An electrical cable comprises two or more wires running side by side and bonded, twisted, or braided together to form a single assembly, the ends of which can be connected to two devices, enabling the transfer of electrical signals from one device to the other.
Cables are used for a wide range of purposes, and each must be tailored for that purpose. Cables are used extensively in electronic devices for power and signal circuits.
Generally Cable should comply with BS-5308, Part -1 (Instrumentation cables. Specification for polyethylene insulated cables).
The Important thing to take care while selecting or preparing specification are as below
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No of Pairs/Traid or Core
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Cable rating
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Number of Twists
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Conductor Size/Type
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Insulation
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Color Code
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Screen/Shield Material Type
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Overall/Individual Scree or Both
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Overlapping Of Screen
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Inner Sheath and Outer Sheath material/Color: Anti vermine(rats or rodent cable)
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Armouring required or note:- Armouring generally required for burried cables
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Oil/Sun/Heat resistance
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Cable halogen Content requirement needs to be verified:- generally PVC cables have Halogen content which is specified to be low or zero when inside.
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Test like Flame retardant,Fire resistant, Test for Insulation integrity, Voltage Test
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Parameter which need to be confirmed are:
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Conductor resistance
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Maximum Drain Wire Resistance including shield
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Insulation Resistance of completed cable
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Maximum Mutual Capacitance of the pairs or adjacent cores
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Maximum capacitance between core or screen
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Maximum L/R ratio for adjacent cores
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Oxygen index
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Minimum installation temperature etc
IEC 60228 is on conductors of insulated cables. Among other things, it defines a set of standard wire cross-sectional areas
International standard wire sizes (IEC 60228)
0.5 mm2 0.75 mm2 1 mm2 1.5 mm2 2.5 mm2 4 mm2
6 mm2 10 mm2 16 mm2 25 mm2 35 mm2 50 mm2
70 mm2 95 mm2 120 mm2 150 mm2 185 mm2 240 mm2
300 mm2 400 mm2 500 mm2 630 mm2 800 mm2 1000 mm2
Class
This refers to the flexibility of a conductor
• Class 1: Solid conductor
• Class 2: Stranded conductor intended for fixed installation
• Class 5: Flexible conductor
• Class 6: Very Flexible conductor
Size
The nominal(see below) cross-sectional area for standard conductors including the following:
• Class 2: Minimum number of strands required to make particular conductor size
• Class 5&6: Maximum diameter of any component strand of the conductor
Resistance
The required maximum resistance (in ohms/km)of each conductor size, class and type (both plain copper and metal coated)
Fire resista nt Cables
Fire Resistant cable shall be as per IEC60331 ( Fire resistant cables are required to capable of operating when exposed to a water spray during fire and shall also comply to BS 6387)
Flame retardan t Cable are as per IEC60332
As per ASTM D2863
Oxygen index: The oxygen index describes the minimum concentration of oxygen,expressed as volume percentage, in a mixture of oxygen and nitrogen that will just support combustion of a material / plastic / compound initially at room temperature under specified test conditions
LOI ≤ 23 combustible
24…28 conditional flame retardant
29…35 flame retardant
≥ 36 „extra“ flame retardant
Flammability Temperature:- The flammability temperature (FT) is the temperature at which combustion of a material / plastic / compound is just supported in air under specified test conditions.
As per IEC 60754-1
Halogen acid gas contains mainly following elements: fluorine, chlorine, bromine or iodine .
• Determination of the amount of halogen acid evolved during the combustion of each combustible material of a cable.
• For materials, which contain less than 5 mg/g (0,5 %) of halogen acid, the test procedure acc. to IEC 60754-2 is recommended.