The simplest electrical cable may just be a metal conductor – these cables are used as overhead line wires manufactured without any insulating material around the conductor other than the air that surrounds the conductor. Overhead cables such as those used in the rail industry, require?practical considerations to ensure that the cable is isolated from any means of accidentally grounding the electrical conductor (grounding the cable would see the current pass through it, electrocuting anyone in contact). Commonly used Rail OHL including Hornet and Cockroach have PVC insulated variations. Cables used either at ground level, within reasonable reach, or underground need to be effectively insulated to both maintain current flow through the cable and to be safe for users.
The amount of current which can effectively flow through the electrical cable will be determined by a combination of factors:
the cross-sectional area of the conductor
the resistance of the conductor material
the insulation material
the installation method or environment.
The effect of resistance to current flow is the heating of the conductor and the surrounding insulation layers. Over-heating has the potential to cause failure of the insulation material resulting in current short circuiting, electric shock, or fire.
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