emergency stop stops machine movements with potential danger in an emergency; on the other hand, the emergency power off cuts power from the entire system in an emergency. Machinery Directive 2006/42/EC adds here that emergency stop actuators must bring the hazardous process to a halt as quickly as possible while simultaneously triggering certain safety movements, if necessary. The question of whether to use emergency stop actuators or emergency power off switches for machine safety has a clear answer: The emergency stop is usually the safe choice.
Legending and color selection for emergency control components
In accordance with DIN EN ISO 13850 Safety of Machinery Emergency stop function — Principles for design, there are clear specifications on legending and colors used for emergency stop control components. They must be clearly recognizable, easily visible, and quickly localized, this is emphasized by the MRL 2006/42/EC. For this reason, the control element always has the safety color red, while the background is in the contrasting color yellow. Labels should be avoided because, according to the risk assessment, things have to happen quickly in an emergency and additional information could undermine or abort the reflex action, which can lead to hazards for people and machines.... Less
Emergency off sometimes covers emergency stop and emergency power off, so is not used due to the non-selective definition. The emergency power off switch interrupts the power supply of a machine or system to avert danger in emergencies. This means that the machine does not necessarily remain in position and may still pose a hazard. In contrast, an emergency stop first brings the machine into a safe state and then cuts off the power supply. So the emergency stop provides a higher level of safety and is used in most machines. However, one thing is the same for emergency stop and emergency power off: Actuation is by strong pressure, unlocking or resetting is by turning.