Electromechanical Safety Switch Overview

1 Industrial Safety Products 179 StandardsIEC 60947-1 explains the general rules relating to Low voltageswitchgear and controlgear. The purpose of this standard is toharmonize as much as possible the product performance andtest requirements for equipment where the rated voltage doesnot exceed 1000 Vac or 1500 60947-5-1 is part 5 of the general rules which relates toControl-circuit devices and switching elements where ratedvoltage does not exceed 1000 Vac or 600 Vdc. Also within thispart there is a section which considers Special RequirementsFor Control Switches With Positive Opening Operation. Anycontrol Switch which has this positive opening operation andconforms to these special requirements will be marked on theoutside of the product with this symbol: Positive Opening OperationAll the switches presented in this catalog feature positive open-ing contacts on the Normally Closed Circuits (see Notes).

2 These circuits are identified in this literature by the positiveopening symbol shown above. Positive opening ensures thatshould the NC contacts weld, they can be forced apart by nor-mal operation of the Switch , depressing the plunger, remov-ing the key, rotating the lever or pulling on the cable. In otherwords, an open circuit is guaranteed even after an electrical faultcondition has occurred. Although it should be usual practice toprotect the NC Safety circuit with a fuse of an appropriate ratingfor the control current being used, if this additional security isshorted out or bypassed, the positive opening feature ensuresthat the contacts will positive opening feature is specified within EN 60947-5-1chapter 3 sometimes referred to as EN 60947-5-1-3.

3 The stan-dard gives general requirements for the electrical current, volt-age rating and life characteristics of Low Voltage(120 to 1000 V) Switchgear. What distinguishes SafetySwitches from standard switches is their ability to meet the re-quirements of chapter 3, which describes the requirements forpositive opening operation. There are two main elements topositive opening operation;1. There should be no flexible members within the drive trainoperating the positive operating contacts this means thatwobble or flexible actuators cannot be The basic Switch shall incorporate a mechanism which willguarantee positive opening of the NC circuit. Both the Snap Ac-tion and Slow Acting basics used on our Safety range incorpo-rate this design feature.

4 The tests performed to confirm that thepositive opening mechanism complies with the requirements ofchapter 3 include:a) Passing 1000 A, at 110% of the rated voltage, throughthe contacts. This current flows until a protective fuse, inseries with the contacts, is blown. The Switch is operatedusing the minimum force and travel published in our in-stallation sheet. These first two steps are repeated the contact separation is confirmed using a 2,5 kVdielectric ) Verifying the contact robustness by applying a 10 Nforce to the moving contact and ensuring any distortiondoes not affect the Switch s dielectric ) Operating the Switch at the maximum specified current,in the maximum specified ambient temperature and con-firming the Switch s dielectric properties are not when these tests have been successfully concluded can aswitch claim positive opening.

5 To ensure complete impartialityof the performance we claim, Honeywell had these tests carriedout by an independent third party test : Normally Open (NO) contacts rely on spring mechanisms toopen the circuit. If a weld occurs on these contacts there isno guarantee the contacts will separate. Due to this limitationthese contacts are normally used for monitoring purposesand shall not form part of the Safety circuit. Normally Closed (NC) contacts are those which make circuitwhen either:-The Switch is not actuated neither depressed norrotatedor-The Key is inserted the guard is closedor-The Cable is up to tension but not pulled or cut The installation sheet provided with each product states theminimum required operating force and travel to ensurepositive opening.

6 It is essential that the mechanismemployed to operate the Switch can generate both theminimum and maximum required force and travel, and theextra travel needed to rotate the mechanism is available, butlimited so as not to damage the information on design requirements of positiveopening Switchgear and the Low Voltage Directive can befound in IEC 60947-5-1/EN 60947-5-1, EN 1088 and EN Machinery Directive 98/37/EC also gives further Safety Switches180 Industrial Safety Products Proper application ofelectromechanical switchesFor Electromechanical switches with pushrod actuators, the actuating force should be applied asnearly as possible in line with the pushrod or dog arrangements should be such that the actuator is not suddenly released to snap mechanisms for Electromechanical switches should be so designed that, under anyoperating or emergency conditions, the Electromechanical Switch is not operated beyond itsovertravel Electromechanical position.

7 An Electromechanical Switch should not be used as a me-chanical Electromechanical switches with lever actuators, the actuating force should be applied asnearly perpendicular to the lever as practical and perpendicular to the shaft axis about which thelever Contact Element Form defines the configuration of the con-tacts and the number of contacts within the Switch :Form Za - both contact elements have the Zb - the two contact elements are electrically Utilization Category defines the type of current carried (ac)Alternating current, (dc) direct current and the typical applica-tion in which the Switch is used:Ac15 - Control of Electromagnetic Loads(less than 72 VA)Dc13 - Control of contact rating Designation relates to the utilization cat-egories and defines the conventional thermal current Ith (A),rated operational current Ie (A) at rated operational voltages Ueand the VA rating:A600 - The A denotes the maximum VA rating (ac) andthe 600 denotes the maximum rated (ac) - The Q denotes the maximum VA rating (dc)and the 300 denotes the maximum rated (dc) IEC standards have been adopted by CENELEC (The Euro-pean Committee for Electrotechnical Standardization) and havebeen identified by replacing IEC with EN 60.

8 IEC 60947-5-1 then becomes EN 60947-5-1 CENELEC has defined the dimensions and characteristics oftwo types of limit Switch in the standards EN 50041 andEN standards relate to Low voltage switchgear andcontrolgear for industrial use and define the enclosure dimen-sions, the operating point for various head actuators, the earthterminal requirement, the terminal marking, and the minimumdegree of IP RatingWRONGWRONGRIGHTFIXED STOPRIGHTWRONGWRONGRIGHTRIGHT over-ridingcamover-ridingcamWRONGWRONGRI GHTRIGHT free positionSTOPend ofovertraveloperatedpositionend ofovertravelWRONGRIGHTnon-over-ridingnon -over-ridingElectromechanical Safety SwitchesIEC 60947-5-1/EN 60947-5-1 Designation & UtilizationRated operational current le (A)

9 VACategoryat rated operational voltage Uerating120 V240 V380 V480 V500 V600 VMakeBreakAc15A600631,91,51,41, ,60,3---- 43272125 V250 VDc13Q3000,550,276969Dc13R3000,220,12828 Industrial Safety Products 181 First DigitProtection against ingress of solid objectsIPTEST0no protection1protected against solid objects with a diameter greater than 50 mm2protected against solid objects with a diameter greater than 12 mm3protected against solid objects with a diameter greater than mm4protected against solid objects with a diameter greater than 1 mm5protected against dust-limited ingress (no harmful deposit)6totally protected against dustSecond DigitProtection against ingress of waterIPTEST0no protection1protected against vertically falling drops of water2protected against vertically falling drops of water when the enclo-sure is tilted at an angle up to 15 degrees3protected against water sprayed at an angle of 60 degrees from thevertical4protected against splashing water from all directions - limited in-gress (no harmful effects)

10 5protected against low pressure jets of water from all directions -limited ingress permitted6protected against powerful jets of water from all directions - limitedingress permitted7protected against the effects of temporary immersion in water8protected against the effects of continuous immersion in waterIP1stDigit2ndDigit3rdDigit4thDigitD egree of protectionIP ClassificationThe IEC 60529 standard describes a system for classifying thedegree of protection provided by the enclosures of level of protection given by the enclosure is indicated by theIP code system uses the letters IP (International Protection)followed by up to four digits normally only the first two digitsare first digit is numerical and indicates the level of protectionwithin the enclosure against the ingress of solid foreign objectsand access to hazardous parts by second digit is also numerical and indicates the level of pro-tection against the ingress of WATER into the third digit is a letter and indicates a higher level of protectionfor persons against access to hazardous fourth digit is also a letter and is used in exceptional casesfor supplementary the first or second digit is not required to be specified, then itis replaced by the letter X ( XX if both digits are not required).