• Robert Brown

Electrical related vehicle fire!!!

Dr Brown was involved in case heard at Glasgow Sheriff Court last week concerneing a

alleged to have ignited due to an electrical fault.

Electrical fires can manifest thorugh two (2) fundamental electrical phenomena.

• Joule Heating

• Electrical arcing

Joule heating

Joule heating, also known as Ohmic heating and resistive heating, is the process by which the passage of an electric current through an electrical conductor (such a cable or wire) produces heat.

Heat generation and dissipation from the cable/wire is proportional to

• The electrical resistance of the length of cable/ wire.

• The electrical current flowing through the cable/ wire.

So if say a cable becomes damaged in some way that the electrical resistance increases, heat generation within and dissipation from the cable will increase and in time if left unchecked the temperature of the cable will attain a point where the outer insulating plastic coating of the cable will disintegrate and ignite into flame.

Of course if heat generation continues, the metallic medium of the cable will transpose from a solid to a liquefied state, which then due to gravitational and surface tension forces will migrate and separate forming air gaps between which electrical arcing will manifest.

Electrical arcing

An electric arc, or arc discharge, is an electrical breakdown of a gas that produces an ongoing electrical discharge. The current through a normally nonconductive medium such as air produces an ‘arc plasma’.

An electrical arc is characterised by its highly intense white/blue light and extremely high temperature.

Electrical arcing will manifest wherever there are two electrodes between which a high energy, electrical charge exists, sufficient to ionise the air between. In simple words the air becomes a conductor of electricity.

So, say an electrical wire comes adrift from its termination point and the wire is charged with a sufficient voltage, an electrical arc will, most likely, manifest between the parting wire ends.

For further information or help, ...



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