Standard Compliant and Functionally Safe Engineering Design with Mechanical Auxiliary Contacts

www.moeller.net Standard Compliant and Functionally Safe Engineering Design with Mechanical Auxiliary Contacts The complete range of Special Publication contactors, efficient motor- starters and controlled Dipl.-Ing. Wolfgang Esser drives for the motor circuit. New simple to install solutions based on clever communication. Contactors DIL Motor-protective circuit-breakers PKZ Motor-starters MSC Softstarters DS4 Drives Rapid Link 46157_VER2100-956.indd 1 07.08.2008 10:50:50 Uhr Dipl.-Ing. Wolfgang Esser Head of Industrial Switchgear Product Support Business Unit Motor Starters and Drives Moeller GmbH, Bonn Standard-compliant and functionally-safe engineering design with mechanical auxiliary contacts New, electronic-compatible auxiliary contact modules Information for quick readers DILA-XHIR11 for the contactor relay DIL A and for the most popular contactors DIL M7 to DIL M32, complement the xStart Even highly automated machines and systems cannot be product system [1]. The new auxiliary contacts provide an designed without electromechanical components which opportunity to discuss the topic of contact or control circuit feature electrical isolation, a high level of safety and excellent reliability. This technical publication additionally examines performance on the interfaces to the electronic inputs and different auxiliary contact constructions from the point of outputs. Contacts can occasionally cause contact faults due view of their suitability for usage in safety-related controls. to unfavourable circumstances and conditions. Contact faults must be avoided at all costs as a very high level of availability is In control circuits occasional malfunctions can occur even expected from machines and systems due to economic and with the use of top-quality switchgear. These difficulties can technical safety considerations. Moeller plays its part and be avoided by a problem-orientated engineering design provides improved auxiliary contacts, but the design engineer, approach. In this special publication potential sources of the installation specialist and the operators must also provide disturbance are highlighted and preventative solutions for support. The influencing variables are described in this engineering design are indicated. Well-known principles of publication as constructive measures, engineering principles reliability and safety with electrical low-voltage switchgear and ambient influences. systems are explained. This publication endeavours to make this topic understandable for all persons who do not have a background in electrical technology. Different parameters influence the in Table 1), which are available as ready the requirements placed on the contacts contact reliability made products on the market. The and have produced new terms which individual solutions include advantages have led to the confusion of many users. Four aspects influence the quality level and disadvantages. The most important New terms have always been associated of the contact or control circuit reliability disadvantage relates to limitations with with the escalation in the requirements of electromechanical switchgear and the relationship between different and with a more exact description of protective devices on the interface to types of contacts for safety circuits with the relationship and dependance the electronic systems, and in the regard to the reductions in electrical between different types of contacts. circuits with very low currents and load capability and the frequent voltages: limitation of application possibilities, or the absence of electrical isolation Contacts with electrical isolation for • Constructive features of the contact (will be explained later). safety functions element, • Current and voltage levels which are The term “auxiliary contact” sounds One of the most important features of to be switched, very simple at first. The demands placed contact-relevant switchgear continues • Engineering design principles with on it however are very comprehensive to be the electrical isolation provided interconnection of several contact and partly physically contradictory. by the contacts, which provides a high blocks Table 2 shows in very simplified form level of safety, e.g. for personnel safety, • and the ambient conditions. the typical demands placed on the and on which the entire safety contacts with different product groups philosophy is based. The electrical The contact reliability or contact security which feature different actuation isolation ensures that the isolated is not a constant factor, but deviates devices. The method of actuation conductors on the output side are truly from circuit to circuit within a certain heavily influences the construction of potential free. In contrast to switching tolerance. The tolerances can be the contact and the remedies to contact with semiconductors it must be noted influenced by the four factors reliability problems. that a leakage current will flow in the mentioned above. The competence of off state and that a dangerous touch a switchgear manufacturer is primarily Auxiliary contacts are frequently involved voltage may exist on the output. responsible for the first criterion. Over in the mastering of safety-related tasks, A second significant difference between the years there have been various e.g. personnel protection with mechanical contacts and semiconductor solutions for optimisation of the contact dangerous machines and systems. Hence contact elements is associated in the reliability of auxiliary contacts (examples various safety standards have dealt with transfer resistance and in the related 2 46157_VER2100-956.indd 2 07.08.2008 10:50:52 Uhr heat dissipation. The heat dissipation circuit-breakers). They are designed to Those who are not familiar with the is about 10 times higher on semi- switch different types of loads (motors, construction principles of switching and conductors than on an electromechanical heating systems, lighting, capacitors, protection devices initially assume that contact for the same current. This aspect etc.) with different rating data (power, the auxiliary contacts always assume plays a significant role with high-power current, voltage) over a suitable lifespan. the same switch position as the main contacts. The demands on the main contacts contacts. However, this obvious result from the corresponding product assumption is not always possible to standards, for example from the group realise on the timing front. For example, Contact types and standard-conform IEC/EN 60 947, but also from the the linear motions of the actuators of relationships between contacts construction and installation standards, the main and auxiliary contacts may such as IEC/EN 60 204-1 [2]. vary in length, so that acceleration path The risk assessment prescribed for and the slowdown path leads to differing machines and systems in compliance Auxiliary contacts are also referred to switching time points. The main and with the EU machine directive is usually as supplementary contacts or control auxiliary contacts are no longer switched performed by machine specialists. This contacts (Figure 1). They belong to the on and off using the same contact is why the most well-known and auxiliary or control devices (e.g. control mechanism, at the latest since the different types of contacts and their devices, contactor relays, relays). They switchgear has been developed, peculiarities should be explained here are also used for auxiliary functions on constructed and combined as a modular first for the electrical specialist personnel. the described circuit-breaker devices. system. Previously the contact paths of With the contact types it is initially They are mainly used to signal switching auxiliary and main contacts more or less important to differentiate between or malfunction states, for interlocking exhibited significant differences with main and auxiliary contacts for the sake circuits or logic and sequence controls the non-modifiable switchgear, because of the standards. Main contacts or with low to high loading. different voltages, currents and load high-power contacts belong to the types with varying arcing conditions circuit-breaker devices (e.g. contactors, had to be mastered, which inevitably Technological and economic aspects Important criteria for safety applications Construction features Positively driven Advantages Disadvantages Mirror contacts contacts Switch in a switch, introduces a certain Under certain Integrated enhancement of the circumstances, if N/O See right Probably no microswitch degree of protection, can and N/C contacts are be used for wide current available and voltage ranges Vibration sensitive, sensitive to interference, Attractively priced, Reed contacts low loadability, short- No No space-saving circuit protection difficult Expensive, voltage supply Wear free, insensitive dependent, outputs Electronic to soiling, insensitive frequently potential No No circuits to vibration relevant, difficult short- circuit protection Attractively priced, no New auxiliary For 2 contacts the space limitations in terms of Yes, for use in Yes, for use in contact DILA-XHIR11 of 4 “normal” contacts loadability with current safety circuits safety circuits from Moeller is required and voltage values Table 1: Different example solutions for auxiliary contacts with the main advantages and disadvantages. In safety applications positively driven contact blocks, or even mirror contacts are required 3 46157_VER2100-956.indd 3 07.08.2008 10:50:52 Uhr Demands on the auxiliary contact with

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