Iec 62135 1 2015

I E C 62 5-1 ® Edition 2.0 201 5-05 I N TE RN ATI ON AL S TAN D ARD colour i n sid e Re s i s tan ce wel d i n g eq u i pm e n t – IEC 621 35-1 :201 5-05(en) P art : Safety req u i rem en ts for d es i g n , m an u factu re an d i n s tal l ati on T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing more than 30 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary More than 60 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C 62 5-1 ® Edition 2.0 201 5-05 I N TE RN ATI ON AL S TAN D ARD colour i n sid e Res i s tan ce wel d i n g eq u i pm en t – P art : Safety req u i rem en ts for d e s i g n , m an u factu re an d i n s tal l ati on INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 25.1 60 ISBN 978-2-8322-2664-3 Warn i n g ! M ake su re th a t you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission –2– I EC 621 35-1 : 201 © I EC 201 CONTENTS FOREWORD Scope Norm ative references Terms and definitions Environm ental conditions 1 Tests 1 Test condition 1 Measuring instrum ents 1 Type tests Routine tests Protection against electric shock General I nsulation General 2 Clearances Creepage distances I nsulation resistance 6 Dielectric strength 6 Welding circuit touch current Liquid cooling Protection against electric shock in norm al service (direct contact) General Rated no-load voltage at the output 3 Protection provided by barriers or the enclosure 20 Capacitors 21 Automatic discharge of input capacitors 21 6 Protective conductor current under norm al condition 22 Touch current in norm al condition 22 Protection against electric shock in case of a fault condition (indirect contact) 22 General 22 Protective provisions for welding circuit 24 I nternal conductors and connections 36 4 Touch current in fault condition 36 DC resistance welding equipment operating at mains frequency 37 6 DC resistance welding equipment operating at medium frequency 37 Continuity of the protective bonding circuit 37 Additional user requirements 38 6 Suppl y voltage 38 Conductors of the welding circuit 38 Thermal requirements 38 Heating test 38 Test conditions 38 Tolerances of the test parameters 39 Beginning of the heating test 40 Duration of the test 40 I EC 621 35-1 : 201 © I EC 201 –3– Temperature m easurement 40 Measurements conditions 40 2 Surface temperature sensor 40 Resistance 40 Embedded temperature sensor 41 Determ ination of the ambient tem perature ( ta ) 41 Determ ination of cooling liquid temperature ( ta ) 41 7 Recording of tem peratures 41 Lim its of tem perature rise 42 Windings 42 External surfaces 42 3 Other components 44 Protection from thermal hazards in norm al service (direct contact) 44 General 44 I dentification of hot surfaces 44 Protection provided by insulation or other barriers 45 4 Protection provided by supplemental cooling 45 Abnormal operation 45 General requirem ents 45 Stalled fan test 45 Cooling system failure 45 Overload test 46 Provisions against mechanical hazards 46 General 46 Risk anal ysis 46 General 46 2 Read y-to-use equipment as in delivery state 46 Equipm ent not read y to use as in delivery state 46 Equipm ent not read y for use and designed to be incorporated in m ore com plex equipm ent 47 Measures 47 Minim um measures 47 Additional measures 47 Conformity of com ponents 48 Starting for m anual operated equipment 48 I nstructions and markings 49 1 I nstructions 49 Markings 49 Marking of terminals 49 Annex A (informative) N ominal voltages of suppl y networks 51 Annex B (normative) Construction of suppl y circuit terminals 52 B Size of terminals 52 B Spacings between suppl y circuit term inals 52 B Connections at the terminals 53 B Construction of the terminals 53 B Fixing of the terminals 53 Annex C (norm ative) Touch current measurem ent in fault condition 54 Annex D (inform ative) Extrapolation of tem perature to tim e of shutdown 56 –4– I EC 621 35-1 : 201 © I EC 201 Annex E (inform ative) Exam ple of risk anal ysis and safety level requirement 57 E General 57 E Monitored hazards 57 E General m easures 57 E Typical hazards by type of equipm ent 57 E 4.1 General 57 E 4.2 Spot welding 58 E 4.3 Projection welding 59 E 4.4 Seam welding 60 E 4.5 Butt welding 60 Annex F (inform ative) I ndirect contact protection in resistance welding equipment 61 F.1 Protection against indirect contact by automatic disconnection of the supply 61 F General 61 F TN system 61 F TT systems 62 F.2 Automatic disconnection of suppl y in single phase a.c current equipment 63 F TN system 63 F 2 TT systems 64 F.3 Automatic disconnection of suppl y in d c current equipm ent operating at m edium frequency (inverter equipment) 64 F TN system 64 F TT systems 65 Bibliograph y 68 Figure – Measurement of welding circuit touch current Figure – Measurement of rms values Figure – Exam ple of m etal screen between windings of the suppl y circuit and the welding circuit 26 Figure – Exam ple of protective conductor connected directl y to the welding circuit (single-spot, a.c current equipment) 27 Figure – Exam ple of protective conductor connected directl y to welding circuits (m ulti-spot, a.c current equipm ent) 27 Figure – Exam ple of protective conductor connected directl y to welding circuits (m edium -frequency equipment) 28 Figure – Exam ple of protective conductor connected to welding circuits through impedances 29 Figure – Exam ple of protective conductor connected to welding circuits through auto-inductances 30 Figure – Exam ple of protective conductor connected to welding circuits through auto-inductances 30 Figure – Example of current operated RCD (a.c current equipment) 31 Figure 1 – Example of current operated RCD (m edium -frequency equipment) 32 Figure – Example of current operated residual current device and voltage relay 33 Figure – Example of current operated residual current device and safety-voltage relay 34 Figure – Example of safety voltage relay 35 Figure C.1 – Measuring network for weighted touch current 54 I EC 621 35-1 : 201 © I EC 201 –5– Figure C – Diagram for touch current m easurement on fault condition at operating temperature for single-phase connection of appliances other than those of class I I 55 Figure C.3 – Diagram for touch current m easurem ent on fault condition for threephase four-wire system connection of appliances other than those of class I I 55 Figure E – Structure of a m ounted machine 58 Figure E – Structure of a hand-held welding gun 58 Figure E – Structure of proj ection welding machinery 59 Figure E – Structure of seam welding machinery 60 Figure E – Structure of butt welding machinery 60 Figure F – Principle illustration of insulation fault 61 Figure F – I llustrations of TN systems 62 Figure F – I llustrations of TT systems 63 Figure F – Typical fault current 65 Figure F – Tim e-to-voltage reference curve 67 Table – Minim um clearances for overvoltage category I I I Table – Minim um creepage distances Table – I nsulation resistance Table – Dielectric test voltages Table – Minim um distance through insulation 25 Table – Continuity of the protective bonding circuit 37 Table – Lim its of temperature rise for windings 42 Table – Lim its of temperature rise for external surfaces of hand -held equipm ent 43 Table – Lim its of temperature rise for external surfaces of hand -guided equipment 43 Table – Limits of temperature rise for external surfaces of fixed equipm ent 43 Table B – Range of conductor dimensions to be accepted by the suppl y circuit term inals 52 Table B – Spacing between suppl y circuit term inals 53 –6– I EC 621 35-1 : 201 © I EC 201 INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON RE S I S T AN C E WE L D I N G E Q U I P M E N T – P a rt : S a fe t y re q u i re m e n ts fo r d e s i g n , m a n u fa c t u re a n d i n s ta l l a ti o n FOREWORD ) The I nternati on al Electrotechni cal Com m ission (I EC) is a worl d wid e organi zation for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all q uestions concerni ng stand ardi zati on in the el ectrical an d electronic fi elds To this en d an d i n additi on to other acti vities, I EC publish es I nternational Stan dards, Techn ical Specificati ons, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) an d Guides (h ereafter referred to as “I EC Publication(s)”) Th ei r preparation is entrusted to tech nical comm ittees; any I EC National Comm ittee interested in th e subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations liaising with th e I EC also partici pate i n th is preparation I EC collaborates closel y with the I ntern ational Org ani zation for Stand ardi zation (I SO) in accordance with conditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or agreem ents of I EC on technical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recom m endations for intern ational use an d are accepted by I EC Nati onal Com m ittees in that sense While all reasonable efforts are m ade to ensure that th e tech nical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for the way in which th ey are used or for an y m isinterpretation by an y en d user 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publications transparentl y to the m axim u m extent possibl e i n th eir national an d regi onal publications Any divergence between an y I EC Pu blication and the correspondi ng national or regi on al publ icati on shall be clearl y in dicated in the latter 5) I EC itself d oes not provi de an y attestation of conform ity I n depend ent certificati on bodies provide conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for an y services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that they h ave the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi du al experts an d m em bers of its technical com m ittees and I EC N ation al Com m ittees for any person al i nju ry, property d am age or other dam age of any n atu re whatsoever, wheth er d irect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publication or any oth er I EC Publications 8) Attention is drawn to th e N orm ative references cited in this publication Use of the referenced publ ications is indispensable for the correct applicati on of this publication 9) Attention is drawn to the possibility that som e of the elem ents of this I EC Publication m ay be th e subject of patent rig hts I EC shall not be held responsibl e for identifyi ng any or all such patent ri ghts I nternational Standard I EC 621 35-1 has been prepared by I EC technical committee 26: Electric welding This second edition cancels and replaces the first edition published in 2008 This edition constitutes a technical revision This edition includes the following significant technical changes with respect to the previous edition: – creepage distances for pollution degree are no longer valid (see Table 2); – insulation requirem ents for Class I I equipment are defined (see Table 3); – dielectric test voltage interpolation restriction lower limit is changed to 220 V and interpolation for control and welding circuit is clarified (see Table 4); – m aximum temperature for insulation systems are reviewed in accordance with current edition of I EC 60085 (see Table 7); I EC 621 35-1 : 201 © I EC 201 –7– – m arking of terminals is defined (see 3); – table for nom inal voltages of suppl y networks is changed adopting Table B of I EC 60664-1 : 2007 in place of the Table B values referenced in the previous edition to provide for equipment to be connected to both earthed and unearthed systems The change impacts the creepage and clearance distance requirements for som e supply voltage ratings (see Annex A); – touch current in fault condition are measurem ent procedures are clarified (see 6.4.4 and Annex C) – welding circuit touch current is defined (see 6); – touch current in norm al condition are clarified and m oved in protection against electric shock in norm al service (see 7); – heating test conditions are clarified (see ); – external surface tem perature rise lim itation is changed (see 2) The text of this standard is based on the following documents: FDI S Report on votin g 26/558/FDI S 26/570/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table This publication has been drafted in accordance with the I SO/I EC Directives, Part The list of all the parts of the I EC 621 35 series, under the general title Resistance welding equipment, can be found on the I EC website The comm ittee has decided that the contents of this publication will remain unchanged until the stability date indicated on the I EC website under "http: //webstore iec.ch" in the data related to the specific publication At this date, the publication will be • • • • reconfirm ed, withdrawn, replaced by a revised edition, or amended A bilingual version of this publication m ay be issued at a later date I M P O R T AN T – T h e ' c o l o u r i n s i d e ' th at it tai n s u n d e rs t a n d i n g c o l o u r p ri n t e r of c o l o u rs i ts wh i c h c o n te n ts l og o a re U s e rs on th e co ve r p ag e o f th i s c o n s i d e re d sh ou l d to t h e re fo re be p u b l i cati o n u s e fu l p ri n t th i s fo r i n d i c ate s th e d o cu m en t c o rre c t u sin g a –8– I EC 621 35-1 : 201 © I EC 201 RE S I S T AN C E WE L D I N G E Q U I P M E N T – P a rt : S a fe t y re q u i re m e n ts fo r d e s i g n , m a n u fa c t u re a n d i n s ta l l a ti o n S cop e This part of I EC 621 35 applies to equipment for resistance welding and allied processes and includes single and multiple welding stations which may be manuall y or autom atically loaded and/or started This part of I EC 621 35 covers stationary and portable equipment This part of I EC 621 35 specifies electrical safety requirements for design, manufacture and installation I t does not cover all non-electrical safety requirem ents (e g noise, vibration) This part of I EC 621 35 does not include electromagnetic com patibility (EMC) requirements, which are included in I EC 621 35-2 To com pl y with this standard, all safety risks involved in loading, feeding, operating and unloading the equipm ent, where applicable, should be assessed and the requirem ents of related standards should be observed N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, onl y the edition cited applies For undated references, the latest edition of the referenced document (including an y amendments) applies I EC 60204-1 : 2005, Safety of machinery – Electrical equipment of machines – Part : General requirements IEC 60364-4-41 :2005, Low-voltage electrical installations – Part 4-41 : Protection for safety – Protection against electric shock IEC 60364-6, Low-voltage electrical installations – Part 6: Verification IEC 6041 7-DB: 201 1 , Graphical symbols for use on equipment I EC 60445, Basic and safety principles for man-machine interface, marking and identification – Identification of equipment terminals, conductor terminations and conductors I EC 60529, Degrees of protection provided by enclosures (IP Code) I EC 60664-1 : 2007, Insulation coordination for equipment within low-voltage systems – Part : Principles, requirements and tests _ “DB” refers to the I EC on -lin e d atabase – 56 – I EC 621 35-1 : 201 © I EC 201 Annex D (informative) Extrapolation of temperature to time of shutdown When the tem perature at the instant of shutdown cannot be recorded, it is necessary to use an extrapolation to obtain this tem perature The procedure for such extrapolation is as follows: a) the tim e is marked at the instant of shutdown ; b) successive tem perature readings are taken, and the elapsed tim e from shutdown noted for each; c) a m inim um of four readings is taken for each tem perature to be extrapolated; d) using logarithmic/linear graph paper, the readings are plotted so that the tem perature is against the logarithmic scale, and the time from shutdown against the linear scale A straight line extending back to t = will give the extrapolated temperature at shutdown Alternative A m athematical regression anal ysis can be used as an alternative to the graphical method I f a linear regression is chosen, then the logarithms of the temperatures are used with the linear values of the reading times from the instant of shutdown The regression anal ysis is solved for the time t = and the antilogarithm taken to find the true temperature I EC 621 35-1 : 201 © I EC 201 – 57 – Annex E (informative) Example of risk analysis and safety level requirement E.1 General This annex describes possible m echanical hazards on resistance welding equipment Corresponding to the type of equipm ent, hazards vary The hazards are evaluated on the basis of I SO 41 21 -1 and I SO 3849-1 and examples given for measures to be taken These measures should be looked upon as one possible solution out of man y Hazards due to sparks and splatters are not dealt with in this annex E.2 Monitored hazards The following hazards on resistance welding equipm ent are monitored: a) b) c) d) e) squeezing squeezing squeezing squeezing squeezing E.3 of parts of the bod y between the electrodes or electrode wheels; of parts of the bod y between upper and lower platen; by accidentally dropping of tools from upper platen or the clamping device; between work piece and clam ping device; by retraction of electrode wheels General measures The following general m easures are taken: a) reduced closing or clam ping speed (for example, mm /s) b) reduced opening gap between tools or electrodes or clamping devices c) force reduction until gap is closed to an extent where no part of the bod y can enter (i e., mm between work piece and clamping device) d) necessity to hold welding gun or work piece with both hands E.4 E.4.1 Typical hazards by type of equipment General Hazardous areas are indicated by means of an arrow (see Figures E to E 5) Machine elements are identified by the following num bering force g enerati on system transform er 11 electrode wheel upper arm electrode hol der 12 han dle wel ding head electrode 13 finger defl ector lower arm platen 14 guid ing protective bar fram e 10 wheel h ead – 58 – E.4.2 I EC 621 35-1 : 201 © I EC 201 Spot welding E.4.2.1 M ounted machine IEC NOTE Num bers are d efin ed i n E Figure E.1 – Structure of a mounted machine Hazard 2a Result of risk evaluation category B or Additional m easures, wh ere applicable: operated by one or two push-button(s), light barrier E.4.2.2 Hand-held welding gu n 12 IEC NOTE Num bers are d efin ed i n E Figure E.2 – Structure of a hand-held welding gun Hazard 2a whilst m aintaining or changing electrodes Result of risk evaluation: category B Additional m easures where applicable: trigger lock for work on electrodes I EC 621 35-1 : 201 © I EC 201 E.4.3 – 59 – Projection welding IEC NOTE Num bers are d efin ed i n E Figure E.3 – Structu re of projection welding machinery Hazard: 2a, 2b, 2c, 2d Result risk evaluation Category or possibly at small tool weight and/or low welding force (due to severity of possible inj ury) Additional m easures: Operation start by two push buttons, self-supervising, light barrier self-supervising, movable protection shield On this equipment a special protection system for the set-up mode m ay be necessary – 60 – E.4.4 I EC 621 35-1 : 201 © I EC 201 Seam welding 1 2 10 10 11 11 10 10 11 13 14 IEC NOTE Num bers are d efin ed i n E Figure E.4 – Structu re of seam welding machinery Hazard 2a, 2e Result of risk evaluation: category or Additional m easures: installation of a m ovable (up and down) finger deflector (1 3) on the retracting side (held in position by its own weight) and a guiding protective bar (1 4) E.4.5 Butt welding 1 2 3 IEC NOTE Num bers are d efin ed i n E Figure E.5 – Structure of butt welding machinery Hazard 2c, 2d Result of risk evaluation: category or Additional measures: operation start by means of two push-buttons, light barrier, movable shield I EC 621 35-1 : 201 © I EC 201 – 61 – An n e x F (informative) I n d i re c t c o n ta c t p ro te c ti o n i n re s i s ta n c e w e l d i n g e q u i p m e n t F P ro t e c t i o n a g a i n s t i n d i re c t c o n t a c t b y a u t o m a t i c d i s c o n n e c t i o n o f t h e su ppl y F.1 G e n e l Protection against indirect contact prevent risk arising when a person touches a m etal part of the equipm ent (exposed conductive part) with an insulation fault The following Figures F.1 to F.3 explain in principal possible protective m easures against electric shock Id Uc IEC F i g u re F – P ri n c i p l e i l l u s t t i o n o f i n s u l a t i o n fa u l t Automatic disconnection of the suppl y is the most comm on solution used for protecti on against indirect contact I t is achieved by the rem oval of a touch voltage, appearing on the occurrence of an insulation fault, before the time of contact with a touch voltage can become hazardous Maxim um disconnecting tim e for installations are defined by I EC 60364-4-41 The type of disconnection device is selected depending on the type of earthing system of the installation I EC 60364-4-41 describes the m ain earthing system s and defines their protection rules; in this annex onl y TN an TT system s are considered I n TN and TT systems, an insulation fault between a live conductor and the equipm ent exposed conductive parts caused current flow to earth I n both cases, the touch voltage usually exceeds the maximum permissible values and requires an automatic disconnection of suppl y This protection provision requires the presence of a protective bonding circuit, connected to all exposed conductive parts that allow detection of the fault F.1 TN s ys t e m The neutral point of the voltage source (suppl y transformer) is earthed and the equipment protective conductor is connected direct to it – 62 – I EC 621 35-1 : 201 © I EC 201 TN –C TN –S L1 L2 L3 N PE L1 L2 L3 PEN RB RB IEC F i g u re F – I l l u s t t i o n s o f T N s ys te m s Two m ain types of TN system exist: – TN-S where equipm ent exposed conductive parts are connected to the voltage source earthed neutral by PE (protective conductor and neutral are separate); – TN-C where equipment exposed conductive parts are connected to the earthed neutral by PEN (protective conductor combined with the neutral conductor) I n the TN system , the fault current is equivalent to a short circuit The current is high as limited onl y by the fault-loop impedance; therefore, the circuit can be disconnected by an overcurrent protective device (circuit-breaker therm al or magnetic protection, fuses) For circuits which supply class I hand-held equipm ent or portable equipm ent, the maximum disconnecting tim e is 0, s (for equipm ent operating on network having a nom inal voltage to earth of 230 V) An higher disconnection tim e up to s is perm itted for stationary equipment under special conditions The ability of an overcurrent protective device to provide protection for indirect contact is verified at the installation design stage by calculating the fault currents for all the distribution circuits and verifying that the disconnection device operate in a sufficient tim e with that current I f due to long cables or low conductor cross-section the fault current is too low to properl y operate the overcurrent protection device, an additional RCD is used This RCD m ay be separate residual current device or be combined with circuit-breakers This solution is not applicable in installation with a TN -C earthing system, where the protective conductor and the neutral one are the same F.1 TT s ys t e m s The neutral point of the voltage source (supply transformer) is earthed by an electrode separate from that used for the equipm ent I EC 621 35-1 : 201 © I EC 201 – 63 – TT L1 L2 L3 N PE RB RA IEC F i g u re F – I l l u s t t i o n s o f T T s y s t e m s In the TT system, the fault current is low as limited by the earth resistance, so cannot be detected and cleared by standard overcurrent protective devices Therefore, different disconnection devices are provided in the installation, usually an RCD IEC 60364-4-41 specifies that the ability of an RCD to provide protection for indirect contact is assured selecting an RCD sensitivity lower that a value derived from m easured installation earth connection resistance ( R a ), by the formula: IΔn ≤ 50 Ra This assures sufficient protection as the device operates with a fault current generating a 50 V touch voltage A fault with a lower current will generate a touch voltage lower than 50 V, a fault with higher current will be detected and insulated by RCD in a shorter tim e RCDs have a tripping tim e that is defined by I EC standards and related to the ratio between the fault current and the sensitivity value I EC 60364-4-41 requires that de-energizing by the RCDs shall occur in less than s The tripping times of RCDs are generall y lower than those required in the m ajority of situations I n order to increase availability of electrical power, the use of several RCDs ensures time and current discrimination on tripping F F.2 Au t o m a t i c d i s c o n n e c t i o n o f s u p p l y i n s i n g l e p h a s e a c c u rre n t e q u i p m e n t TN s ys t e m As described above, overcurrent protective device are usuall y used as disconnecting device for indirect contact protection Resistance welding equipment are characterized by very high instantaneous current com pared to the continuous equivalent current Therefore high setting of circuit-breaker trip current or use of delayed fuses (type aM) are required, while fuses used in installation for short-circuit protection are usuall y of gG type The installation design shall take care of this providing sufficient low fault loop im pedence to assure that the circuit-breaker or fuses operate in case of fault within the specified tim e (for example, using suppl y and PE cables with a sufficient cross-section) – 64 – I EC 621 35-1 : 201 © I EC 201 I f the required conditions cannot be met, an additional residual current device is used (apart from installation with a TN-C earthing system ) I n this situation, the following considerations regarding use of RCD in TT system s appl y F 2 TT system s As described above, residual-current devices are usuall y used as disconnecting devices for indirect contact protection The operation capability of an RCD depends on the fault current waveform I EC 60755 defines three types of RCD depending on the characteristics of the fault current In the case of fault between the input circuit and the welding circuit in typical single-phase a c equipment, the fault current is sinusoidal; therefore types AC, A and B RCDs are appropriate An yway, other circuit faults can generate a different fault waveform that requires a different RCD selection Onl y the m anufacturer knows the possible fault current waveform of its equipment and can incorporate the device in the equipment or specify which type of RCD is capable of assuring proper operation F F Autom ati c di scon necti on of suppl y i n d c current equi pment operati ng at m edi um frequency (i n verter eq ui pm ent) TN system All the considerations above for a.c single-phase equipment appl y also to d.c current equipm ent operating at m edium frequency; m oreover, other important factors have to be considered The most com mon fault is between the inverter output to ground, typicall y by a fault in the welding transform er insulation This type of fault requires additional consideration described below The touch voltage in case of fault is higher than in n etwork frequency fault as the protective conductor im pedance is higher at the inverter frequency (typicall y kH z to 20 kH z) The fault current may be limited in tim e by the inverter as it is present only when the equipm ent execute the welding process (i e , when the welding transform er is supplied) Additionall y, it has to be considered that the fault current am plitude m ay be limited by – the current supplied by the inverter may be electronicall y limited to a maximum permissible value (for example, by the welding current adjustment); – the protective conductor impedance (it is higher than 50 H z impedance value as the fault current have frequency components of kH z to 20 kH z) These fault current times and amplitude limitations can avoid the circuit-breaker or fuse operation in case of fault It shall also be considered that the reduction of the fault current time and magnitude correspond to a reduced touch voltage therefore to a reduced risk The inverter can provide a protection against short circuits between phases at the output that interrupt the suppl y of current to the transformer I n TN system s this device does not protect I EC 621 35-1 : 201 © I EC 201 – 65 – persons against indirect contact under all circum stances I n fact, the im pedance of the fault at the inverter frequency may lim it the current to a value that is below the inverter’s protection threshold F F TT system s Gen eral As described above, residual-current device are usuall y used as disconnecting device for indirect contact protection I n the case of fault between the input circuit and the welding circuit of typical inverter equipm ent, the fault current is non-sinusoidal I t is com posed of the inverter switching frequency and the d.c bus voltage to ground frequency (typicall y 000 H z and 50 H z) IEC Fi g u re F – Typi cal fau l t cu rren t Frequency content of the fault current depends on man y factors, including inverter switching frequency, type of inverter input stage and equipment welding current adj ustm ent The com plex shape of the fault current (see Figure F 4) requires the use of a type A or B RCD suitable for the frequency content of the fault current An yway other circuit faults generate different fault waveforms that can require different RCD selection; for example, d.c bus to earth fault generates a fault current that requires type B RCD Only the m anufacturer knows the possible fault current waveform of its equipment (i.e., its frequency content) and can incorporate the device in the equipm ent or specify which type of RCD is capable of assuring proper operation The inverter can provide a protection against short circuits between phases at the output that interrupt the suppl y of current to the transformer I n TT system s this device does not protect persons against indirect contact as the impedance of the fault at the inverter frequency is very high and limit the current to a value that is far below the inverter’s protection threshold (the fault current may be of a few am ps) – 66 – F.3.2.2 I EC 621 35-1 : 201 © I EC 201 RCD sensitivity, break time and operating frequency The patho-ph ysiological effects of electrical current flowing in the bod y depend on its magnitude and duration RCD are typicall y designed for network frequency operation and provide current related operating time that are defined by I EC standards based on pathoph ysiological effects RCD sensitivity is expressed as the rated residual operating current, I∆ n Preferred values have been defined by I EC, m aking it possible to divide RCDs into three groups according to their I∆ n value: – high sensitivity (H S): mA – m A – 30 mA; – medium sensitivity (MS): 0, A – 0, A – 0, A – A; – low sensitivity (LS): A –1 A – 30 A High sensitivity (H S) is m ost often used for additional direct-contact protection The other sensitivities (MS and LS) are usuall y used for protection against indirect contacts RCD are also used in installations for fire protection and protection of the equipment When the RCD is used for protection against indirect contact, its sensitivity is not directl y related to current flowing into the bod y but selected according to installation earth connection resistance The current flowing through the hum an bod y depends m ainl y on environmental conditions and on the touch voltage The current flowing through the hum an bod y is influenced also by the frequency, as the bod y im pedance is highl y frequency dependant When an RCD is used for indirect contact protection, it has to disconnect the suppl y within a time that is related to the prospective touch voltage The reference curves used by I EC 60364-4-41 are derived from I EC 60479 series together with an explanation of the derivation of the requirements Duration, ms I EC 621 35-1 : 201 © I EC 201 – 67 – 000 000 L 00 10 10 00 000 Prospecti ve touch voltag e Ut , V IEC Figu re F – Tim e-to-vol tag e referen ce cu rve IEC 60364-4-41 provides m eans of com pliance based on the selection of RCD sensitivity corresponding to a fault current generating a 50 V touch voltage and allowing a m axim um disconnection tim e of s This satisfies the requirement for an y value of touch voltage and fault current Time-to-voltage reference curve is shown in Figure F In order to prevent undesired tripping, an RCD m ay be protected against high-frequency currents with low-pass filters; therefore, an RCD device m ay present low sensitivity (or increased break tim e) to fault currents on inverter resistance welding equipment The frequency content of the fault current is, therefore, a m ost im portant factor Standards specify that type B RCD shall operate with frequencies up to kH z; therefore, the use of this device satisfies the requirem ent for inverter resistance welding equipment operating up to kH z The ability of other RCD types or equipment operating at higher frequencies shall be verified case by case as different RCDs present different sensitivity and operation time – 68 – I EC 621 35-1 : 201 © I EC 201 Bibliography I EC 60050-851 : 2008, International Electrotechnical Vocabulary (IEV) – Part 851: Electric welding I EC 60085, Electrical insulation – Thermal evaluation and designation I EC 601 2, Method for the determination of the proof and the comparative tracking indices of solid insulating materials IEC 60364 (all parts), Low-voltage electrical installations IEC 60479 (all parts), Effects of current on human beings and livestock IEC 60755, General requirements for residual current operated protective devices IEC 60990, Methods of measurement of touch current and protective conductor current I EC/TR 61 200-41 3, Electrical installation guide – Part 413: Protection against indirect contact – Automatic disconnection of supply I EC/TS 61 201 , Use of conventional touch voltage limits – Application guide I EC 621 35-2, Resistance welding equipment – Part 2: Electromagnetic compatibility (EMC) requirements I SO 5826, Resistance welding equipment – Transformers – General specifications applicable to all transformers I SO 5828, Resistance welding equipment – Secondary connecting cables with terminals connected to water-cooled lugs – Dimensions and characteristics I SO 8205-1 , Water-cooled secondary connection cables for resistance welding – Part 1: Dimensions and requirements for double-conductor connection cables I SO 8205-2, Water-cooled secondary connection cables for resistance welding – Part 2: Dimensions and requirements for single-conductor connection cables I SO 21 00, Safety of machinery – General principles for design – Risk assessment and risk reduction I SO 3732-1 , Ergonomics of the thermal environment – Methods for the assessment of human responses to contact with surfaces – Part 1: Hot surfaces I SO 3732 (all parts), Ergonomics of the thermal environment – Methods for the assessment of human responses to contact with surfaces I SO 41 21 -1 , Safety of machinery – Risk assessment – Part 1: Principles _ _ This publication was withd rawn INTERNATIONAL ELECTROTECHNICAL COMMISSI ON 3, rue de Varembé PO Box 31 CH-1 21 Geneva 20 Switzerland Tel: + 41 22 91 02 1 Fax: + 41 22 91 03 00 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