6 CONSTRUCTION

6.1 GENERAL

6.1.1 A manual station shall be constructed for its intended installation and use and shall comply with the construction requirements contained in this Section, unless, where permitted by test, the construction is determined to be equivalent to these requirements.

6.1.2 Unless specifically indicated otherwise, the construction requirements specified for a product shall also apply to any accessories with which it is to be employed.

6.1.3 The minimum size of a manual station shall be 77 cm².

6.1.4 The outer surface of the manual station used to initiate a fire alarm signal shall be permanently coloured red. Refer to Section 12, Ancillary Use Manual Stations.

6.1.5 If an additional alarm visual indicator is provided, it shall be positioned within the operating face or within the front face of the manual station. The visual indicator shall be:

A      Red;

B      Visible from a distance of 2 m directly in front of the manual station, in an ambient light intensity up to 500 lx; and

C      Identify the manual station which initiated an alarm until the alarm condition is reset.

6.1.6 Where other conditions of the manual station may be visually indicated, they shall be clearly distinguishable from the alarm indication, except when the manual station is switched into a service mode.

6.2 FRAME AND ENCLOSURE

6.2.1 A manual station shall be so formed and assembled that it has the strength and rigidity necessary to resist the abuses to which it is likely to be subjected, without adversely affecting its performance, due to total or partial collapse with resulting reduction of spacings, loosening or displacement of parts, or development of other conditions which could impair operation of the device and increase the risk of fire or electrical shock. See Subsection 8.17, Mechanical Strength Tests for Enclosures.

6.2.2 Electrical parts of a manual station shall be so located or enclosed that suitable protection to a person against accidental contact with uninsulated hazardous live parts is provided.

6.2.3 Operating parts, such as contacts and similar parts, shall be adequately protected against mechanical damage and against fouling by dust or by other materials that might adversely affect their normal operation.

6.2.4 Provision shall be made for securely mounting the manual station in position. Bolts, screws, or other parts used for mounting shall be independent of those used for securing component parts of the assembly.

6.2.5 An opening for a winding shaft or similar part shall be no larger than is necessary (with sufficient clearance) for the proper operation of the manual station.

6.2.6 Except as noted in Clause 6.2.7, a back box provided for a manual station shall be of a thickness as specified in Subsection 6.3, Cast Metal Enclosures; or Subsection 6.4, Sheet Metal Enclosures.

6.2.7 A manual station need not be furnished with a back box if means for attachment to a standard outlet box are provided and, if while the manual station is mounted on such a back box, the spacings required in Subsection 6.12, Spacings, are provided.

6.2.8 There shall be adequate space within a terminal or wiring compartment to permit the use of a standard conduit bushing on conduit connected to the compartment, if a bushing would be required for proper installation.

6.2.9 A manual station shall have provision for the connection of armoured cable or conduit either to its integral enclosure or to a back box to which it is intended to be attached.

6.2.10 The manual station shall have adequate protection against accidental operation.

6.2.11 A door provided to protect an actuating mechanism or similar part shall be held closed by a latch, catch, spring, or similar device. The method used shall not interfere with the normal operation of the manual station in accordance with the instructions marked upon it. A recess, bevelled surface, or the equivalent may be used to protect the actuating mechanism.

6.2.12 A manual station employing a part intended to be broken during its operation shall be equipped with a suitable breaking device or shall be designed so that injury to the operator shall not occur when operating the manual station. NOTE: The breakable element is intended to give protection against unintentional operation and to be a deterrent against misuse. The visible displacement of the breakable element is accepted apparent breaking.

6.2.13 A door held closed by a break - glass type of latch and intended to be opened during operation of the manual station shall have a handle, tab, spring, or similar part to facilitate opening the door after the glass is broken.

6.2.14 The outside edges, corners, and projections of an enclosure which will be exposed after installation, or projecting operating controls, shall be smooth and rounded to a radius of 2 mm to minimize the possibility of a cut injury or injury by impact.

6.3 CAST METAL ENCLOSURES

6.3.1 The thickness of cast metal for an enclosure shall be as indicated in Table 1, except that cast metal of lesser thickness may be employed if, upon investigation (consideration being given to the shape, size and function of the enclosure), it is found to have adequate mechanical strength. See Subsection 8.17, Mechanical Strength Tests for Enclosures.

6.3.2 Die - cast metal for other than flush back boxes shall comply with one of the alloy specifications given in ANSI/ASTM B86, Standard Specification for Zinc and Zinc - Aluminum (ZA) Foundry and Die Castings.

6.3.3 If threads for the connection of conduit are tapped all the way through a hole in an enclosure wall, or if an equivalent construction is employed, there shall be no fewer than three and one half nor more than five threads in the metal, and the construction shall be such that a standard conduit bushing can be properly attached.

6.3.4 If threads for the connection of conduit are tapped only part of the way through a hole in an enclosure wall, there shall be no fewer than five full threads in the metal and a smooth, well - rounded inlet hole for the conductors, which shall afford protection to the conductors equivalent to that provided by a standard conduit bushing, eyelet, or grommet.

6.3.5 Die-cast metal for other than flush boxes is permitted when it complies with one of the alloy specifications given in ANSI/ASTM B86, Standard Specification for Zinc and Zinc-Aluminum (ZA) Alloy Foundry and Die Castings.

6.3.6 Compliance of a zinc-base alloy die casting with the requirement of Clause 6.3.5 is to be determined by ASTM E27, Standard Method of Spectrographic Analysis of Zinc and Zinc-Alloys by the Solution-Residue Technique.

6.4 SHEET - METAL ENCLOSURES

6.4.1 The thickness of sheet metal employed for the enclosure shall be not less than that indicated in Table 2 except that sheet metal of two sizes lesser thickness may be employed if the surface under consideration is curved, ribbed, or otherwise reinforced, or if the shape, size, or both shape and size of the surface is such that equivalent mechanical strength is provided.

6.4.2 At any point where conduit or metal - clad cable is to be attached, sheet metal shall be of such thickness or shall be so formed or reinforced that it will have a stiffness at least equivalent to that of an uncoated flat steel sheet having a minimum thickness of 1.35 mm.

6.4.3 A plate or plug closure for an unused conduit opening or other hole in the ultimate enclosure shall be not less than 0.69 mm thick if of steel, or 0.81 mm thick if of nonferrous metal, for a hole having a 35 mm maximum diameter.

6.4.4 A closure for a hole larger than 35 mm diameter shall have a thickness equal to that required for the enclosure of the manual station or a standard knockout seal shall be used. Such plates or plugs shall be mechanically secured.

6.4.5 A knockout in a sheet metal enclosure shall be secured but shall be capable of being removed without deformation of the enclosure.

6.4.6 A knockout shall be provided with a flat surrounding surface acceptable for seating of a conduit bushing and shall be located so that installation of a bushing at any knockout likely to be used during installation will not result in spacings between uninsulated live parts and the bushing of less than those indicated under Subsection 6.12, Spacings.

6.4.7 An enclosure intended for recessed mounting shall have no nonfunctional openings on any of the enclosed sides.

6.5 NON - METALLIC ENCLOSURES

6.5.1 An enclosure or parts of an enclosure of nonmetallic material shall have the mechanical strength and be formed so that operating parts will be protected against damage. The mechanical strength of the enclosure shall be at least equivalent to a sheet metal enclosure of the minimum thickness specified in Table 2. See Subsection 8.17, Mechanical Strength Tests for Enclosures, and Subsection 8.18, Polymeric Materials Test.

6.5.2 Among the factors to be taken into consideration when judging the acceptability of a nonmetallic enclosure are the following:

A    The mechanical strength;

B     Resistance to impact;

C     Moisture absorptive properties;

D     Flammability and resistance to ignition from electrical sources;

E     Dielectric strength, insulation resistance, and resistance to arc tracking; and

F     Resistance to distortion and creeping at temperatures to which the material may be subjected under conditions of normal or abnormal usage.

6.5.3 The continuity of the grounding system shall not rely on the integrity of the nonmetallic material.

6.6 ELECTRIC SHOCK

6.6.1 Any part that is exposed only during operator servicing shall not present the risk of electric shock. See Subsection 8.10, Electric Shock Current Test.

6.6.2 The insertion in any socket of any plug - in component used in the manual station shall not result in a risk of electric shock.

6.7 CORROSION PROTECTION

6.7.1 Metal parts, other than a bearing or similar part for which such protection is impracticable, shall be suitably protected against corrosion by enamelling, galvanizing, sherardizing, plating, or other equivalent means. Parts made of stainless steel do not require additional protection against corrosion.

6.7.2 The requirement of Clause 6.7.1 applies to all metal enclosures, and to all springs and other parts upon which intended mechanical operation may depend. Bearing surfaces shall be of materials and construction that reduce the likelihood of binding due to corrosion.

6.7.3 The requirement in Clause 6.7.1 does not apply to minor parts such as washers, screws and bolts, if the failure of such unprotected parts would not be likely to result in a risk of fire, electric shock, or unintentional contact with moving parts that can cause injury to persons or prevent the intended operation of the manual station.

6.7.4 Metal shall not be used in combinations such as to cause galvanic action. Refer to Annex F of CSA C22.2 No 60065, Audio, Video, and Similar Electronic Equipment.

6.7.5 Cabinets and enclosures of corrosion-resistant material may be employed without special corrosion protection.

6.7.6 For outdoor-use, an enclosure of sheet steel less than 3.04 mm in thickness, 3.18 mm or less if zinc coated, shall be galvanized by the hot-dip process after forming and assembly, or shall be made from hot-dipped sheets, or shall be provided with a coating which is at least the equivalent, with respect to corrosion protection, of zinc applied by the hot-dip process.

6.8 FIELD WIRING CONNECTION

6.8.1 General

6.8.1.1 A wiring terminal or lead shall be acceptable for the connection of conductors of at least the size required by CSA C22.1, Canadian Electrical Code, Part I, Safety Standard for Electrical Installations, corresponding to the electrical rating of the unit.

6.8.1.2 Wiring terminals shall be prevented from turning.

6.8.1.3 The terminals to which wiring connections are made shall consist of binding screws with terminal plates having upturned lugs or the equivalent to hold the wires in position. Other terminal connections may be provided if found to be equivalent.

6.8.1.4 Dual terminals or dual leads, or equivalent means to achieve electrical supervision, shall be provided for each incoming and outgoing alarm - initiating - circuit connection.

6.8.1.5 A common dual terminal may be used for connection of both incoming and outgoing wires, provided that the construction of the terminal does not permit an uninsulated section of a single conductor to be looped around the terminal and serve as two separate connections, thereby precluding supervision of the connection in the event that the wire becomes dislodged from under the terminal.

6.8.1.6 A notched clamping plate under a single securing screw, in which separate conductors of an initiating circuit are intended to be inserted under each notch, is acceptable, but this arrangement shall be supplemented by additional marking in the wiring area or on the installation wiring diagram specifying the intended connections to the terminals.

6.8.2 Field Wiring Compartment

6.8.2.1 The field wiring compartment to which connections are to be made shall provide sufficient space to complete all wiring connections specified by the installation wiring diagram without damage to wire insulation or to internal components. There shall be space within the compartment to permit the use of a standard conduit bushing on conduit connected to the compartment when a bushing is required.

6.8.2.2 The device wiring and internal components in the wiring area of a device designed for mounting to an outlet box shall be located or protected so that, they and the field wiring in the outlet box are not forced against sharp edges to prevent damage

6.8.2.3 The wiring terminals of a manual station intended for mounting in an outlet box shall be located or protected such that the wiring in the outlet box is not dislodged or forced against the terminals so as to adversely affect the conductor insulation when mounted as intended.

6.8.3 Terminals and Leads

6.8.3.1 Terminal parts by which connections are made shall ensure reliable connections even under hard usage. For 2.59 mm (No. 10 AWG) and smaller wires, the parts to which wiring connections are made may consist of clamps or binding screws with terminal plates having upturned lugs or the equivalent to hold the wires in position. Other terminal connections may be provided if found to be equivalent.

6.8.3.2 If a wire - binding screw is employed at a wiring terminal, the screw shall be not smaller than No. 8, except that a No. 6 screw may be used for the connections of a 1.63 mm diameter (No. 14 AWG) or smaller conductor. A wire - binding screw shall thread into metal and shall be of nonferrous metal or plated steel.

6.8.3.3 Except as noted in Clause 6.8.3.4, a terminal plate tapped for a wire - binding screw shall be of metal not less than 0.27 mm in thickness for a No. 8 or larger screw, and not less than 0.76 mm in thickness for a No. 6 screw, and shall have no fewer than two full threads in the metal.

6.8.3.4 A terminal plate may have the metal extruded at the tapped hole for the binding screw so as to provide two full threads. Other constructions may be employed if they provide equivalent ruggedness of the terminal plate and thread security of the wire - binding screw.

6.8.3.5 Leads provided for field connections shall be stranded copper bunch tinned, not less than 150 mm long, provided with strain relief, and not smaller than 1.02 mm diameter (No. 18 AWG). Rubber or thermoplastic insulation shall be not less than 0.8 mm thick.

6.8.4 Ground Terminal and Lead

6.8.4.1 In a manual station intended for connection to a source of supply only by means of other than a metal - enclosed wiring system, such as non-metallic-sheathed cable:

A    An equipment ground terminal or lead shall be provided. The size shall be the same as the supply terminal or lead, but in no case smaller than 1.02 mm diameter (No. 18 AWG);

B     A marking shall be provided to indicate the system or systems with which it is intended to be used and;

C     The bonding means shall be acceptably connected to all exposed dead metal parts which are likely to become energized and all dead metal parts within the enclosure that are exposed to contact during servicing and maintenance.

6.8.4.2 The surface of an insulated lead intended solely for the connection of an equipment bonding conductor shall be green, with or without one or more yellow stripes. No other leads visible to the installer, other than grounding conductors, shall be so identified. The bonding means shall be used for no other purpose.

6.8.4.3 A field wiring terminal intended for connection of an equipment bonding conductor shall be plainly identified as per the requirements of CSA C22.2 No. 0.4, Bonding of Electrical Equipment, such as being marked G, GR, Ground, the internationally accepted ground symbol or by a marking on a wiring diagram provided on the appliance. The field - wiring terminal shall be located so that it is unlikely to be removed during servicing of the manual station.

6.8.5 Strain Relief

6.8.5.1 A strain relief means shall be provided for the field supply leads and for all internally connected wires subject to movement during installation, operation, or servicing of the manual station to prevent any mechanical stress from being transmitted to terminals and internal connections.

6.8.5.2 Inward movement of leads provided with a ring - type strain relief or equivalent means shall neither damage internal connections or components nor result in reduction of electrical spacings.

6.8.5.3 Each lead employed for field connections or an internal lead subjected to movement or handling during installation and servicing shall be capable of withstanding for 1 min, a pull of 45 N without any evidence of damage or of transmitting the stress to internal connections.

6.9 INTERNAL WIRING

6.9.1 General

6.9.1.1 The internal wiring of a manual station shall consist of suitably insulated conductors having adequate mechanical strength and current carrying capacity for the service and temperatures to which it may be subjected.

6.9.1.2 The wiring shall be routed away from moving parts and sharp projections, and shall be held in place with clamps, string ties, or the equivalent unless sufficiently rigid to retain its shaped form.

6.9.1.3 Leads or a cable assembly connected to parts mounted on a hinged cover shall be of sufficient length to permit the full opening of the cover without applying stress to the leads or their connections.

6.9.1.4 The leads shall be secured or equivalently arranged to prevent abrasion of insulation and jamming between parts of the enclosure.

6.9.1.5 Stranded conductors clamped under wire - binding screws shall have the individual strands soldered together or equivalently arranged to ensure reliable connections.

6.9.2 Separation of Circuits

6.9.2.1 Internal wiring of circuits that operate at different potentials shall be reliably separated by barriers (see Subsection 6.9.5, Barriers), clamps, routing, or other equivalent means that ensure permanent separation sufficient for the conductors of the circuit having the highest voltage, unless all conductors are provided with insulation that is suitable for the highest potential involved.

6.9.3 Wireways

6.9.3.1 Wireways shall be smooth and entirely free from sharp edges, burrs, fins, moving parts, etc., that might abrade the conductor insulation.

6.9.3.2 Holes in sheet - metal walls through which insulated conductors pass shall be provided with smoothly rounded bushings or shall have smooth, well rounded surfaces upon which the wires may bear to prevent abrasion of the insulation.

6.9.4 Splices

6.9.4.1 All joints and connections shall be mechanically secure and shall provide adequate and reliable electrical contact without strain on connections and terminals.

6.9.4.2 A splice shall be provided with insulation equivalent to that on the wires being joined.

6.9.4.3 A splice shall be located, enclosed, and supported so that it is not subject to damage from flexing, motion, or vibration.

6.9.5 Barriers

6.9.5.1 Barriers used to provide separation between the wiring of different circuits shall be of metal or of suitable insulating material; of adequate mechanical strength if exposed or otherwise likely to be subject to mechanical injury; and reliably held in place.

6.9.5.2 A barrier of insulating material shall be not less than 0.71 mm in thickness and shall be of greater thickness if its deformation can be readily accomplished so as to defeat its purpose.

6.9.5.3 A metal barrier shall have a thickness at least as great as the required thickness of the enclosure metal. See Tables 1 and 2.

6.10 BONDING FOR GROUNDING

6.10.1 All non - current carrying metal parts that are likely to become energized shall be bonded to ground.

6.10.2 Bonding and grounding shall be in accordance with the requirements of CSA C22.2 No. 0.4, Bonding of Electrical Equipment. The bonding means shall be used for no other purpose.

6.10.3 An uninsulated dead metal part of a cabinet, electrical enclosure, capacitor or other electrical components, shall be bonded for grounding if it may be contacted by the user or by service personnel servicing the equipment.

6.10.4 A bonding means shall be an acceptable electrical conductor. If of ferrous metal, it shall be protected against corrosion by painting, plating, or the equivalent. The conductor shall be of acceptable size. A separate bonding conductor shall be installed so that it is protected from mechanical damage.

6.10.5 The bonding shall be by a positive means, such as by clamping, riveting, bolted or screwed connection, brazing, or welding. The bonding connection shall penetrate nonconductive coatings, such as paint. Bonding around a resilient mount shall not depend on the clamping action of rubber or similar material.

6.10.6 A bolted or screwed connection that incorporates a star washer or serrations under the screwhead is acceptable for penetrating nonconductive coatings where required for compliance with Clause 6.10.5.

6.10.7 When the bonding means depends upon screw threads, the use of two or more screws or two full threads of a single screw engaging metal complies with Clause 6.10.5.

6.10.8 A metal-to-metal hinge-bearing member of a door or cover is acceptable as a means for bonding the door or cover for grounding, provided that a multiple bearing-pin type (piano-type) hinge is employed.

6.10.9 The size of a copper or aluminum conductor employed to bond an electrical enclosure or motor frame shall be based on the rating of the branch-circuit overcurrent device by which the appliance will be protected. The size of the conductor shall be in accordance with Table 3.

6.10.10 A conductor, such as a clamp or strap, may be used in place of a separate wire conductor, provided that the minimum cross-sectional conducting area of the bonding means is not less than that of the wire indicated in Table 3.

6.10.11 A splice shall not be employed in a wire conductor used for bonding.

6.11 COMPONENTS

6.11.1 Current - Carrying Parts

6.11.1.1 A current - carrying part shall have adequate mechanical strength and current - carrying capacity for the service, and shall be of metal that is recognized as suitable for the particular application, such as silver, copper, or a copper - base alloy.

6.11.1.2 Bearings, hinges, etc., are not acceptable for carrying current between fixed and moving parts.

6.11.2 Coil Windings

6.11.2.1 The insulation of coil windings in electromagnets shall be moisture resistant.

6.11.2.2 Film - coated wire is not required to be given additional treatment to prevent moisture absorption.

6.11.3 Insulating Material

6.11.3.1 A base for the support of live parts shall be of a strong, non - combustible, moisture - resistant, insulating material such as porcelain, phenolic, or cold - moulded composition, or other material that is recognized as suitable for the support of live parts.

6.11.3.2 Vulcanized fibre may be used for insulating bushings, washers, separators, and barriers, but not for the sole support of live parts if shrinkage, current leakage, or warping of the fibre may introduce a hazard.

6.11.3.3 Polymeric materials may be used for the sole support of uninsulated live parts if found to have acceptable mechanical strength and rigidity, dielectric strength, resistance to heat, flame propagation, arcing, creep, and moisture, and other properties necessary for the application, without displaying a loss of these properties beyond the minimum acceptable level as a result of aging when tested as specified in Subsection 8.18, Polymeric Materials Test.

6.11.3.4 A flat sheet of acceptable insulating material, such as phenolic composition, employed for panel - mounting of parts, shall be not less than 10 mm thick, except that material less than 10 mm thick but not less than 3.2 mm thick may be employed for a panel if the panel is supported or reinforced to provide rigidity not less than that of a 10 mm material.

6.11.3.5 Material less than 3.2 mm thick may be employed for sub-assemblies, such as supports for terminals for internal wiring, resistors, and other components.

6.11.3.6 A base mounted on a metal surface that might be grounded shall be provided with an insulating barrier between the mounting surface and all live parts on the underside of the base that are mechanically prevented from loosening so as to prevent such parts and the ends of replaceable terminal screws from coming in contact with the supporting surface.

6.11.3.7 A countersunk, sealed part shall be covered with a waterproof insulating compound that does not melt at a temperature 15 °C higher than the maximum normal operating temperature of the assembly, and at not less than 65 °C in any case. The depth or thickness of sealing compound shall not be less than 3.2 mm.

6.11.4 Printed Wiring Boards

6.11.4.1 The securing of components to the board shall be made in a positive manner and the spacings between circuits shall be as specified in Subsection 6.12, Spacings.

6.11.4.2 All printed wiring boards shall be securely mounted.

6.11.4.3 The board shall be mounted so that deflection of the board during installation or servicing does not result in damage to the board or in a risk of fire or electric shock.

6.11.5 Switches

6.11.5.1 A switch provided as part of a unit shall have current and voltage ratings not less than those of the circuit that it controls when the manual station is operated under any condition of intended service.

6.11.5.2 If a reset switch is provided it shall be of a self - restoring type.

6.11.6 Mounting of Components

6.11.6.1 All parts of a manual station shall be securely mounted in position and prevented from loosening or turning if such motion may adversely affect the normal performance of the equipment, or may affect the fire and accident hazard incident to operation of the equipment.

6.11.6.2 Uninsulated live parts shall be secured to their supporting surfaces so that they will be prevented from turning or shifting in position if such motion might result in a reduction of spacings to less than those indicated in Subsection 6.12, Spacings. Contact assemblies shall be secured to ensure the continued alignment of contacts.

6.11.6.3 Friction between surfaces is not acceptable as a means to prevent turning, loosening, or shifting of a part as required in Clauses 6.11.6.1and 6.11.6.2, but a suitable lock washer or the equivalent, properly applied, is acceptable.

6.11.6.4 A flush plate, for outlet - box mounting, provided with a manual station or as an integral part thereof shall be of ferrous metal not less than 0.76 mm thick; copper or brass (nonferrous metal) not less than 1.02 mm thick; or non - conductive, non - combustible material at least 2.54 mm thick.

6.11.6.5 A yoke, strap, or mounting ears of a part intended to be mounted on a standard outlet box or similar back box shall be not less than 1.02 mm thick if of ferrous metal. If a non - ferrous metal is used, it shall be of thickness sufficient to provide mechanical strength and rigidity not less than that of 1.02 mm thick steel.

6.11.7 Operating Mechanisms

6.11.7.1 Parts shall be constructed of materials that are suitable for the particular application, and shall be of adequate mechanical strength.

6.11.7.2 An operating mechanism shall be so assembled that it is not adversely affected by any condition of its intended operation and is not impaired by any wiring within the enclosure.

6.11.7.3 Moving parts shall have sufficient clearance at bearing surfaces to prevent binding.

6.11.7.4 Provision shall be made to prevent adjusting screws and similar adjustable parts from loosening under the conditions of actual use.

6.11.7.5 Manually operated parts shall have sufficient strength to withstand the stresses to which they are subject in operation.

6.11.7.6 An electromagnetic component shall be designed to ensure reliable and positive electrical and mechanical performance under all conditions of its intended operation.

6.11.7.7 Interrelated operating parts shall be formed and assembled so that their alignment is maintained.

6.11.8 Capacitors

6.11.8.1 Capacitors shall be rated for the intended application under all environmental conditions to which they may be exposed in service and shall be so constructed that it will not constitute an undue fire hazard.

6.11.8.2 Capacitors shall be suitable for the purpose. There shall be no failure of the capacitors when the manual station is subjected to Subsection 8.8, Temperature Test; and Subsection 8.4, Overload and Endurance. The measured peak voltage across the capacitor shall not exceed the voltage stress level as specified in Subsection 8.5, Component Stress.

6.11.8.3 A paper capacitor shall be impregnated or suitably enclosed to exclude moisture.

6.11.9 Bushings

6.11.9.1 Where a lead or wire harness passes through an opening in a wall, barrier, or enclosing case, there shall be a metal or insulating bushing, or the equivalent, that shall be secured in place and have a smooth rounded surface against which the wire may bear.

6.11.9.2 If the opening is located in a phenolic composition or other equivalent non-conducting material or in metal of thickness greater than 1.07 mm (0.042 inch), a smooth rounded surface having rounded edges is deemed to be the equivalent of a bushing.

6.11.9.3 Ceramic materials and some moulded compositions are permitted for insulating bushings, but separate bushings of wood and of hot-moulded shellac are not permitted.

6.11.9.4 A fibre bushing may be used if:

A    It will not be subjected to a temperature higher than 90 °C (194 °F) under intended operating conditions;

B    The bushing is not less than 1.2 mm (0.47 in) thick; and

C    The fibre will not be exposed to moisture.

6.11.9.5 Ordinary vulcanized fibre may be employed where it will not be subjected to a temperature higher than 90 °C under intended operating conditions if the bushing is not less than 1.2 mm in thickness and if it will not be exposed to moisture.

6.11.9.6 If a soft rubber bushing is employed in a hole in metal, the hole shall be free from sharp edges, burrs, projections, and the like, which could cut into the rubber.

6.11.9.7 An insulating-metal grommet is acceptable in lieu of an insulating bushing, provided that the insulating material used is not less than 0.8 mm in thickness and fills completely the space between the grommet and the metal in which it is mounted.

6.11.10 Semiconductors

6.11.10.1 Semiconductors shall be rated for the intended application under all environmental conditions to which they may be exposed in service. See Section 8, Performance Tests.

6.12 SPACINGS

6.12.1 Except as noted in Clause 6.12.8, the spacings in a manual station shall be not less than those indicated in Table 3.

6.12.2 The values of Table 3 apply to the spacings between any uninsulated live part and an uninsulated live part of opposite polarity, either grounded or ungrounded; the walls and cover of a metal enclosure, including attached metal pieces and fittings for conduit or armoured cable; an uninsulated, grounded, dead metal part other than the enclosure; and an exposed dead metal part that is isolated (insulated).

6.12.3 Greater spacings may be required if the enclosure, because of its size, shape, or the material used, is not sufficiently rigid to warrant the minimum spacings.

6.12.4 If a short circuit between uninsulated live parts of the same polarity would adversely affect the normal signalling operation of the manual station or result in a false alarm signal, the spacing between such parts shall be not less than that required between parts of opposite polarity.

6.12.5 Except as indicated in Clause 6.12.6, a barrier or liner of insulating material that is used to provide spacings shall be of material suitable for the particular application and shall be not less than 0.71 mm in thickness.

6.12.6 A barrier or liner that is used in conjunction with no less than half of the required spacing through air may be less than 0.71 mm but shall be not less than 0.33 mm in thickness, provided that the barrier or liner is: of a good quality suitable insulating material that is resistant to moisture; of adequate mechanical strength if exposed or otherwise subject to mechanical injury; reliably held in place; and so located that it will not be adversely affected by operation of the manual station in service, particularly arcing.

6.12.7 Film - coated wire is considered to be a bare current-carrying part in determining compliance of the manual station with the spacing requirements, but is acceptable as turn-to-turn insulation in coils.