IEC 62420 pdf download – Concentric lay stranded overhead electrical conductors containing one or more gap(s)
5.3Surface
The surface of the conductor shall be free from all imperfections visible to the unaided eye(normal corrective lenses accepted), such as nicks，indentations,etc.，not consistent withgood commercial practice.
5.4Stranding
5.4.1 General
All wires of the conductor shall be concentrically stranded.Before stranding，aluminium andcore wires shall have approximately uniform temperature.
Adjacent wire layers shall be stranded with reverse lay directions.The direction of lay of theexternal layer shall be right-hand except when specifically indicated in the purchase order.
5.4.2Lay ratio for core wires
The lay ratios for the zinc-coated (galvanised) steel or aluminium-clad wire layers shall be asfollows:
a) the lay ratio for the six-wire layer of the core shall be not less than 16 nor more than 26;b) the lay ratio for subsequent core layers shall be not less than 14 nor more than 22.Thelay ratio of subsequent layer(s) shall be not greater than the lay ratio of the core layer
immediately beneath it.
All core wires shall lie naturally in their position in the stranded core,and where the core iscut, the wire ends shall remain in position or be readily replaced by hand and then remainapproximately in position.
5.4.3Lay ratio for aluminium layer(s)
The lay ratios for the aluminium layer(s) shall be as follows:
a) the lay ratio for the outside layer of aluminium wires shall be not less than 10 nor morethan 14;
b) the lay ratios for the inner layers of aluminium wires shall be not less than 10 nor morethan 16;
c) the lay ratio of any aluminium layer shal be not greater than the lay ratio of the aluminium
layer immediately beneath it.
Aluminium wires composing the outside layer of the conductor shall lie naturally in theirposition，and where the conductor is cut, they shall remain in position or be readily replacedby hand and then remain approximately in position.
5.4.4Joints
There shall be no joints of any kind made in the core wire or wires during stranding.
There shall be no joints in the finished aluminium wire prior to stranding.
During stranding，no aluminium wire welds shall be made for the purpose of achieving therequired conductor length.
Joints are permitted in aluminium wires unavoidably broken during stranding，provided suchbreaks are not associated with either inherently defective wire or with the use of short lengths of aluminium wires.Joints shall conform to the geometry of original wire,i.e. joints shall bedressed smoothly with a shape equal to that of the parent wires and shall not be kinked.
Joints in aluminium wires shall not exceed those specified in Table 2.These joints shall notbe closer than 15 m from a joint in the same wire or in any other aluminium wire of thecompleted conductor.
Joints shall be made by electric butt welding, electric butt cold upset welding or cold pressurewelding (see Note 1) and other approved methods. These joints shall be made in accordancewith good commercial practice. The first type of joints shall be electrically annealed forapproximately 250 mm on both sides of the weld.
While the joints specified in this clause are not required to meet the requirements of unjointedwires (see Note 2), they shall withstand a stress of not less than 75 MPa for annealed electricbutt welded joints and not less than 130 MPa for cold pressure and electric butt cold upsetwelded joints. The manufacturer shall demonstrate that the proposed welding method iscapable of meeting the specified strength requirements.
NOTE 1 lt is a practice in some countries to require the annealing of cold pressure joints made in A2 or A3material.
NOTE 2 The behaviour of properly spaced wire joints in stranded conductors is related to both tensile strengthand elongation。Becau5e of higherelongation properties，the lower strength annealed electric butt welded jointgives a similar overall performance to that of a cold pressure or an electric butt cold upset welded joint.
5.4.5Linear mass
The masses given in the Table E.1 of Annex E have been calculated for each size andstranding of conductor using densities for the aluminium，aluminium-clad and zinc-coatedsteel wires as given in the standards listed in Clause 2, the stranding increments given inTable 3, and the cross-sectional areas for aluminium and core wires based on their theoreticalunrounded values.
The increments in per cent, for mass due to stranding, based on the mean lay ratios given in5.4.2 and 5.4.3，shall be taken as given in Table 3. if greater accuracy is desired, actual layfactors shall be used.
Whenever a conductor is to be greased, the nominal mass of grease shall be calculatedaccording to the method given in Annex c.
5.4.6Conductor strength
The rated tensile strength at room temperature of composite conductors shall be the sum ofthe tensile strength of the aluminium portion plus the strength of the core corresponding to anelongation compatible with that of aluminium at rupture load.For the purpose of specificationand practicability,the strength of steel and aluminium-clad steel is conservatively establishedas the stress corresponding to 1 % elongation in a 250 mm gauge length.
The tensile strength of any single wire is the product of its nominal area and the appropriateminimum stress given in the standards listed in Clause 2.
6Tests
6.1classification of tests
Type tests are intended to verify the main characteristics of a conductor which depend mainlyon its design.They are carried out once for a new design or manufacturing process ofconductor and then subsequently repeated only when the design or manufacturing process ischanged.
IEC 62420 pdf download – Concentric lay stranded overhead electrical conductors containing one or more gap(s)
