Current Carrying Capacity of Cables

Current Carrying Capacity of Cables Points : Current Carrying Capacity of Cables, Determination of Total Load, Determination of Number of Sub-Circuits, Determination of Rating Of Main Switch And Distribution Board, Determination of Size of Conductor, The current carrying capacity of any conductor depends directly on its cross-sectional area and inversely on its resistivity. Ambient temperature and shape of together become of reduced capacity. The type of insulation also limits the current strength of a cable. So, selection of a cable for particular job is not simple. Tables of cables help in selecting cables size.

The current carrying capacity of a cable depends on its conducting material’. A25 mm dia bare copper and a 25mm dia hare aluminum have capacities of 940 A and 710 A respectively.

The current rating depends on the shape of the conductor also. A flat bar (25mm x 4mm) has larger surface area than a circular bar 11.3 mm dia) have the same length and cross-section, and can hence dissipate heat more readily and carry a larger working current.

Meaning of Wire and Cables

Meaning of Wire and Cables Points : Meaning of Wire and Cables Any conductor, which is made of conducting material, uniform in diameter and circular in cross-section, is called wire”. A length of a single insulated conductor (solid or stranded) is called “cable”.

Parts of Cable

Parts of Cable Points : Parts of Electric Cable Wires used in electrical circuits are of many types but all consist of the following main parts:
(a) Conductor
(b) Insulation
(c) Mechanical protection

Classification of Cables

Classification of Cables Points : classification of electric cables, v.i.r. vulcanized insulated rubber cables, .t.s or t.r.s (cabtyre sheathed) or (tough rubber sheathed) cables, poly vinyl chloride (p.v.c) insulated cables, lead sheathed cables, flexible cables and cord, weather - proof cables, properties of insulation, according to the number of cores, advantages of stranded conductors over solid conductors, The cable employed for internal wiring of buildings may be divided into different groups according to:
(i) Type of insulation used
(ii) Number of cores used
(iii) Voltage grading and
(iv) Conductor used (i) ACCORDING TO INSULATION The following cables are used for different types of wiring installation.
(I). V.I.R (Vulcanized Insulation Rubber) Cable
(ii) C.T.S (Cabtyre sheathed) Cable or T.R.S (Tough Rubber Sheathed) Cable.
(iii) P.V.C (Poly vinyl Chloride) Cable.
(iv) Lead sheathed cable.
(v) Flexible Cable.
(vi) Whether Proof Cables.