Introduction to Health and Safety at Work

Introduction to Health and Safety at Work
194
Where plugs and sockets are used for portable tools, 
suffi cient sockets must be provided for all the equipment 
and adaptors should not be used. Many accidents are 
caused by faulty fl exible cables, extension leads, plugs 
and sockets, particularly when these items become 
damp or worn. Accidents often occur when contact is 
made with some part of the tool which has become live 
(probably at mains voltage), while the user is standing on, 
or in contact with, an earthed conducting surface. If the 
electric supply is at more than 50 V ac, then the electric 
shock that a person may receive from such defective 
equipment is potentially lethal. In adverse environmental 
conditions, such as humid or damp atmospheres, even 
lower voltages can be dangerous. Portable electrical 
equipment should not be used in fl ammable atmospheres 
if it can be avoided and it must also comply with any 
standard relevant to the particular environment. Air 
operated equipment should also be used as an alterna-
tive whenever it is practical.
Some portable equipment requires substantial 
power to operate and may require voltages higher than 
those usually used for portable tools, so that the current 
is kept down to reasonable levels. In these cases, power 
leads with a separate earth conductor and earth screen 
must be used. Earth leakage relays and earth monitoring 
equipment must also be used, together with substantial 
plugs and sockets designed for this type of system.
Electrical equipment is safe when properly selected, 
used and maintained. It is important, however, that 
the environmental conditions are always carefully con-
sidered. The hazards associated with portable appliances 
increase with the frequency of use and the harshness of 
the environment (construction sites are often particu-
larly hazardous in this respect). These factors must be 
considered when inspection, testing and maintenance 
procedures are being developed.