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Good and effective earthing is absolutely essential and must be connected and checked by a
competent person. Where direct contact with the earth is not possible, for example, in a motor car,
a common voltage reference point is used, such as the vehicle chassis.
Where other potential metallic conductors exist near to electrical conductors in a building,
they must be connected to the main earth terminal to ensure the equipotential bonding of all
conductors to earth. This applies to gas, water and central heating pipes and other devices such as
lightning protection systems. Supplementary bonding is required in bathrooms and kitchens where,
for example, metal sinks and other metallic equipment surfaces are present. This involves the
connection of a conductor from the sink to a water supply pipe which has been earthed by
equipotential bonding. There have been several fatalities due to electric shocks from ‘live’ service
pipes or kitchen sinks.

Some definitions

Certain terms are frequently used with reference to electricity and the more
common ones are defined here.
Low voltage – a voltage normally not exceeding 600 V ac between conductors
and earth or 1000 V ac between phases. Mains voltage falls into this category.
High voltage – a voltage normally exceeding 600 V ac between conductors and
earth or 1000 V ac between phases.
Mains voltage – this is the common voltage available in domestic premises and
many workplaces and is normally taken from three-pin socket points. In the UK it is
distributed by the national grid and is usually supplied between 220 V and 240 V, ac
and at 50 cycles/s.
Maintenance – a combination of any actions carried out to retain an item of
electrical equipment in, or restore it to, an acceptable and safe condition.
Testing – a measurement carried out to monitor the conditions of an item of

electrical equipment without physically altering the construction of the item or the
electrical system to which it is connected.
Inspection – a maintenance action involving the careful scrutiny of an item of
electrical equipment, using, if necessary, all the senses to detect any failure to meet
an acceptable and safe condition. An inspection does not include any dismantling of
the item of equipment.
Examination – an inspection together with the possible partial dismantling of
an item of electrical equipment, including measurement and non-destructive testing
as required, in order to arrive at a reliable conclusion as to its condition and safety.
Isolation – involves cutting off the electrical supply from all or a discrete
section of the installation by separating the installation or section from every source
of electrical energy. This is the normal practice so as to ensure the safety of persons
working on or in the vicinity of electrical components which are normally live and
where there is a risk of direct contact with live electricity.
Competent electrical person – a person possessing sufficient electrical
knowledge and experience to avoid the risks to health and safety associated with
electrical equipment and electricity in general.

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