TECHNICAL
Conductors, classificatio
Don Holmes
with the
second part
of his series
on the
definitions
found in part
2 of the new
wiring regs
My look at interpreting the 17th Edition Wiring
Regulations continues with another group of
definitions to which the new regulations refer to –
types of conductors used in electrical installations.
Typical ones for the following types of supplies listed
below are illustrated in Fig 1,2 and 3:
• multiphase
• multiphase and neutral
• single phase and neutral
When equipment is installed the same phase and
neutral reference is used as the distributors supply.
The circuit conductors to connect the incoming
supply to the equipment are called line and neutral
conductors. The definitions being as follows.
Line Conductor – a conductor of an ac system
for the transmission of electrical energy other than a
neutral conductor, a protective conductor or PEN
conductor. The term also means the equivalent
conductor of a dc system unless otherwise specified
by the regulations.
Neutral Conductor – a conductor connecting to
the neutral point of a system and contributing to the
transmission of an electrical energy. The term also
means the equivalent conductor of an IT or dc
system, unless otherwise specified in the regulations,
and also identifies the mid-wire of a three-wire dc
circuit or the earthed conductor of a two-wire earthed
dc circuit.
When we look at the definition of live conductor it
refers to the definition for Live Part.
Live Part – a conductor or conductive part
intended to be energised in normal use, including a
neutral conductor, but, by convention, not a PEN
conductor. This confirms that Line and Neutral
conductors are both live conductors when energised.
Fig 1
One of the references made in the wiring
regulations to phase and live conductors can be
found in Part 6 Inspection and Testing of the wiring
regulations. Regulation 612.12 states that a check of
phase sequence of multiphase circuits is required to
ensure it has been maintained. Regulation 612.3.1
states that when carrying out insulation resistance
testing, this shall be measured between live
conductors and between live conductors and
protective conductors.
Classification of persons
I shall now look at those wiring regulations referring to
the type of persons that can use or operate electrical
equipment and what provisions are required.
Competent person – a person possessing
sufficient technical knowledge, relevant practical
skills and experience for the nature of electrical
work undertaken and is able at all times to prevent
danger and, where appropriate, injury to him/herself
and others.
An example of the work only a competent person
may undertake can be found in Part 6 Inspection and
Testing of the wiring regulations. Regulation 621.5
states that periodic inspection and testing shall only
be undertaken by a competent person. Another
example is given in Chapter 63 Certification and
Reporting.
Regulation 631.4 states the following certificates
and reports shall be compiled and signed or
otherwise authenticated by a competent person:
• Electrical Installation Certificate
• Periodic Inspection Report
• Minor Electrical Installation Works Certificate:
Multiphase and neutral
Live conductors
3 phase and
neutral supplly
Phase conductor
Line conductor L1
L1
Neutral
Neutral conductor N
N
The definitions
for the distributors
installation are
from ‘The Electricity,
Safety, Quality
and Continuity
Regulations 2002’
Phase conductor
Line conductor L2
Phase conductor
Line conductor L3
Protective conductor
Protective conductor
L2
L3
Consumers equipment
(3 phase and neutral)
Distributor’s installation
14 NAPIT 0870 444 1392 www.napit.org.uk
Consumers installation
TECHNICAL
ons of people and live parts
Other definitions to note follow. Skilled person – a
person with technical knowledge or sufficient
experience to enable him/her to avoid dangers which
electricity may create.
Instructed person – a person adequately
advised or supervised by skilled persons to enable
him/her to avoid dangers which electricity may create.
Ordinary person – a person who is neither a
skilled nor an instructed person.
With the exception of competent person these
definitions are not new and appeared in the 16th
Edition of the wiring regulations, however greater
importance is given to them in the 17th Edition.
Examples of the use of these three definitions can
Fig 2
be found in Chapter 41 Protection Against Electric
Shock, Regulation 411.3.3 dealing with additional
protection. This states that socket-outlets rated at 20A
or less for use by ordinary persons and intended for
general use shall be provided with additional
protection by means of a 30mA RCD.
However exemptions are permitted when socket
outlets are used under the supervision of a skilled or
instructed person, such as some situations in
commercial or industrial locations. The other
exemption is when a socket-outlet has been provided
for a specific item of equipment such as a freezer. In
this case the socket-outlet shall be specifically
labelled to indicate this.
Multiphase
Live conductors
3 phase supplly
Phase conductor
Line conductor L1
L1
Phase conductor
Line conductor L2
Phase conductor
Line conductor L3
Protective conductor
Protective conductor
L2
L3
Consumers equipment
(3 phase)
Distributor’s installation
Fig 3
Consumers installation
Single phase and neutral
Live conductors
Single phase and
neutral supplly
Phase conductor
Line conductor L
L
Neutral conductor
Neutral conductor N
N
Protective conductor
Protective conductor
Consumers equipment
(Single phase and neutral)
Distributor’s installation
Consumers installation
NAPIT 0870 444 1392 www.napit.org.uk 15