15A Presence of Water (AD) or High Humidity (AB)*
(1) Construction of equipment
(2) Conductors and enclosures of wiring installations (3) Switches and socket outlets
15B Ambient Temperature (AA) (1) General
(2) Electrical insulations (3) Conductors and cables
(4) Enclosures of wiring installations (5) External heat sources
15C Presence of Corrosive or Polluting Substance (AF) 15D Installation Exposed to Fire or Explosion
(1) General
(2) Electrical equipment selection (3) Wiring systems
15E Impact (AG) 15F Vibration (AH)
15G Other Mechanical Stresses (AJ)
* For codes of external influences, table 15(3) refers.
Code 15 ADVERSE CONDITIONS INSTALLATION
15A Presence of Water (AD) or High Humidity (AB) (1) Construction of equipment
(a) A wiring system should be selected and erected so that no damage is caused by high humidity, high condensation or ingress of water during installation, use and maintenance.
(b) Where water may collect or condensation may form in a wiring system, provision should be made for its harmless escape through suitably located drainage points.
(c) Where a wiring system may be subjected to waves (AD6), protection against mechanical damage should be afforded by one or more of the methods given in Codes 15E, 15F and 15G.
(2) Conductors and enclosures of wiring installations
(a) Copperclad aluminium conductors should not be used.
(b) All exposed conductors and insulations at terminations and joints of cables that are insulated with impregnated paper should be suitably sealed against ingress of moisture.
(c) Every joint in a cable should be suitably insulated and protected against the effect of moisture or water.
(d ) Overall PVC covering should be provided for mineral insulated cable.
(e) The ends of mineral insulated cables should be suitably sealed with purposely designed terminations and sealing material, having adequate insulating and moisture proofing properties throughout the range of temperatures to which they may be subjected in service. The mineral insulation of the cables should be thoroughly dried before the sealing material is applied.
( f ) Every entry to finished ducts, ducting or trunking should be placed so as to prevent the ingress of water, or be protected against such ingress.
(g) All metal sheath and armour of cables, metal conduits, ducts, ductings, trunkings, clips and their fixings, should be of corrosion resisting material or finish and should not be placed in direct contact with other dissimilar metals which they are liable to set up electrolytic action.
In particular, contact between bare aluminium sheaths or aluminium conduits and any parts made of brass or other metal having a high copper content should be avoided in damp situation unless the parts are suitably plated.
(h) In damp situations, enclosures for cores of sheathed cables from which the sheath has been removed and for non-sheathed cables at terminations of conduit, duct, ducting or trunking systems, should be damp proof and corrosion resistant.
(i ) Metallic sheaths, conduits etc. in installations underwater or likely to be underwater should not be relied upon as the only protective conductor and a separate copper protective conductor should be used.
(3) Switches and socket outlets
(a) Switches having watertight enclosures with minimum IP54 or equivalent are acceptable for an installation exposed to weather.
(b) Socket outlets complying with IEC 60309-2 or equivalent and provided with a push-on cap and cap retaining ring or a screw-on cap with rubber gasket are acceptable for an installation exposed to weather. The socket outlets should also have a degree of protection of at least IPX4 or equivalent.
15B Ambient Temperature (AA) (1) General
(a) A wiring system should be selected and erected so as to be suitable for the highest and lowest local ambient temperature likely to be encountered.
(b) The components of a wiring system, including cables and wiring enclosures should be installed or handled only at temperatures within the limits stated in the relevant product specification or as recommended by the manufacturer.
(2) Electrical insulations
The maximum permissible operating temperature for various classes of insulation complying with IEC 60085 are given in Table 15(1).
(3) Conductors and cables
(a) The type and current carrying capacity of every conductor, cable and flexible cord, termination and joint should be selected so as to be suitable for the highest operating temperature likely to occur in normal service, account being taken of any transfer of heat from any accessory, appliance or luminaire to which the conductor, cable or flexible cord is connected.
(b) The maximum operating and ambient temperatures, in general, for various types of cable insulations are given in Table 15(2).
(c) Where cables are to be connected to bare conductors or busbars, it should be verified that their type of insulation and/or sheath is suitable for the maximum operating temperature of the bare conductors or busbars.
(4) Enclosures of wiring installations
(a) The enclosures of wiring installations for conductors and cables should be selected and installed so that they are suitable for the extremes of ambient temperature to which they are likely to be exposed in normal service.
(b) In every vertical channel, duct, ducting or trunking installations containing conductors or cables, internal barriers should be provided between floors or at intervals of 5 m whichever is the less so as to prevent the air at the top of the channel, duct, ducting or trunking from attaining an excessively high temperature.
(5) External heat sources
(a) To avoid the effects of heat from external sources including solar gain, one or more of the following methods, or an equally effective method, should be used to protect the wiring system:
(i) shielding;
(ii) placing sufficiently far from the source of heat;
(iii) selecting a system with due regard for the additional temperature rise which may occur;
(iv) local reinforcement or substitution of insulating material.
(b) Parts of a cable or flexible cord within an accessory, appliance or luminaire should be suitable for the temperatures likely to be encountered, as determined in accordance with Code 15B(1)(a), or should be provided with additional insulation suitable for those temperatures.
15C Presence of Corrosive or Polluting Substance (AF)
(a) Where the presence of corrosive or polluting substances is likely to give rise to corrosion or deterioration, parts of the wiring system likely to be affected should be suitably protected or manufactured from materials resistant to such substances.
(b) Metals liable to initiate electrolytic action should not be placed in contact with each other.
(c) Suitable precautions against corrosion should be taken for metalwork and metallic parts of wiring systems that are liable to chemical or electrolytic attack by materials of a structure with which they may come in contact. Materials likely to cause such attack include:
(i) materials containing magnesium chloride which are used in the construction of floors and dadoes;
(ii) plaster undercoats contaminated with corrosive salts;
(iii) lime, cement and plaster, for example on unpainted walls;
(iv) oak and other acidic woods;
(v) dissimilar metals liable to set up electrolytic action.
Application of suitable coatings before erection, or prevention of contact by separation with plastics, are recognised as a suitable precaution against corrosion.
(d ) Non-metallic materials used in wiring systems should not be placed in contact with materials likely to cause chemical deterioration of the wiring systems. Such materials should either be installed where they will not be exposed to contact with oil, creosote, and similar hydrocarbons, or be of a type designed to withstand such exposure.
(e) Overall PVC covering should be provided for mineral-insulated cables that are exposed to risk of corrosion.
( f ) In onerous dust conditions, enclosures of the wiring installations should have a degree of protection such that dust cannot enter in sufficient quantity to interfere with operation of the equipment.
Enclosures built to IP5X or equivalent are considered acceptable.
15D Installation Exposed to Fire or Explosion (1) General
(a) Electrical equipment and wiring of electrical installations exposed to potentially explosive atmospheres should be constructed and protected to the requirements specified for hazardous areas to IEC 60079 or BS5501 or equivalent.
(b) Electrical equipment and wiring of electrical installations in buildings and premises for the storage, manufacture or packing of dangerous goods in Categories 1 to 10 must comply with the provisions of Dangerous Goods (General) Regulations (Cap. 295).
(c) Electrical equipment and wiring of electrical installations in building and premises for Categories 2 and 5 Dangerous Goods including those in building and premises for liquid petroleum gas storage and for petrol filling stations should, in addition to subparagraphs (a) and (b) above, comply with the requirements specified for hazardous areas in the Electrical Safety Code Part 1 and 15 of the Energy Institute/Institute of Petroleum Model Code of Safe Practice for the Petroleum Industry or equivalent.
(d ) Electrical equipment and wiring of electrical installations in mines should comply with the Mining Ordinance and Mines (Safety) Regulations (Cap. 285), and should be constructed and protected to relevant recognised standards.
(2) Electrical equipment selection
(a) Type of protection of electrical equipment for achievement of safety should be in accordance to zone of risk listed in Table 15(4).
(b) The maximum surface temperature of the T class of an electrical equipment should not exceed the ignition temperature of the gases or vapours involved. Relationship between T class and maximum surface temperature is shown in Table 15(5).
(c) Electrical equipment with the appropriate apparatus group should be used.
Group I: Electrical apparatus for mines susceptible to firedamp.
Group II: Electrical apparatus for places with a potentially explosive atmosphere, other than mines susceptible to firedamp.
(3) Wiring systems
The type of wiring that may be used for installation in hazardous areas, and the requirements for permitted types of cable and their accessories dealing with individual types of protection should comply with the recommendations laid down in IEC 60079 or equivalent. All cables, conduit and their accessories should be manufactured to appropriate recognised standards.
15E Impact (AG)
(a) A wiring system should be selected and erected so as to minimise mechanical damage.
(b) In a fixed installation where an impact of medium severity (AG2) or high severity (AG3) can occur, protection should be afforded by:
(i) the mechanical characteristics of the wiring system, or (ii) the location selected, or
(iii) the provision of additional local or general mechanical protection, or by any combination of the above.
(c) Except where installed in a conduit or duct which provides equivalent mechanical protection, a cable buried in ground should be of a construction incorporating an armour or metal sheath or both, or be of insulated concentric construction. Such cable should be marked by cable
covers or a suitable marking tape or by suitable identification of the conduit or duct and be buried at a sufficient depth to avoid being damaged by any disturbance of the ground reasonably likely to occur.
(d ) A wiring system buried in a floor should be sufficiently protected to prevent damage caused by the intended use of the floor.
(e) Where a cable is installed under a floor or above a ceiling it should be run in such a position that it is not liable to be damaged by contact with the floor or the ceiling or their fixings. Cable should incorporate an earthed metallic sheath suitable for use as a protective conductor or should be protected by enclosure in earthed steel conduit securely supported, or by equivalent mechanical protection sufficient to prevent penetration of the cable by nails, screws, and the like.
( f ) Where a cable is to be concealed within a wall or partition, the concealed cable should incorporate an earthed metallic covering which complies with the requirements of this CoP for a protective conductor of the circuit concerned, or should be enclosed in conduit, trunking or ducting satisfying the requirements of this CoP for a protective conductor, or by mechanical protection sufficient to prevent penetration of the cable by nails, screws and the like. In case of a concealed bonding conductor, the conductor should be installed in accordance with the above requirements for a cable, or be installed within 150 mm of the top of the wall or partition or within 150 mm of angle formed by two adjoining walls or partitions in a straight run, either horizontally or vertically to the point or accessory.
(g) For where PVC concealed conduit system is applied, all conduits installed and concealed inside floor slab, wall or partition for cable wiring shall have concrete, cement or plaster cover of thickness not less than 30 mm (or 25 mm for short PVC concealed conduit of length less than 150 mm that is installed within 150 mm of the top of the wall/partition or within 150 mm of an angle formed by two adjoining walls/partitions) to prevent penetration of the cables inside conduits by nails, screws and the like.
15F Vibration (AH)
A wiring system supported by, or fixed to a structure or equipment subject to vibration of medium severity (AH2) or high severity (AH3) should be suitable for the conditions and in particular shall employ cables with fixings and connections suitable for such a situation.
15G Other Mechanical Stresses (AJ)
(a) A wiring system should be selected and erected so as to minimise during installation, use and maintenance, damage to the sheath and insulation of cables and insulated conductors and their terminations.
(b) There should be adequate means of access for drawing cables in or out and, if buried in the structure, a conduit or cable ducting system for each circuit should be completely erected before cables are drawn in.
(c) The radius of every bend in a wiring system should be such that conductors and cables shall not suffer damage.
(d ) Where a conductor or a cable is not continuously supported it should be supported by suitable means at appropriate intervals in such a manner that the conductor or cable does not suffer damage by its own weight.
(e) Every cable or conductor used as fixed wiring should be supported in such a way that it is not exposed to undue mechanical strain and so that there is no appreciable mechanical strain on the terminations of the conductors, account being taken of mechanical strain imposed by the supported weight of the cable or conductor itself.
( f ) A flexible wiring system should be installed so that excessive tensile and torsional stresses to the conductors and connections are avoided.
Table 15(1)
Maximum Permissible Operating Temperature of Various Classes of Insulation to IEC 60085
Note: Temperatures over 250°C should be increased by 25°C intervals and classes designated accordingly.
Class Y A E B F H 200 220 250
Temperature °C 90 105 120 130 155 180 200 220 250
Table 15(2)
Maximum Permissible Operating and
Ambient Temperatures of Some Common Cable Insulations
Notes: (1) Applicable only to cables of 600/1000V voltage grade.
(2) For mineral insulated cables that are sheathed with PVC, the values for general purpose PVC are applicable. Otherwise, the values shown for mineral insulated cables relate only to terminations; elsewhere the temperature of the cable should not exceed 250°C.
(3) XLPE means cross-linked polyethylene.
Maximum Permissible Maximum Permissible Conductor Operating Ambient Temperature Type of Insulation Temperature (°C) (°C)
60°C rubber 60 55
General purpose PVC 70 65
Impregnated Paper
(note 1) 80 75
85°C rubber 85 80
Mineral-insulated
(a) 70°C sheath 70 65
(b) 105°C sheath 105 95
(note 2)
Thermosetting (XLPE) 90 85
(note 3)
150°C rubber 150 145
Glass fibre with 185°C 185 175
varnish
Table 15(3)
Table 15(4)
Selection of Electrical Equipment and Systems according to Zone of Risk
NOTES:
Zone 0 Zone in which an explosive atmosphere is continuously present or present for long periods
Zone 1 Zone in which an explosive atmosphere is likely to occur in normal operation
Zone 2Zone in which an explosive atmosphere is not likely to occur in normal operation, and if it occurs it will exist only for a short time.
Type of Protection Zone in which the protection may be used
‘ia’ intrinsically-safe apparatus or system
‘s’ special protection (specifically certified for used 0, 1, 2 in Zone 0)
‘d’ flammable enclosure
‘ib’ intrinsically-safe apparatus or system
‘p’ pressurization, continuous dilution and 1, 2 pressurized rooms
‘e’ increased safety
‘s’ special protection
‘m’ encapsulation
‘N’ type of protection N
‘o’ oil-immersion 2
‘q’ sand filling
Table 15(5)
Relationship between T Class and Maximum Surface Temperature
T Class Maximum Surface Temperature (°C)
T1 450
T2300
T3 200
T4 135
T5 100
T6 85