IEC 60364-4-42:2010 pdf – Low-voltage electrical installations – Part 4-42: Protection for safety -Protection against thermal effects.
421.2 Where fixed equipment may attain surface temperatures which could cause a fire hazard to adjacent materials, the equipment shall either
• be mounted on or within materials that will withstand such temperatures and are of low thermal conductance, or
• be screened from elements of building construction by materials which will withstand such temperatures and are of low thermal conductance, or
• be mounted so as to allow safe dissipation of heat at a sufficient distance from any material on which such temperatures could have deleterious thermal effects, any means of support being of low thermal conductance.
421.3 Where arcs or sparks may be emitted by permanently connected equipment In normal service, the equipment shall either
• be totally enclosed in arc-resistant material, or
• be screened by arc-resistant material from materials on which the emission could have harmful effects, or
• be mounted so as to allow safe extinction of the emissions at a sufficient distance from material upon which the emissions could have harmful effects.
Arc-resistant material used for this protective measure shall be non-ignitable, of low thermal conductivity, and of adequate thickness to provide mechanical stability.
NOTE For example, a sheet made 01 libreglass silicone of 20 mm thickness may be considered as atc-resislant
421.4 Fixed equipment causing a concentration of heat shall be at a sufficient distance from any fixed object or building element so that the object or element, in normal conditions, is not subjected to a dangerous temperature. For example, a temperature in excess of its ignition temperature.
NOTE Any information from the ,nanulacturer of the equipment should be taken into account.
421.5 Where electrical equipment in a single location contains flammable liquid in significant quantity, adequate precautions shall be taken to prevent the spread of liquid, flame and the products of combustion.
NOTE I Examples of such precautions incfuda
• a Ienton pt to coHect any leakage of liquid and ensure exhnction ai the event of lire;
• instalation of th. equipment in a chamber 01 adequale lire resistance and the provision ol sills or other means of Preventing llqud spreading to other paris of th building, such a chamber being ventilated solely to the .itrmei .tmosph,re
NOTE 2 The geii•rally accepted lower limit br a significant quantity is 25 I.
NOTE 3 For quantities less than 25 I, it is sufficient to take precautions to prevent th, escape 01 liquid.
NOTE 4 Products of combustion of liquid are considered to be flame, smok. and gasP
NOTE S it is desirable to switch off the supply at the onset ot a hr..
421.6 The materials of enclosures installed around electrical equipment during erection shall
withstand the highest temperature likely to be produced by the electrical equipment.
Combustible materials are not suitable for the construction of these enclosures unless preventive measures against ignition are taken, such as covering with non-combustible or not readily combustible material of low thermal conductivity.
422 Precautions where particular risks of fire exist
422.1 General
422.1.1 Electrical equipment shall be restricted to that necessary for the use of these locations, except wiring systems according to 4223.5.
422.1.2 Electrical equipment shall be so selected and erected that its temperature in normal use and foreseeable temperature rise during a fault cannot cause a fire.
These arrangements may be effected by the construction of equipment or its conditions of
Special measures are not necessary where the temperature of surfaces is unlikely to cause
Ignition of nearby substances.
422.1.3 Thermal cut-out devices shall have manual resetting only.
422.2 CondItions of evacuation in an emergency
Condition BD2: Low density occupation, difficult conditions of evacuation
BD3: High density occupation, easy conditions of evacuation
BD4: High density occupation, difficult conditions of evacuation
(according to Table 51A of IEC 60364-5-51:2005).
NOTE Aulhonb*s r.pon.bI. fyi buiIdin construc.hoii, publ.c gatherings, tire prevention. dc. may ipecify which 80 condItion Is apphcab4e.
422.2.1 In Conditions BD2. BD3 and BD4, wiring systems shall not encroach on escape routes unless the wiring In the wiring system Is provided With sheaths or enclosures, provided by the cable management system itself or by other means.
Wiring systems encroaching on escape routes shall not be within arm’s reach unless they are provided with protection against mechanical damage likely to occur during an evacuation.
Wiring systems in escape routes shall be as short as practicable and shall be non-flame propagating.