Page 124 - 6848

of motors and, in some cases, severe heating may occur without the fuses being
activated.
Loose cable connections are one of the most common causes of overheating
and may be readily detected (as well as overloaded cables) by a thermal imaging

survey (a technique which indicates the presence of hot spots). The bunching of
cables together can also cause excessive heat to be developed within the inner cable
leading to a fire risk. This can happen with cable extension reels, which have only
been partially unwound, used for high-energy appliances like an electric heater.
Ventilation is necessary to maintain safe temperatures in most electrical
equipment and overheating is liable to occur if ventilation is in any way obstructed
or reduced. All electric equipment must be kept free of any obstructions that restrict
the free supply of air to the equipment and, in particular, to the ventilation apertures.
Most electrical equipment either sparks in normal operation or is liable to spark
under fault conditions.
Some electrical appliances such as electric heaters are specifically designed to
produce high temperatures.
These circumstances create fire and explosion hazards, which demand very
careful assessment in locations where processes capable of producing flammable
concentrations of gas or vapour are used, or where flammable liquids are stored.
It is likely that many fires are caused by static electrical discharges. Static
electricity can, in general, be eliminated by the careful design and selection of
materials used in equipment and plant, and the materials used in products being
manufactured. When it is impractical to avoid the generation of static electricity, a
means of control must be devised. Where flammable materials are present, especially
if they are gases or dusts, then there is a great danger of fire and explosion, even if
there is only a small discharge of static electricity.

Figure 14.4 - Modern multiplug.

The use of electrical equipment in potentially flammable atmospheres should
be avoided as far as possible. However, there will be many cases where electrical
equipment must be used and, in these cases, the standards for the construction of the
equipment should comply with the regulations.

Before electrical equipment is installed in any location where flammable

vapours or gases may be present, the area must be zoned in accordance with the
regulations.

4