Standard Compliant and Functionally Safe Engineering Design with Mechanical Auxiliary Contacts

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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

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

46157_VER2100-956.indd 3 07.08.2008 10:50:52 Uhr Demands on the auxiliary contact with the product groups Construction features and influences which are to be controlled Contactor relay Timing relay Contactor Overload relay

DIL A ETR 4, DIL ET DIL M ZB

Actuation method Electromagnetic Electromagnetic Electromagnetic Thermodynamic

Mechanical/electrical lifespan Very high Very high Very high Low

Operating frequency Normal to medium Normal to high Low to normal Very low

Contact force Medium Low Medium to high Very low

2 changeover Contacts per unit 4, 6, 8 1 ... 8 2 contacts

Are part of Are part of Shock from Influences from the basic unit Shock the basic unit the basic unit the contactor

Mainly loading from Normal Normal Normal Normal the environment

Preferred location Control panel Control panel Control panel Control panel

led to the necessary contact clearances systems (e.g. zero-speed monitors, a differentiation is made between the (isolating gaps) and contact forces. The speed transducers) directly on the duration of the actuation of a contact differences in the switching paths, e.g. equipment. between permanent contacts and compensated using springs, with the pulse contacts, where switching can effect that auxiliary and main contacts In earlier days when only be processed differently. In terms of are actuated with more or less a large electromechanical contact elements the contact reliability and the effects time delay. were available, the small differences in of an uncertain contact in terms of the switching times or contact sequences this publication, it is still interesting A fundamental principle of the safety were purposely used and early make if the effect of a contact fault can be circuit is that the switching state of the or late break auxiliary contacts or eliminated by the repetition of a auxiliary contacts will close safely to the overlapping contacts were relevant switching command. A manually switching state of the main contacts. (Figure 2). These small differences with actuated control circuit device can Actually even more is desired. If an a very large spread are rarely used in usually be actuated again after a fault. auxiliary contact closes and an indicator the age of electronic circuitry and now Other switching commands occur on light switches on, one wants to assume electronic timing relays with definable an automated basis, or are process as a result that the corresponding motor and exact timing are used. dependent or dependent on a certain is now rotating. The amateur would position of a machine. In these cases the assume that if the indicator light does With early-make contacts and late-break contact can frequently not be made or not light, it can be safely assumed that a contacts the next differentiation with can only be made with a lot of effort. motor which they can probably not see the contact types has been mentioned. In particular, contact faults which only does not rotate. This conclusion is not It is a matter of the reaction to an occur infrequently are not desirable and valid and dangerous, because a series actuation function. There are are therefore very difficult to localise. of faults in the circuit are possible (e.g. N/O contacts, which are closed by cable breaks, defective lights, welded the mechanical or electromechanical For engineering the important principle main contacts, etc.), which can also lead actuation of a switching or protection is that the auxiliary N/C contact and the to the indicator not lighting up. With device. They are open in the quiescent auxiliary N/O contact of a device can not special safety-relevant factors it may state of the base unit in contrast to an close simultaneously (normal demand, be necessary to implement redundant N/C contact which is closed in the assured with positively operated control circuits1 or the equipment may quiescent state and which opens by contacts) – with the exception of the be monitored with additional protection actuation of the base unit. Ultimately special version “overlapping contacts”.

1 Redundancy = use of more than one device (system), to ensure that when a device (system) malfunctions another will assume its function. 4 Terms: full or partial redundancy, online redundancy, off-line redundancy

46157_VER2100-956.indd 4 07.08.2008 10:50:53 Uhr Table 4: Auxiliary contacts of different switching and protection devices are loaded in different manners by the basic units and the Motor-protective Control circuit main applications. The approximate ratings are Circuit-breakers Position switches circuit-breaker devices mainly true for the main applications of the devices. PKZ NZM RMQ 16 /22 AT

Stored energy Stored energy Manually actuated Machine actuated mechanism mechanism

High Medium Medium Very high

Low to normal Low Normal to high Low to very high

Low to normal Medium to high Low Medium

1... 6 2, 4, 6 1 ... 6 1, 2, 3

Heat of the Are part of Shock Shock indicator light the basic unit

Normal to high Normal Normal to high Normal to very high

Control panel, Small enclosure, Control panel On machine small enclosure on machine

Devices with auxiliary contacts Devices with power and auxiliary contacts

Figure 1: Example for switching and protection devices with main or power contacts or / and with auxiliary contacts

46157_VER2100-956.indd 5 07.08.2008 10:50:53 Uhr Furthermore, it also applies that an insurance association guideline ZH1/457 be closed simultaneously on the auxiliary N/C contact opens before the coined the term “positively driven same device. One critical aspect is auxiliary N/O contact closes (Figure 2). contacts”, which has been replaced the possible skewed alignment of the In principle, the engineering should in the standards in the meantime by contact bridge (Figure 3), if one of ensure that a switch-off command the term “positively driven contact the outer contacts welds. There were always has priority before a elements”. Even today after more than long discussions in the standardisation simultaneous switch-on command. 30 years, the meaning of this term is committees relating to whether the In order to ensure this, control circuit not comprehensively known among all required minimum clearance between devices for switch on and off are the specialists who are involved in the contacts should be measured or mutually electrically interlocked. machine safety technology field. verified by an impulse voltage test. The confusion has been compounded The current standard requires an by incorrect translations in other impulse voltage test on “artificially Functional safety of the contacts has languages and unforgivable mistakes welded” devices. economic and technical aspects by contradictory definitions in standards which have appeared later. A contactor relay can have several In addition to the easily comprehensible groups of positively driven contacts economic consequences of a reduction Positively driven contact elements, simultaneously as well as the mirror in the availability of a machine or system, to IEC/EN 60 947-5-1, Annex L [4]: contacts described later. Positive potential safety problems should be used, e.g. for self-monitoring in operation must be indicated in the avoided [3]. The employer’s liability machine control circuits. They make circuit diagram by a parallel double insurance association are primarily an exclusive statement concerning line which connects the filled out concerned with the personal safety the relationship between different circles on each symbol of the positively of the machine operators on power types of auxiliary contacts on one driven contacts. An example from the operated presses. A milestone was the and the same contactor relay standard is shown in Figure 4. so-called “Press safety controls”. With (devices where the actuation forces A manufacturer specification on the this important step in electrical safety are generated internally). It is device does not introduce any clarity technology of machines, the definition necessary over the entire lifespan as under certain circumstances a of the first term defining the relationship to exclude that the combination device can feature both positively between different contact types was of n auxiliary N/O contacts and m driven as well as non-positively driven undertaken. The employer’s liability auxiliary N/C contacts may never contacts, and therefore the specification of positive operation is preferably made in the manufacturers Switch position OFF catalogue only. ON Switchgear with external actuation (e.g. pushbuttons, position switches) can not feature positively driven contacts according to the standard

Switch direction because they do not feature a maximum actuating force. With a The contacts are closed (conducting) in the areas large actuating force it is possible to marked in black bend every contact and achieve that N/C and N/O contacts are closed simultaneously. With these types of Contact path in mm devices only control circuit isolator with positive operation to IEC/EN 60 947-5-1, Annex K [4] can result. This term signifies that a “welded contact” can only be broken apart by a sufficient force. This assumes that the Switch position ON Switch direction OFF force is transferred directly between Contact: 1 2 3 4 5 6 7 8 the actuation element and contact 1, 2, 3 Main contacts: N/O contact 4 Auxiliary contacts: N/O contact 6...8 and without elastic elements (typical: 5 N/C contact As the requirement for early- control circuit device Emergency- 6 Early-make contact, early-make N/O make and late-break are not Stop). 7 Late-break contact, late break N/C defined, generally an overlap is implemented 8 overlapping contacts The switchgear manufacturers contribute to the uncertainty with the users. Figure 2: Contact sequence diagram for representation of the relationship with the actuation of differing contacts of switchgear. In principle normal N/C contacts will open before normal Whereas the term positively driven N/O contacts close. Early-make contacts, late-break contacts and overlapping contacts are usually was used exclusively with contactor used today in special cases only. relays in the standards, there was

46157_VER2100-956.indd 6 07.08.2008 10:51:00 Uhr direction” due to the differing force ratios between main and auxiliary N/C contactÖffner → contacts. The solution which was finally agreed and used in the standard was ≥≥ 0,5 mm* 0.5 mm mirror contacts. This contact definition

N/OSchließer contact → for the first time made a statement concerning the relationship of the switch position on main and auxiliary contacts. Hereby it can only by a statement in one direction concerning the relationship of main circuit N/O contact to an auxiliary N/C contact.

→ Mirror contacts, to IEC/EN 60-947-4-1, Annex F [5]: ≥≥ 0.50,5 mm Öffner N/C contact The mirror contact is an N/C contact, → which can not be closed simultaneously with the main contact. The test is undertaken on artificially welded contactors. The open state of the mirror contact is N/OSchließer contact verified during an impulse voltage test or a contact clearance of at least

**im in the hier case gezeigten shown Fall, here, with a 0.5 mm must be measured. double-breakbei einer Doppelunterbrechung, the clearance can A contactor may feature several mirror bekann split die into Strecke 2 x 0.25geteilt mm. werden, in 2 x 0,25 mm. contacts. At the current time mirror contacts are known and standardised exclusively on contactors. “Mirror Figure 3: If for example the outer right make contact welds with a contactor, the contact bridge of the switched off contactor may skew. With “positively-driven contacts” it is demanded that the break contacts” should not be confused contact does not close in this case, but rather, that a clearance of 0.5 mm is retained between the with “positively driven” contacts. contacts for the entire lifespan of the contactor. Various safety circuits are based on the assumption Mirror contacts can be simultaneously that the break contact and make contact of a contactor can never close simultaneously. compliant with the requirements of “positively driven contacts” to IEC/EN 60 947-5-1. Mirror contacts must be clearly marked mention of “positively driven contacts” Positively driven contacts are useful for on the device or in the documentation with contactors in their advertising. This a safe switching of the logic functions of the manufacturer. If a symbol is was due to the fact that the contactor within safety-related circuits (safe used to identify the mirror contact it relay and small contactors (< 3 ... 4 kW) interrelationship of auxiliary contacts). must correspond with the are generally identical in construction However, they do not fulfil the representation in Figure 5. and differentiated primarily in the use previously described expectation of the A designation of the contact in the of the standard conform designation of user in terms of making a statement circuit diagram is not stated in the the terminals. The advertising had the concerning the switching state or a standard in this case as opposed to effect that the users referred incorrectly malfunction of the main contacts. Here the “positively driven contacts”. to the relationship between main circuit there were discussions for a long period N/O contacts and auxiliary N/C contacts of time concerning the definition A typical application for mirror as “positively driven contacts”. This may “incomplete positive operation” or a contacts is to provide a highly-reliable be the case on small contactors, on lar- “positively driven operation in a single monitoring for the (switching) state ger contacts the difference between the contact forces with main and auxiliary contacts is so large that the conditions for positive operation can no longer be assured. Here too unwanted deformation can occur during a malfunction. According to the standard the term “positively driven contact elements” makes no statement concerning the parity of the switch Figure 4: Left: Example of a standard compliant representation of positively driven N/O and position with main and auxiliary N/C contacts and a non positively driven N/C contact in a circuit diagram. Right: Example of a possible contacts, but rather refers exclusively marking on a device, for devices which also contain positively driven contacts. to the auxiliary contacts.

46157_VER2100-956.indd 7 07.08.2008 10:51:00 Uhr of the contactor in control circuits auxiliary N/C contact in the module device for world markets for use in of machines. However, the mirror also fulfils the demands of a mirror North America. It is also assigned with contacts should not be relied on as contact relative to the N/O main the CCC mark for use in China. The the only safety device. The standard contacts in the base unit. Base units combination of all these important recommends self-monitoring of the and auxiliary contact modules are safety features with a universal area mirror contact. The standard implies suitable as a result of these features for of application and at a “normal price” that the main contacts are use in safety-relevant controls with the can be found on very few of the N/O contacts which is not always the additional benefit that the contacts of “special auxiliary contact” solutions for case. Unfortunately it is evident that the auxiliary contact module have been enhanced contact reliability or electronic the terms “positively driven contacts” optimised for switching of small currents compatibility on the market. Most of and “mirror contacts” have been and voltages. They are also excellently these offers are pure “specialists” which edited to the disadvantage of the suited for example, to safely switch can be used for very few applications. user by different standardisation 1 mA at just 5 V (signal currents) on the committees. input of an electronic control under unfavourable ambient conditions. At Current and voltage level influence a contact loading with U = 17 V and the contact reliability The new auxiliary contact alternative I = 5.4 mA (control current) a failure rate DILA-XHIR11 rounds off the product l < 10-8 is the result. This specification The following applied until the range means that statistically only one introduction of electronic control 1 switching malfunction can be assumed systems at the start of the 60‘s: “A high The new auxiliary contact module DILA- after 100 million switching operations. control voltage, e.g. 230 V, generally XHIR1 provides 1 electronic-compatible results in a high control circuit reliability auxiliary N/O contact and 1 electronic- A very important feature of the new so that in contrast to low-voltages compatible auxiliary N/C contact with auxiliary contact with electrical isolation (e.g. 24 V) a control circuit reliability significantly enhanced contact reliability, is that it can be used for the “large” calculation was unnecessary”. This in the xStart system for a contactor relay currents and voltages of “normal” statement still continues to apply today or for contactors with frame sizes DIL M7 auxiliary contacts. For this reason a if the use of a high control voltage is to DILM 32. It features the well-known solution involving the internal parallel possible. Higher control voltages offer screw terminal technology known in the connection of auxiliary contact elements additional benefits, and at a higher system and the terminal designations for in separate contact chambers, with four voltage the required control currents contactor relays to DIN EN 50 005 independent contact points has been are lower and they result in a lower (N/C 61-62 and N/O 53-54). The contactor selected. This means that the same voltage drop and often require smaller relay base unit features 4 other “normal” contacts can also switch AC-15 currents cross-sections. The generation of an contacts and each contactor features 1 up to 6 A and operating voltages up to AC control voltage is frequently cheaper “normal” auxiliary contact in the base 500 VAC, or can switch DC voltages up than a DC voltage. However, the inputs unit. These “normal” contacts can be to 250 VDC and DC-13 currents up to and outputs on electronic systems for N/C or N/O contacts as required. 10 A. The thermal continuous current low voltage and current levels are

Ith = IAC-1 at an ambient temperature of cheaper to implement. As the control The particular highlight of the auxiliary 60 °C is 16 A. The contacts can even be circuit reliability in today‘s highly contact module DILA-XHIR11 is that its protected against welding with 10 A gL automated manufacturing and contacts are compliant in the base unit fuses. This wide field of application processing systems is very significant, to the described positive driven eliminates other well-known solutions the benefits of electromechanical and requirements regarding the contacts such as gold-plated contacts, as the electronic components – as with the to one another and to the auxiliary gold is no longer present after just a auxiliary contact modules DILA-XHIR11 contacts. If the module is combined few switching operations. Parallel – have converged from a technological with the mentioned contactors, the connection of contacts in separate point of view. At a failure rate of l < 10-8 contact chambers makes simultaneous a calculation of the contact reliability occurrence of even minute levels of and failure probability is superfluous for impurities at several contact points most applications which operate today much more improbable. The contact using the very popular 24 V control reliability is increased by a factor of voltage. 500 ... 2000. Even the “safe isolation” feature to DIN EN 61140 [6] with Figure 5: If mirror contacts are identified with reinforced insulation which is demanded a symbol, the symbol shown must be used. In the in the chemical industry, is fulfilled with standard a clear identification of the mirror “normal” auxiliary contact modules up contacts by the manufacturer on the device to a rated insulation voltage of 690 V. and / or in the documentation is demanded. Of course the new auxiliary contact Identification in the circuit diagrams is not mentioned in contrast to the “positively driven DILA-XHIR11, with the same price level contacts”. as “normal” auxiliary contact modules is approved by the UL and CSA as a

46157_VER2100-956.indd 8 07.08.2008 10:51:00 Uhr Technical usage of different contact with a small electronic circuit which voltage recovery. This can lead to types in circuits ensures the self-maintenance function). tripping of current-dependent trip- This is called three-wire control with release mechanisms due to the inrush Impulse and 2-wire control require self-maintenance. If an interruption in current peaks which could eventually different handling methods in a circuit. the voltage occurs on these circuits, lead to the next fault. There are cases, such as inching duty for the drive will remain stationary, the example, where the motor should only self-maintenance is interrupted and Machines and their controls have run as long as a pushbutton is manually the drive will not restart after voltage become more complex with the increase actuated (e.g. control of shutters and recovery. This behaviour is required for in automation. Automation has lead to louvres). This is the simplest method most machines in order to eliminate the an increase in the incidence of two-wire of actuation. With the louvre control dangers posed by an automatic restart control, which is not always in the form mentioned, a reversing circuit is required (with automatic reset). of a latching switch. In many cases in order to move the louvres in the spring-return switches operate like opposite direction. With these types of It is possible to operate with 2-wire two-wire control, e.g. position switches circuits, opposing commands for “open” control (latching switch) only on systems which are actuated by cams or discs. and “close” are mechanically or where an automatic restart does not With two-wire control one is posed with electrically interlocked to avoid short- present a danger after a voltage recovery. the task of preventing an automatic circuits. This type of equipment includes for restart of machines and systems. This example compressors, pumps, heating is implemented by routing the control In cases in which the motor should or lighting (the danger should be clarified voltage via a contactor relay with a pulse continue to run independently of the on a case by case basis). Even in cases control circuit and self maintenance duration of actuation, e.g. until an end where there are no safety considerations behind the control voltage transformer. position is reached, a contactor has to when operating with two-wire control, If the voltage drops out the entire be maintained (for louvre controls with it is important to note that many loads control is interrupted at this central low powers, operation is undertaken may switch on simultaneously after a point, an automatic restart is prevented

Correct Incorrect

Earth fault Effects with earth fault before and after switch on Before After Before After Before After Without effect F blows Without effect Contactor can Coil on 230 V, F blows. Coil no longer be usually no pickup, remains on 230 V, a switched off by danger of de- can no longer be “off” pushbutton struction switched off by “off” pushbutton F blows Contactor F blows b switches on without command

F blows The same however c generally without damage

Figure 6: The position of the individual switchgear device influences safe operation. Examination of correct and incorrect positioning with clarification of the consequences of a fault scenario

46157_VER2100-956.indd 9 07.08.2008 10:51:00 Uhr and undefined switching states for the Improvement of the contact reliability pressure equalisation which is dependent entire control system are avoided. of relay outputs particularly on the current and voltage Examples of circuits are contained in the levels involved. A certain amount of Moeller wiring manual and the Moeller Included are limit value encoders with circulation is required for temperature safety manual. low-power relay outputs, such as equalisation. Most switching and thermostats, pressure switches, various protection devices are usually IP20 regulators, etc. integrated into the devices when considered from the Position of the equipment and circuits. Here there is a danger that front end, with the terminals requiring number of contacts in a control circuit the relay outputs may chatter due to significantly large apertures in order to a poorly set hysteresis value and exhibit connect the required conductors. The general sequence of the equipment a very high operating frequency. Both Labyrinths are used on the construction in modern control circuits is not random, malfunctions unnecessarily reduce the design side to prevent the ingress of dirt but rather is intended to offer the life of downstream contactors and and to simultaneously guarantee the greatest possible safety during a other equipment. In order to avoid required air-gap and creepage distances. malfunction. It is assured that the circuit these types of faults we recommend IP20 means however, that practically all cannot be interrupted and that a circuit the use of off-delayed timing relays, e.g. devices must be enclosed, e.g. installed can be shut-down by an earth fault. ETR 4, with short time ranges in order to in a control panel or in an insulated Figure 6 shows and explains the correct introduce a little time-lag into the circuit. enclosure. This is also undisputed. design and clarifies the problems of At the same time timing relays act like a incorrect design. In principle the contact protection relay for the regulator Regardless of these facts a lot of dirt contactor coil should always be due to their low power consumption. It can sometimes be found in the devices connected to the neutral pole or a is possible to use a thermistor machine when contact reliability problems are comparable conductor after a control overload relay instead of a timing relay analysed. It is frequently underestimated transformer or power supply. where the regulator contact is connected how much dirt gets into the interior of to the terminals for the sensor cable the device during the commissioning Unfortunately today you can still see instead of the thermistor sensor. with open control panels. The installation many circuit diagrams where too many phase is also critical if the intended floor contacts are connected in series. This is covering has not been fitted to the hall a serious engineering design fault in Consideration of ambient influences or access to the hall, or when a lot of many respects, as the voltage drop can on the contact reliability drilling takes place on the open control be very large due to this chain which can panel. Some electricians try to remedy mean that there is not enough pickup Switching and protection devices can the dirt in the control panel by blowing voltage available for a contactor to be not be manufactured so that they are it out with pressurised air. Unfortunately switched on. This is particularly perfectly sealed, as the switching small particles of dirt are then blown problematic if the cables between the processes require a certain amount of into the switching and protection individual contacts also exit the control panel, and for example, are used in emergency-stop circuits which are hundreds of meters long. The author has seen circuit diagrams with 40 contacts connected in series. How should a faulty contact be localised? If many contacts are necessary for example, 6 contacts should be placed on a contactor relay and one contact of this contactor relay should be should be connected in series with a further small number of contacts. Thus a relatively clear number of contacts are connected to the full control voltage. The number of contacts used can be larger with a higher control voltage than with a low voltage, but the ambient conditions must also be considered. It can be opportune in critical cases to connect contacts in parallel and then to connect the contact pairs in series.

Figure 7: The safety relay ESR 4-.. in a 22.5 mm wide enclosure is available from Moeller as a processing alternative for standardised safety circuits. Space is saved in comparison to the parallel connection of several contactor relays and the wiring and testing expense is reduced.

46157_VER2100-956.indd 10 07.08.2008 10:51:01 Uhr devices. Almost all switchgear have a Summary: Literature: minute quantity of oil which attracts and binds fine dust particles. The mix Moeller provides the new auxiliary [1] Wolfgang Esser, hardens to form a non-conductive layer contact module DILA-XHIR11 with “Then new motor starter which leads to contact problems. A high enhanced contact reliability. generation xStart, again with level of cleanliness is required during The electronic-compatible modules application orientated installation and commissioning. Many enhance the fail-safety of systems where highlights!“,VER 2100-937GB, control panels are ventilated using a large amount of dust is expected to be Moeller GmbH, Bonn, 2004 external fans. Where does the air from a factor and where only small currents Download: the fans come from? In America the in conjunction with a low voltage are http://www.moeller.net/binary/ installation is undertaken with conduits to be switched. The modules excel ver_techpapers/ver937en.pdf which are flanged directly to the control simultaneously by a high level of panel and which attract the dirt from loadability which enables universal use. [2] DIN EN 60 204-1, 1998-11-00 far away due to the draught which is Highlights are the provision of “Safety of machinery ; Electrical created. “positively driven contacts” and “mirror equipment of machines, Part 1: contacts” for standard compliant use in General requirements“ safety-relevant controls. The contacts Safety relays for standard with electrical isolation can be protected [3] Wolfgang Esser, safety-relevant tasks by gL fuses up to 10 A without having “Mirror contacts for highly- them weld due to a short-circuit. This reliable information relating to In the area of safety technology on document provides some impulses for safety-related control functions“, machines and systems there are engineering design and commissioning VER 2100-944GB standard tasks which have often been taking the subject of contact reliability Moeller GmbH, Bonn, 2004 solved in the past by the interconnection into account in order to enhance the Download: of several contactor relays and even by availability of machines and systems http://www.moeller.net/binary/ using timing relays. Moeller provides a together with the switchgear ver_techpapers/ver944en.pdf series of safety relays with the manufacturers. designation ESR 4-… (Figure 7) as a [4] DIN EN 60 947-5-1 processing alternative for these tasks. *VDE 0660-200, 2005-02-00 These relays with a width of 22.5 mm “Low-voltage switchgear and featuring a BG certification (German controlgear – Part 5-1: Control employers liability insurance) and circuit devices and switching GS mark (German safety tested) and elements; electromechanical require less space in the control panel control circuit devices“ and the wiring and test expense requirement is reduced. [5] DIN EN 60 947-4-1 *VDE 0660-102, 2006-04-00 “Low-voltage switchgear and controlgear – Part 4-1: Contactors and motor-starters; Electromechanical contactors and motor-starters”

[6] DIN EN 61 140 *VDE 0140 Part 1, August 2003 “Protection against electric shock – Common aspects for installation and equipment”

46157_VER2100-956.indd 11 07.08.2008 10:51:04 Uhr Moeller addresses worldwide: www.moeller.net/address

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