System Listings
Earthing & Bonding
![[Image]](../graphics/system.jpg)
System
Overview
This system comprises the cabling and equipment necessary to ensure
that the whole installation is as safe as is reasonably practical against
metalwork becoming live (including parts not necessarily forming part of
the installation).
There are numerous terms applicable earthing & bonding. The main definitions
are as follows:
-
Circuit Protective Conductor
(CPC) - A conductor that is installed in order to provide a guaranteed
earth return path for an individual circuit. Thereby ensuring fast disconnection
times.
-
Bonding Conductors. Conductors
that are installed to electrically link items of metalwork within a building
thereby ensuring that an earth fault has a minimum return resistance. Further
divided into Equipotential Bonding and Supplementary Bonding.
Adequate bonding ensures fast disconnection times and that the touch voltage
between metalwork does not exceed 50volts.
-
Clean
earth - this is a specialised form of CPC that is installed to serve
sensitive electronic equipment.
Systems Available and
Applications
Earthing systems need special consideration within the building
if they are to remain intact and operational.
-
Circuit Protective Conductor.The CPC can be either a separate
conductor installed alongside the circuit conductors in which case it is
required that the conductor insulation is coloured green and yellow. It is
also possible to use metallic containment within which the circuit conductors
are installed (such as conduit). In such a case it must be ensured by means
of calculation that the cross sectional area of the metal is big enough to
provide a sufficiently low earth return resistance.
-
Bonding Conductors. Electrical bonding may be carried
out by a range of means depending upon the type of building and equipment
installed. Common means of linking steel frameworks and equipment is
with the use of earthing
strap
or
separate conductors connected together using lugs and nuts &
bolts.
Pipework, conduits etc. may be bonded using custom earth
clips.
-
Earth
Electrodes. Where the supply authority does not provide an adequate earth,
or where the remote nature of the site dictates or where the building user
owns the substation, it is necessary to install earth electrodes. These are
typically lengths of copper rod which are driven into the ground to make
a good connection with the general mass of earth.
Legislation &
Guidelines
British Standards.
Also refer to The
British Standards Institution
-
BS 7430:1991 "Code of practice for earthing". Guidance on earthing of electrical
supply systems,electrical installations and connected equipment, for the
proper operation of systems and the protection of human and animal life.
Covers basic principles, earthing methods and most general applications.
Certain special applications are covered only by references to other
standards.
-
BS 951:1986 "Specification for clamps for earthing and bonding purposes".
Performance and important mechanical features of metal clamps used to provide
mechanically and electrically sound means of earthing and or bonding, using
conductors of 2.5 mm² to 70 mm² cross-sectional area secured via
the use of screw-threads only, and attached to tubes of 6 mm diameter and
above
International Standards
Refer to the IEC search page
Legislation
-
Health & Safety at Work Act 1974 - Massive item of legislation
which encompasses all aspects of Health & Safety in the workplace. This
has been constantly added to over the years. It now comprises and references
a whole series of separate regulations and codes of practice documents
-
Electricity Act
1989 - In the words of the official HMSO title. "An Act to provide for
the appointment and functions of a Director General of Electricity Supply
and of consumers' committees for the electricity supply industry; to make
new provision with respect to the supply of electricity through electric
lines and the generation and transmission of electricity for such supply;
to abolish the Electricity Consumers' Council and the Consultative Councils
established under the Electricity Act 1947; to provide for the vesting of
the property, rights and liabilities of the Electricity Boards and the
Electricity Council in companies nominated by the Secretary of State and
the subsequent dissolution of those Boards and that Council; to provide for
the giving of financial assistance in connection with the storage and
reprocessing of nuclear fuel, the treatment, storage and disposal of radioactive
waste and the decommissioning of nuclear installations; to amend the Rights
of Entry (Gas and Electricity Boards) Act 1954 and the Local Government
(Scotland) Act 1973; and for connected purposes."
-
Supply regulations 1989. - A set of regulations relating to the
obligations of the Regional Electricity Companies and the supply of electricity
to both industrial & domestic consumers.
-
Electricity at Work Regulations 1989 - Regulations covering the whole
aspect of ensuring that the workplace is safe in regards to the use of electrical
equipment. (a part of the H&S at Work act)
-
Construction (design & management) regulations 1994 - Another
wide reaching set of regulations which cover the whole process of construction
safety. It focuses on carrying out risk assessments and altering the design
or management process to account for such risks. Again this forms part of
the H&S at work act 1974.
Related
Links
Links relating to the design and installation of earthing & bonding systems
can be found here
Manufacturers
The correct installation of earthing & bonding systems mostly relies
on the design and/or installation engineer ensuring that the system is compliant
with the relevant legislation. The equipment used is mostly from general
ranges of manufactures equipment.
General electrical installation equipment manufacturers are listed
here
