BS 7822-3-1995 Insulation coordination for equipment within low-voltage systems - Use of coatings to achieve insulation coordination of printed board assemblies《低压系统设备的绝缘配合 第3部分 印制.pdf

1、BRITISH STANDARD BS 7822-3: 1995 IEC 664-3: 1992 Insulation coordination for equipment within low-voltage systems Part 3: Use of coatings to achieve insulation coordination of printed board assembliesBS7822-3:1995 This British Standard, having been prepared under the directionof the Electrotechnical

2、 Sector Board, was published underthe authority of the Standards Board and comesintoeffect on 15November1995 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference GEL/28/1 Draft for comment 88/22388 DC ISBN 0 580 24554 3 Committees responsible for this Bri

3、tish Standard The preparation of this British Standard was entrusted by Technical Committee GEL/28, Insulation coordination, to Subcommittee GEL/28/1, Insulation coordination for low voltage equipment, upon which the following bodies were represented: Association of Control Manufacturers TACMA (BEAM

4、A Ltd.) Association of Manufacturers of Domestic Electrical Appliances Association of Manufacturers Allied to the Electrical and Electronic Industry (BEAMA Ltd.) British Electrotechnical Approvals Board Department of Trade and Industry (Consumer Safety Unit, CA Division) Electrical Installation Equi

5、pment Manufacturers Association Electricity Association GAMBICA (BEAMA Ltd.) Institute of Electrical Engineers Transmission and Distribution Association (BEAMA Ltd.) Amendments issued since publication Amd. No. Date CommentsBS7822-3:1995 BSI 08-1999 i Contents Page Committees responsible Inside fron

6、t cover National foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Definitions 2 4 Design requirements 2 5 Test specimens 3 6 Tests 5 Annex A (normative) Test sequence for type A coating 10 Annex B (normative) Test sequence for type B coating 10 Annex C (informative) Measuring the insu

7、lation distance of a coated printed board 10 Figure 1 Test specimen 8 Figure 2 Examples of land configurations 9 Figure C.1 Measurement of the insulation distance 12 Table 1 Degrees of severities for rapid change of temperature 5 List of references Inside back coverBS7822-3:1995 ii BSI 08-1999 Natio

8、nal foreword This British Standard has been prepared by Technical Committee GEL/28/1 and is identical with IEC664-3:1992 Insulation coordination for equipment within low-voltage systems Part 3: Use of coatings to achieve insulation coordination of printed board assemblies, published by the Internati

9、onal Organization for Standardization (IEC). IEC 664 has the status of a basic safety publication in accordance with IECGuide104. It is envisaged that BS7822 will consist of the following parts under the general title Insulation coordination for equipment within low-voltage systems. Part 1: Principl

10、es, requirements and tests; Part 2: Concise requirements for clearances, creepage distances and solid insulation; (Under consideration) Part 3: Use of coatings to achieve insulation coordination of printed board assemblies; (This Part) Part 4: Application guide. (Under consideration) Cross-reference

11、s Publications referred to Corresponding British Standard IEC 62-2-3:1969 BS 2011 Environmental testing Part 2.1 Tests Part 2.1Ca:1977 Test Ca. Damp heat, steady state IEC 68-2-14:1984 Part 2.1N:1985 Test N. Change of temperature IEC 112:1979 BS 5901:1980 Method of test for determining the comparati

12、ve and the proof tracking indices of solid insulating materials under moist conditions IEC 194:1988 BS 4727 Glossary of electrotechnical, power, telecommunications, electronics, lighting and colour terms Part 1 Terms common to power, telecommunications andelectronics Group 11:1991 Printed circuits I

13、EC 216-2 BS 5691 Guide for the determination of thermal endurance properties of electrical insulating materials Part 2:1979 List of materials and available tests IEC 249-3-3:1991 BS 4584 Metal-clad base materials for printed wiring boards Part 103 Special materials used in connection with printed ci

14、rcuits Section 103.3:1992 Specification for permanent polymer coating materials (solder resist) for use in the fabrication of printed boards BS 6221 Printed wiring boards IEC 326-2:1990 Part 2:1991 Methods of test IEC 326-4:1980 Part 4:1982 Method for specifying single and double sided printed wirin

15、g boards with plain holesBS7822-3:1995 BSI 08-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal

16、 obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages1to 12, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table

17、on the inside front cover.iv blankBS7822-3:1995 BSI 08-1999 1 Introduction This part of IEC 664 applies to rigid printed board assemblies protected by a coating of insulating material on one side or both sides of the printed board. It deals with the influence of these coatings on the insulation prop

18、erties. It does not cover repaired printed board assemblies. Between any two uncoated conductive parts and over the coating between conductive parts, the clearance and creepage distance requirements of IEC664-1 apply. The coatings considered in this part are permanent protective coatings, such as th

19、e following: permanent solder resists (wet or dry film) using screen printing or photo definable processes; coverlayers, i.e. insulating protective layers placed on the surface of a printed board; conformal coating, i.e. insulating coating applied to printed board assemblies. Coating considered in t

20、his part may also include such encapsulation as moulding or potting. Technical Committees have to consider the influence of overheating of conductors and components, especially under fault conditions, and to decide if any additional requirements are necessary. Not all coating systems in use are capa

21、ble of improving insulation properties. The tests specified in this part can be used to determine the suitability of the coating systems. Safe performance of printed board assemblies is dependent upon a precise and controlled manufacturing process for the application of the coating. Requirements for

22、 quality control, e.g. by sampling tests, should be considered by Technical Committees. 1 Scope This part of IEC 664 applies to rigid printed board assemblies with an insulating coating applied to one or both sides of the printed board. Such coatings are used to provide insulation and to protect the

23、 microenvironment of the printed board assembly surface against pollution, for the purpose of insulation coordination. It describes the requirements and test procedures for printed board assemblies provided with coatings. This part covers two types of coatings: type A coating only provides protectio

24、n against pollution. The clearance and creepage distance requirements of IEC664-1 apply to the printed board assembly under the coating; type B coating provides protection against pollution and insulation. There are no requirements for clearances and creepage distances under the coating. Only the re

25、quirements of IEC664-1 for solid insulation apply. NOTE 1For type B coating, the conductors are embedded in solid insulation consisting of the base material and the coating. NOTE 2Clearances and creepage distance requirements apply to all uncoated parts of the board and between conductive parts over

26、 the coating. The principles in this part are applicable to functional and basic insulation. NOTE 3For supplementary and reinforced insulation, additional requirements, which are under consideration, may apply. 2 Normative references The following standards contain provisions which, through referenc

27、e in this text, constitute provisions of this part of IEC664. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this part of IEC664 are encouraged to investigate the possibility of applying the most recent edition

28、s of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. IEC 68-2-1:1990, Environmental testing Part2:Tests Tests A: Cold. IEC 68-2-2:1974, Environmental testing Part2:Tests Tests B: Dry heat. IEC 68-2-3:1969, Environmental testing Par

29、t2:Tests Test Ca: Damp heat, steady state. IEC 68-2-14:1984, Environmental testing Part2:Tests Test N: Change of temperature. Amendment 1 (1986). IEC 112:1979, Method for determining the comparative and the proof tracking indices of solid insulating materials under moist conditions. IEC 194:1988, Te

30、rms and definitions for printed circuits. IEC 216, Guide for the determination of thermal endurance properties of electrical insulating materials. IEC 249-3-3:1991, Base materials for printed circuits Part 3: Special materials used in connection with printed circuits Specification No.3: Permanent po

31、lymer coating materials (solder resist) for use in the fabrication of printed boards. IEC 326-2:1990, Printed boards Part 2: Test methods. BS7822-3:1995 2 BSI 08-1999 IEC 326-4:1980, Printed boards Part4:Specification for single and double sidedprinted boards with plain holes. Amendment1(1989). IEC

32、364-4-443:1990, Electrical installations of buildings Part 4: Protection for safety Chapter44: Protection against overvoltages Section 443: Protection against overvoltages of atmospheric origin or due to switching. IEC 664-1:1992, Insulation co-ordination for equipment within low-voltage systems Par

33、t1:Principles, requirements and tests. 3 Definitions In addition to the definitions in IEC 664-1, the following definitions apply for the purpose of this part of IEC664: 3.1 base material insulating material upon which the pattern may be formed IEC194-02-01 3.2 printed board base material cut to siz

34、e containing all holes andbearing at least one conductive pattern IEC194-01-03 it includes single and double-sided, multilayer, flexible and flexible multilayer boards 3.3 printed board assembly printed board with electrical and mechanical components and or other printed boards attached to it, with

35、all manufacturing processes, soldering, coating, etc. completedIEC194-01-20 3.4 conductor single conductive path in a conductive pattern IEC194-01-28 3.5 coating solid insulating material laid on one or both sides of the surface of the printed board. Coating can be a varnish, a dry film applied to t

36、he printed board or can be achieved by thermal deposition NOTECoating and base material of the printed board form an insulating system that may have properties similar to solid insulation. 3.6 solid insulation solid insulating material interposed between two conductive parts NOTEIn the case of a pri

37、nted board with a coating, solid insulation consists of the board itself as well as the coating. In other cases, solid insulation consists of the encapsulating material. 3.7 insulation distance the insulation distance of a coated printed board is the shortest distance between conductive parts locate

38、d on the base material (see Figure C.1 ofAnnex C) 3.8 spacing spacing is any combination of clearances, creepage distances and insulation distances 4 Design requirements 4.1 Principles Spacings less than those specified in IEC664-1 are permitted between conductors under coatings if specified require

39、ments and tests are met. The requirements and relaxations are also applicable where coatings are applied to substrates and assemblies which are similar to printed wiring boards. NOTEExamples of such substrates are hybrid integrated circuits and thick-film technology. 4.1.1 Application range regardin

40、g environment The requirements of this part apply to printed board assemblies where the micro-environment at the surface of the coating is not worse than pollution degree2for type A coating and pollution degree3for type B coating. 4.1.2 Types of coating Coating or encapsulation may be used in two wa

41、ys to allow reduced spacings between conductors: type A coating, by improving the environment for spacings between printed wiring conductors under the coating to pollution degree1; type B coating, by enclosing the conductors in solid insulation so that the clearance and creepage distance requirement

42、s are not applicable between conductors under the coating. Coating can be effective between two conducting parts if it covers either one or both conductive parts, together with at least80% of the creepage distance between them. NOTEAs a result, some coated printed board assemblies can be used with h

43、igher voltage or reduced distances between conductive parts compared to the same printed board assembly when uncoated.BS7822-3:1995 BSI 08-1999 3 Clearance and creepage distance requirements according to IEC664-1 apply to all uncoated parts of the printed board assembly and between conductive part o

44、ver the coating. 4.2 Voltage stresses 4.2.1 Steady-state stresses Steady-state stresses are long-term stresses due to the working voltage. Solid insulation and creepage distances of functional insulation shall be designed to withstand the working voltage across the insulation. For creepage distances

45、 of basic insulation of circuits immediately energized from the supply mains, the voltage reference for Table 4 of IEC664-1 shall be taken from Table 3a or Table 3b of IEC664-1. The insulation shall also withstand the recurring peak value of the working voltage and partial discharges shall not be ma

46、intained. Therefore, the partial discharge extinction voltage shall be higher than the recurring peak value of the working voltage. NOTENon-periodic transient overvoltages are not expected to have significant cumulative effect on solid insulation. However, transient overvoltages which are produced f

47、requently, although irregularly, within the equipment should be taken into account, since they can cause partial discharges leading to a failure. 4.2.2 Transient stresses due to overvoltage The impulse withstand voltage of basic insulation on a printed board assembly shall take into account: mains-b

48、orne transients, in accordance with Table 44B and Table 44C of IEC364-4-443; transients from other external sources, such as a telecommunication line or aerial; internally generated overvoltages. If the coated printed board assembly is part of an equipment, its rated impulse voltage shall be based o

49、n the maximum transient overvoltage that can occur at the interface of the printed board assembly. 4.2.3 Temporary stresses due to overvoltages Temporary overvoltage stresses due to faults between the high-voltage and low-voltage distribution systems are specified inIEC 364-4-443. 4.2.4 Temporary stresses due to power frequency dielectric testing Since power frequency test voltages may exceed the stresses described in4.2.1 to4.2.3, coated printed board assemblies which are part of an equipment shall