IEC TR 61916:2009 pdf download – Electrical accessories — Harmonization of general rules
5.2 Requirements
5.2.1 Connections, electrical or mechanical, using screws and nuts, shall withstand the mechanical stresses occurring in normal use. Screws and nuts which transmit contact pressure shall be of metal and shall be in engagement with a metal thread. Screws and nuts which are operated when mounting an accessory during installation, and/or which are likely to be operated during the life of the accessory, shall be in engagement with a metal thread. Screws for connecting external conductors shall not be tapping screws. Screws and nuts operated when mounting the accessory during installation, and/or which are likely to be operated during the life of the accessory, shall not be of the thread cutting type.
NOTE 1 Screws and nuts which are operated when mounting the accessory include screws for fixing cover of cover plates, etc., but not connecting means for screwed conduits and screws for fixing the base of the accessory. Compliance is checked by inspection and by the test of 5.3.
NOTE 2 Attention is drawn to the fact that screwed connections also have to comply with the requirements applicable to the accessory.
5.2.2 For screws in engagement with a thread of insulating material and screws of insulating material, which are used for the installation of the accessory and/or which are likely to be operated during the life of the accessory, correct introduction of the screw into the screw hole or nut shall be ensured. Screws of insulating materials shall not be used in cases when the replacement with metal screws could impair the insulation of the accessory. Compliance is checked by inspection and by manual test.
NOTE The requirements with regard to correct introduction are met if introduction of the screw in a slanting manner is prevented, for example by guiding the screw by the part to be fixed, by a recess in the female thread or by the use of a screw with the leading thread removed.
5.2.3 Screws and rivets, intended to be used for electrical connections and screws and rivets intended to be used for mechanical connection, shall be locked against loosening or turning. Compliance is checked by inspection and manual test. NOTE Spring washers may provide satisfactory locking. For rivets, a non-circular shank or an appropriate notch may be sufficient. Sealing compound which softens on heating provides satisfactory locking only for screw connections not subjected to torsion in normal use.
5.2.4 Electrical connections shall be so designed that contact pressure is not transmitted through insulating material other than ceramic, pure mica or other material with characteristics no less suitable, unless there is sufficient resiliency in the metallic parts to compensate for any possible shrinkage or yielding of the insulating material. Compliance is checked by inspection. NOTE The suitability of the material is considered as regards the stability of the dimensions.
5.2.5 Current-carrying parts, including those of terminals (also earthing terminals), shall be of a metal having, under the conditions occurring in the equipment, mechanical strength, electrical conductivity and resistance to corrosion adequate for their intended use. Compliance is checked by inspection and, if necessary, by chemical analysis.IEC TR 61916:2009 pdf download
