1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD BS 7797 : 1998 ICS 91.140
2、.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Specification for Industrial duct heaters using metal-sheathed elementsThis British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards B
3、oard and comes into effect on 15 May 1998 BSI 1998 The following BSI references relate to the work on this standard: Committee reference PEL/27 Draft for comment 92/04452 DC ISBN 0 580 29535 4 BS 7797 : 1998 Amendments issued since publication Amd. No. Date Text affected Committees responsible for t
4、his British Standard The preparation of this British Standard was entrusted to Technical Committee PEL/27, Electroheating, upon which the following bodies were represented: Association of Manufacturers Allied to the Electrical and Electronic Industry (BEAMA Ltd.) British Glass Manufacturers Confeder
5、ation British Industrial Furnace Constructors Association British Lighting Association for the Preparation of Standards (BRITLAPS) British National Committee for Electroheat British Steel plc Committee for Electrical Equipment for Use in Flammable Atmosphere (BEAMA Ltd.) Electric Trace Heating Indus
6、try Council (ETHIC) Electricity Association Energy Industries Council Engineering Equipment and Materials Users Association Engineering Industries Association Health and Safety Executive Induction and Dielectric Heating Manufacturers Association Institution of Electrical Engineers Lighting Industry
7、Federation Ltd.BS 7797 : 1998 BSI 1998 i Contents Page Committees responsible Inside front cover Foreword ii Specification 1 Scope 1 2 References 1 3 Definitions 1 4 Heating elements 2 5 Rating 2 6 Degree of protection 2 7 Electrical insulation 2 8 Thermal insulation 2 9 Construction 3 10 Supply con
8、nections 3 11 Terminations for external conductors 4 12 Provision for earthing 6 13 Internal wiring 7 14 Mounting of components 8 15 Screws and connections 8 16 Creepage distances, clearances, and distances through insulation 9 17 Controls 10 18 Labels and warning notices 10 19 Routine testing 10 20
9、 Instructions 11 21 Marking 11 Annexes A (normative) Methods of test 12 B (informative) Guidance for installation and maintenance of duct heaters 13 Tables 1 Power output 2 2 Minimum thickness of metallic enclosures 3 3 Terminal sizes 4 4 Fastening strength of terminals 4 5 Dimensions of pillar term
10、inals 5 6 Dimensions of screw terminals 6 7 Dimensions of stud terminals 6 8 Minimum spacings 8 9 Creepage distances and clearances 9 10 Temperature marking for supply connections 10 11 Symbols for marking 11 A.1 Torque values for screw torque test 12 A.2 Torque values for screw torque test, for ter
11、minals described in 11.2.3 and 11.3.3 13 List of references Inside back coverii BSI 1998 BS 7797 : 1998 Foreword This British Standard has been prepared by Technical Committee PEL/27. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standard
12、s are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 14, an inside back cover and a back cover. BSI 1998
13、 1 BS 7797 : 1998 Specification 1 Scope This British Standard specifies requirements for industrial electric heaters with a rated voltage of up to 440 V, using metal-sheathed elements and installed in a duct run, for heating in forced air systems or for heating of non-flammable gases. The heaters ma
14、y have fixed, replaceable or removable elements. 2 Normative references This British Standard incorporates, by dated or undated reference, provisions from other publications. These normative references are made at the appropriate places in the text and the cited publications are listed on the inside
15、 back cover. For dated references, only the edition cited applies: any subsequent amendments to or revisions of the cited publication apply to this British Standard only when incorporated in the reference by amendment or revision. For undated references, the latest edition of the cited publication a
16、pplies, together with any amendments. 3 Definitions For the purposes of this British Standard, the following definitions apply. 3.1 (metal-sheathed heating) element A heating assembly comprising a resistance alloy within, and insulated from, a tubular metal sheath. 3.2 duct heater An assembly of met
17、al-sheathed heating element(s), associated controls and wiring, installed in a duct run. 3.3 terminal enclosure The enclosure in which the elements are terminated. NOTE. Other electrical equipment can be contained within the enclosure; for example, thermostats, pressure switches, contactors, transfo
18、rmers, fuses. 3.4 fixed element An element which is permanently attached to its supporting body by adhesive bonding, soldering, brazing or welding. 3.5 replaceable element An element which can only be removed with the aid of a tool, normally after removal of the element bundle from its containment d
19、ucting. 3.6 removable element An element which can be removed without the need for removing the element bundle from its containment ducting. 3.7 ducting The sheet-metal fabrication through which the air or non-flammable gases pass, and into which the element bundle is inserted. 3.8 mounting plate Th
20、e plate to which the element bundle or containment pocket is attached. 3.9 rated voltage The voltage assigned to the heater by the manufacturer. 3.10 rated power The wattage, at rated voltage, assigned to the heater by the manufacturer. 3.11 thermal insulation A material or system that has the prope
21、rty of resisting the transfer of heat. 3.12 thermostat A temperature-sensing device, the operating temperature of which may be either fixed or adjustable and which, during normal operation, keeps the temperature of the air or gases between certain limits by opening or closing a heater circuit. 3.13
22、temperature limiter A temperature-sensing device, the operating temperature of which may be either fixed or adjustable and which, during normal operation, operates by opening or closing a heater circuit when the temperature reaches a predetermined value. NOTE. A temperature limiter does not make the
23、 reverse operation during the normal duty cycle of the heater. It may or may not require manual resetting. 3.14 thermal cut-out A device which, during abnormal operation, limits the temperature of a heater, or of parts of it, by opening the circuit or by reducing the current, and which is so constru
24、cted that its setting cannot be altered by the user. 3.15 basic insulation Insulation applied to live parts to provide basic protection against electric shock. NOTE. Basic insulation does not necessarily include insulation used exclusively for functional purposes. 3.16 supplementary insulation Indep
25、endent insulation applied in addition to basic insulation, for protection against electric shock in the event of a failure of the basic insulation. 3.17 double insulation Insulation comprising both basic insulation and supplementary insulation. 3.18 reinforced insulation A single insulation system a
26、pplied to live parts that provides a degree of protection against electric shock equivalent to double insulation. NOTE. The term insulation system does not imply that the insulation is one homogeneous piece. It may comprise several layers that cannot be tested singly.2 BSI 1998 BS 7797 : 1998 3.19 s
27、tud terminal Screw-type terminal in which the conductor is clamped under one or two nuts. The clamping pressure may be applied directly by a suitably shaped nut or through an intermediate part, such as a washer, clamping plate or anti-spread device. 3.20 pillar terminal Screw-type terminal in which
28、the conductor is inserted into a hole or cavity, where it is clamped under the shank of a screw or screws. The clamping pressure may be applied directly by the shank of the screw or through an intermediate part to which pressure is applied by the shank of the screw. 3.21 screw terminal Screw-type te
29、rminal in which the conductor is clamped under a bolt and washer, the bolt passing through a fixed nut or threaded bush. 3.22 creepage distance The path between two conductive parts, or between a conductive part and the bounding surface of the element, measured across the surface of the insulating m
30、aterial. 3.23 clearance The distance between two conductive parts, or between a conductive part and the bounding surface of the element, measured through air. 4 Heating elements All the heating elements shall conform to BS 7351 : 1990. 5 Rating 5.1 Rated voltage Heaters shall be rated for a line vol
31、tage not greater than 440 V. NOTE. The requirements of this standard are based on the assumption that, in normal use, the voltage between the supply lines and neutral does not exceed 254 V. 5.2 Rated power The actual power output from the heater at the operating temperature, on application of the ra
32、ted voltage, shall not vary from the rated power output by more than the tolerances given in table 1, when verified in accordance with A.1. Table 1. Power output Rated power kW Tolerance % 0t o5 0 7.5 $ 51 5.5 6 Degree of protection The minimum degree of protection provided by heater enclosures shal
33、l be in accordance with IP 20 of BS EN 60529 : 1992. 7 Electrical insulation 7.1 The mounting of electrically insulating parts shall be designed so as to prevent breakage or damage due to expansion and contraction. 7.2 Electrically insulating washers, bushings and the like, which are integral parts
34、of the heater, and bases or supports of the mounting of current-carrying parts shall be of a moisture-resistant material which will not be damaged by the temperatures to which they will be subjected under conditions of actual use. 7.3 The insulation between any parts operating at extra-low voltage a
35、nd other live parts, and between the core of the isolating transformer and other metal parts, shall be as specified in BS 3535 : Part 1 and Part 2. 7.4 Parts which serve as supplementary insulation or reinforced insulation shall either: a) be fixed in such a way that they cannot be removed without b
36、eing seriously damaged; or b) be designed so that they cannot be replaced in an incorrect position, and so that, if they are omitted, the appliance is rendered inoperable or manifestly incomplete. NOTE 1. Sleeving may be used as supplementary insulation on internal wiring, if it can only be removed
37、by breaking or cutting, or if it is clamped at both ends. NOTE 2. Lining metal enclosures with a coating of lacquer, or with other material in the form of a coating which can be easily removed by scraping, is not deemed to meet this requirement. 7.5 Inside the terminal enclosure, the sheath of a fle
38、xible cable or cord shall only be used as supplementary insulation where it is not subject to undue mechanical or thermal stresses and if its insulating properties are not less than those specified for the sheaths of flexible cables and cords in BS 6004, BS 6007, or BS 6500. 8 Thermal insulation 8.1
39、 Thermal insulation materials shall not make contact with the heating element. 8.2 Where terminal enclosures are stood off from the mounting plate to give cooling via natural convection, the stand-off areas shall not be thermally insulated. BSI 1998 3 BS 7797 : 1998 Table 2. Minimum thickness of met
40、allic enclosures Material Reinforced flat surfaces Surfaces to which a wiring system is to be connected on site Unreinforced flat surfaces mm mm mm Die-cast steels 1.2 2.0 Cast malleable iron 1.6 2.4 Other cast metal 2.4 3.2 Uncoated sheet steel 0.66 0.81 0.66 Galvanized sheet steel 0.74 0.86 0.74 N
41、on-ferrous sheet steel 0.91 1.14 0.91 9 Construction NOTE. Heaters should be so constructed that they operate in all positions to be expected in normal use. Any limitations of use should be specified by the manufacturer. 9.1 Heaters shall be constructed so that, after being removed for servicing or
42、maintenance, they can be refitted correctly with normal tools. 9.2 A thermal cut-out or temperature limiter shall be provided. The sensor shall be mounted so as to protect the complete heater unit. 9.3 If element surface temperature monitors are fitted, they shall be attached to the element sheath b
43、y brazing, welding or mechanical clamping. 9.4 Heaters shall be provided with an enclosure. 9.5 The minimum thickness of metallic enclosures shall be as stated in table 2. 9.6 Non-metallic enclosures shall conform to the appropriate glow-wire test requirements of BS 6458 : Section 2.1. NOTE. Special
44、 consideration should be given to any non-metallic enclosure to ensure that it has sufficient physical strength, and that it has adequate resistance to impact, moisture absorption, corrosion and to distortion with respect to thermal ageing. 9.7 All parts of the heater in contact with air or gases sh
45、all be manufactured from materials resistant to service corrosion or protected by a corrosion-resistant finish. Details of any protective finish, including its method of application and recommended intervals for recoating, shall be specified in the maintenance instructions. 9.8 All external parts op
46、en to the atmosphere shall be manufactured from materials resistant to the atmosphere or protected by a corrosion-resistant finish. NOTE. Particular care should be taken in the selection of the materials used within the terminal enclosures, where airborne vapours or corrosive gases may exist. Detail
47、s of any protective finish, including its method of application and recommended intervals for recoating, shall be specified in the maintenance instructions. 9.9 Internal surfaces shall be smooth and free from sharp edges, burrs, flashes and the like, which might abrade the insulation of the wiring.
48、9.10 Where terminal enclosures are stood off from the flange plate to allow cooling by natural convection, suitable safety guards shall be fitted. 9.11 Spacers intended to prevent the element from overheating the duct walls shall be so fixed that it is not possible to remove them from the outside of
49、 the heater by means of a screwdriver or spanner. 9.12 The heaters shall be so constructed that the setting of thermostats or other control devices cannot be accidentally altered. 9.13 The location and mounting of any integral controls shall be such as to protect them from damage when in use and when the heater is removed for servicing. 9.14 Handles, knobs, grips and levers shall be securely fixed so that they will not work loose in normal use. If handles or knobs are used to indicate the position of switches or similar components, it shall not be possible to fix them
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