ELECTRICAL
TECHNICAL
Conducting locations with restricted
movement are classed as special locations
as the risk of electric shock is greatly
increased. Malcolm Doughton considers the
additional requirements for such locations
as detailed in BS 7671 Requirements for
Electrical Installations, Section 706.
Conducting
lessons
In most installations, access to
earthed metal and conducting
surfaces is fairly limited and
the contact area of the body is
generally comparatively low. As a
result the likelihood of receiving a
fatal electric shock is relatively small.
In a conducting location where
movement is restricted the
situation is quite different.
• There is little opportunity
to move away from the
contact/shock.
• Contact resistance is
reduced because the contact
area is increased.
• Contact resistance is often
lowered further due to
perspiration from the confined
location and/or damp
environmental conditions.
• Breathing can be seriously
affected as a result of electric
shock in these conditions.
• Current through the body will be
higher, so the risk of ventricular
fibrillation is also increased.
i
NOTE
It is important to
remember that references to
‘the location’ in this article refer
only to the conducting location
with restricted movement
and not any other part of the
building structure within which
the special location is contained.
As a result of the additional risk
associated with these locations,
they are considered to be a
special location with additional
risk of electric shock.
One of the main considerations
here is that the work being
carried out in these locations is
often done by persons who are
not electrically skilled. However,
the activities will generally require
some form of task lighting and
often involve the use of electrical
tools and equipment.
There are certain locations that
contain fixed electrical equipment,
and the requirements here apply
not only during construction but
also in the use and maintenance
of the equipment.
The first stage is to establish
whether a particular location is
in fact a conducting location with
restricted movement and – as
such – whether the associated
additional requirements need to
be applied.
In order to qualify for the
requirements of such a location,
it must include:
• A conducting location that is
comprised of mainly metallic
or other conductive parts.
• Within the location, a
substantial portion of a person
will come into contact with the
conducting surface.
35
ELECTRICAL
TECHNICAL
Figure 1. The construction of specialised components will require work to
be carried out in locations with restricted movement.
• The possibility of breaking
the contact between the body
and the conducting surface
is limited.
The additional requirements will
only apply where the location
comprises both the ‘mainly
conductive construction’ and
the ‘restriction of movement’
conditions. Therefore, being
simply a tight space such as an
under-stair cupboard, for example,
would not qualify.
Similarly, a location that is
constructed of conductive
material but also allows freedom
of movement – such as a metal
store or warehouse – would
not be subject to the additional
requirements.
The author
Malcolm Doughton, I.Eng.
MIET, LCGI, trained as an
electrician with Eastern
Electricity, then worked for an
independent contractor. This
was followed by a number
of years lecturing in further
education in both electrical
installation and heavy current
engineering then moving
back into industry as Senior
Electrical Design Engineer
with an international M&E
contractor. Malcolm later
moved into the regulatory
sector as a Senior Engineer.
Now with over 40 years
experience in the industry,
Malcolm is director of an
electrical consultancy, safety
and training company.
36 › INSTALLER › April 2014
The particular requirements
will not apply where the location
allows freedom of bodily
movement while working and the
ability to enter and leave without
physical restraint.
In addition, there are certain
electrical systems as defined in
BS 7909 Code of practice for
temporary electrical systems
for entertainment and related
purposes that are subject to the
requirements of BS 7009 and so
are not subject to BS 7671 Section
706. These systems include
mobile units used for public or
private events, touring shows, TV,
film, theatre or radio production.
i
NOTE
Further information
on the installation and use of
arc welding equipment can be
found in BS EN 60974-9: 2010
Arc welding equipment
installation and use.
Subject to these considerations,
the particulars of Section 706
apply to fixed equipment in
conducting locations where
movement of persons is
restricted by the location, and
supplies for mobile equipment for
use in such locations.
Construction
This includes the construction
of specialised components such
as diving spheres and cement
lorry drums (see Figure 1).
These are often constructed in
factory conditions where the
equipment and supplies used can
be formalised and maintained.
However, the same criteria and
requirements will apply when
the work is undertaken within
Figure 2. Equipment used during maintenance and repair work must
meet specific requirements. (Photo: Gazprom)
a conducting location with
restricted movement.
The construction of metal
pipelines and steel structures
often results in work being carried
out in conductive locations where
there is restricted movement.
As this work is carried out on site,
the monitoring of the installation,
which is often temporary in nature,
is of significant importance.
It is essential that these areas
are suitably prepared, and
both appropriate supplies and
equipment are used.
Maintenance and repair
Common maintenance activities
include such work as the
maintenance of large boilers and
cleaning of cement lorry drums,
where the task is removing
residue and build-up of materials.
This type of maintenance work is
often carried out on site, and the
tools and equipment used must
meet the specific requirements in
order to ensure the safety of the
operatives involved.
Repairs are often carried out
that involve cutting, drilling and
welding (see Figure 2). Again,
it is important that these areas
are suitably prepared, and
both appropriate supplies and
equipment are used.
Additional requirements are
detailed in BS 7671 for both fixed
equipment and hand-held tools
or mobile equipment. The use of
obstacles or ‘placing out of reach’
are not permitted as protective
measures in these locations.
Fixed equipment
There are a number of
permissible protective measures
for the fixed equipment.
• Electrical separation
This method may be used
providing only one item of
equipment is connected to
a secondary winding of the
transformer. The unearthed
source should have at least
simple separation and be
placed outside the location
(unless it is part of the location’s
fixed electrical installation).
››The use of
obstacles or ‘placing
out of reach’ are
not permitted as
protective measures
in these locations.‹‹
• Use of Class II equipment
or equipment having
equivalent insulation
This option may be used
providing the circuits supplying
the equipment have additional
protection through the use of
an RCD with a rated residual
operating current not exceeding
30mA and that will disconnect
within 40 ms when tested at
five times its rated residual
operating current.
• Automatic disconnection
of supply (ADS)
This method may be
used providing there is
supplementary equipotential
bonding installed that connects
the exposed conductive
parts of fixed equipment and
the conductive parts of the
location. Where a functional
earth is required for certain
items of equipment, this must
also be connected to the
supplementary bonding.
• Protective extra-low voltage
(PELV) or Separated extra-low
voltage (SELV)
For SELV or PELV, irrespective
of the nominal voltage, basic
protection or suitable barriers
and enclosures must be
provided (in accordance with
BS 7671, Regulations 416.1
and 416.2). Also, the source of
SELV or PELV must be situated
outside the location (unless it
is part of the location’s fixed
electrical installation).
Where PELV is used, there
must also be equipotential
bonding provided which
connects all the exposed
conductive parts within the
location to the earth connection
of the PELV system.
Mobile equipment
The following protective measures
are permitted for hand-held and
mobile equipment.
• Electrical separation
Electrical separation may be
used providing that only one
item of equipment is connected
to each secondary winding of
the transformer. Transformers
may have more than one such
winding but only one item of
equipment may be connected
to each winding.
• Separated extra-low
voltage (SELV)
Hand-held and portable
equipment can be supplied
at SELV (maximum 55V AC
supplied via an isolating
transformer).
• Handlamps must be supplied
at SELV, but it is acceptable
for a SELV circuit to supply a
fluorescent luminaire with an
in-built, step-up transformer
that has electrically separated
windings.
One of the additional
requirements that is easily
overlooked when working in
these locations is the need for
supplementary bonding. It is
often assumed that because
an item of equipment has been
provided for the task, this is all
that is necessary. Due to the
nature of the supply equipment
being used, where there is a need
for supplementary bonding to
be installed, this must be made
known to the operative.
The correct installation of
the bonding, in all but the most
basic of circumstances, will need
to be confirmed by a person
electrically competent to do so.
For these reasons, those systems
that require the installation of
supplementary bonding may not
be appropriate for certain types
of activity. n
TO SUM UP
› Conducting locations with restricted movement are
classed as special locations as the risk of electric shock is
greatly increased.
› Work in these locations is often done by persons who are
not electrically skilled.
› Conducting locations with restricted movement.
› Location is comprised mainly of metallic or other
conductive parts.
› A person within the location will come into contact with a
substantial portion of the conducting surface.
› The possibility of breaking the contact between the body
and the conducting surface is limited.
› The additional requirements of BS 7671, Section 706 must
be observed.
› Handlamps must be supplied at SELV.