Category: MK Electric Compliance with Part M
Building Regulations
MK Electric Compliance with Part M Building
Regulations Email
MK Electric
After approximately three years of consultation and
drafting, January 2008 saw the introduction of BS7671:2008, the 17th
Edition of the Institute of Electrical Engineers Wiring Regulations.
After an initial 6 month transitional period, the new regulations came
into full effect from the 1st July 2008.
RCDs have been installed in electrical installations for many years but
have become more commonplace since the 14th Edition of the IEE Wiring
Regulations and subsequent updates through the 15th and 16th Editions –
BS 7671.
But what is the role of the Residual Current Device? Although coming in
many guises put simply its job is to automatically disconnect the
electrical supply in the event of fault conditions for protection
against fire and harmful thermal effects within installations such as
agricultural premises but more commonly against Indirect Contact and for
supplementary protection against Direct Contact.
These two definitions will change with the publication of the 17th
Edition in January; Direct Contact will be known as “Basic Protection” –
protection from electric shock under fault free conditions whilst
Indirect Contact will be referred to as “Fault Protection” – protection
against electric shock under single fault conditions. However it is not
only these terms that will change, the use of RCDs is set to increase
dramatically with the advent of the 17th Edition.
As a necessary safety device the installation of RCDs has long been
required in instances where increased personal protection is required,
domestically to protect socket outlets and other electrical equipment
that is intended to be used for outside the home as well as “Special
Locations”, those areas where, for various reasons, increased risk of
electrical shock is present: swimming pools, saunas, construction sites,
horticultural premises and caravan parks and installations, these are
currently found in Part 6 of the 16th Edition but will now be found in
Part 7, with the new publication brought into line with the numbering of
IEC publications.
Part 7 will also include new areas such as marinas, exhibition stands,
fairgrounds and floor and ceiling heating systems where the use of RCDs
will be required.
In the name of safety the usage of RCDs is set to increase dramatically
in the forthcoming 17th Edition.
Three areas of the Regulations are set to address these concerns in a
major way; firstly Chapter 41 – Protection against Electric Shock – has
requirements for the additional protection of AC systems. Socket outlets
with a rated current not exceeding 20A for use for general purposes by
ordinary persons and mobile equipment with a current rating not
exceeding 32A for use outdoors are to be protected by an RCD with a
rated residual operating current not exceeding 30mA and an operating
time not exceeding 40mS at 5 x the rated operating current.
Exceptions are made for socket outlets under the supervision of skilled
or instructed persons or a specifically labelled or identified socket
outlet intended for the connection of a particular item of equipment.
Section 701 – Locations containing a Bath or Shower – has a requirement
for additional protection of all circuits within these areas by one or
more RCDs with the previously mentioned characteristics.
But probably the single largest impact can be found within Chapter 52 –
Selection and Erection of Equipment. In this instance protection by an
RCD, with the same characteristics as previous examples, is required to
protect all concealed cables in a wall or partition that are at a depth
of less than 50mm and run in the traditional “safe zones”; that is 150mm
from the top of a wall or partition, wall angle or the vertical and
horizontal runs to accessories and points. Safe Zones
There are exceptions to the required additional protection, namely if
the cable incorporates an earthed metallic covering complying with the
requirements for a circuit protective conductor, enclosed in earthed
conduit, enclosed in earthed ducting or be mechanically protected
sufficiently to prevent penetration of the cable by screws and nails.
Consider the average domestic installation, the final circuit cables
would generally be run in the “safe zones” at a depth less than 50mm but
are unlikely to be installed with one of the mechanically protected
options given, leaving all final circuits to be protected by a 30mA
rated RCD.
The time honoured provision of dividing an installation into circuits to
avoid danger and minimise inconvenience still applies as does the need
to reduce the possibility of unwanted tripping of an RCD by circuit
protective conductor currents produced by equipment in normal use.
Concealed Cables requiring RCD Protection
The installation designer may have to think very hard about circuit
protective arrangements and it may be that the use of RCBOs combining
residual and over-current protection become more commonplace as they
will provide both the necessary protection and avoid major inconvenience
as a fault condition will only operate one device.
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MK Electric
The Arnold Centre
Paycocke Road
Basildon
Essex
SS14 3EA UK
Tel: +44 (0) 1268 563000
Fax: +44 (0) 1268 563405
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+44 (0) 870 240 3385
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