WIRING
MATTERS
Winter 07 Issue 25
FAIRGROUNDS,
AMUSEMENT PARKS
AND CIRCUSES
The impact of the17th Edition
of the Wiring Regulations
Solar Photovoltaic Power
Supply Systems
Protective Conductor Currents
17th EDITION
1
public supply is given in ESQCR 2002.
For sets above 16A the requirements of
the distributor must be ascertained.
The 17th Edition recognises that
there are two connection options:
(i) connection into a separate
dedicated circuit.
(ii) connection into an existing final
circuit.
Connection into a dedicated circuit
is preferred. Regulation 551.7.2 sets out
the requirements for the two options.
The Regulation requires that a
generating set used as an additional
source of supply in parallel with
another source shall either be installed
on the supply side of all protective
devices for the final circuits of the
installation (connection into a separate
dedicated circuit) or if connected on
the load side of all protective devices
for the final circuits must fulfil a
number of additional requirements.
THE IMPACT OF THE
17TH EDITION OF THE
WIRING REGULATIONS
by Geoff Cronshaw
IN THIS second article we look at
more of the changes expected in the
17th Edition of the IEE Wiring
Regulations and the impact these will
have on the design, erection and
verification of electrical installations.
This article is generally based on the
Draft for Public Comment and therefore
the actual requirements may change.
Chapter 55 – other equipment.
Regulation 551 – Low voltage
generating sets
This set of Regulations now includes
additional requirements contained in
Regulation 551.2 to ensure the safe
connection of low-voltage generating
sets including small scale embedded
generators.
A new Regulation 551.4.2, regarding
the use of RCDs, has been added.
Regulation 551.4.2 states: the
generating set shall be connected so
that any provision within the
installation for protection by RCDs in
accordance with Chapter 41 remains
effective for every intended
combination of sources of supply.
Notes have been added including one
to Regulation 551.1 stating that the
procedure for connecting generating
sets up to 16A in parallel with the
These additional requirements are:
(i) the current carrying capacity of
the final circuit conductors shall
be greater than or equal to the
rated current of the protective
device plus the rated output of the
generating set and
(ii) A generating set shall not be
connected to a final circuit by a
plug and socket and
(iii) A residual current device providing
additional protection of the final
circuit in accordance with
Regulation 415.1 shall disconnect all
live conductors including the
neutral conductor and
(iv) The line and neutral conductors of
the final circuit and of the
generating set shall not be
connected to earth and
(v) Unless the device providing
automatic disconnection of the
final circuit in accordance with
Regulation 411.3.2 disconnects the
line and neutral conductors, it
shall be verified that the
combination of the disconnection
time of the protective device for 왘
IEE Wiring Matters | Winter 07 | www.theiet.org
17th EDITION
2
왗 the final circuit and the time
taken for the output voltage of the
generating set to reduce to 50V or
less is not greater than the
disconnection time required by
Regulation 411.3.2 for a final
circuit.
Section 559 luminaries and
lighting installations
Section 559 luminaries and lighting
installations is a new series of
Regulations giving particular
requirements for fixed outdoor
lighting installations, extra-low
voltage lighting installations, and
lighting for display stands.
Section 559 includes requirements
from Regulations 553-03 (lampholders)
and 553-04 (lighting points) in the 16th
Edition. This new section also
includes requirements from Section
611 (Highway Power Supplies and
Street Furniture) of the 16th Edition.
The impact of this new section is
that additional requirements are now
included in the Regulations for
general lighting including
requirements for protection against
fire, connection of luminaires to the
fixed wiring, fixing of the luminaires,
requirements for through wiring in a
luminaire, requirements for control
gear eg ballasts, and compensation
capacitors. A further new
requirement is the need to give
consideration to stroboscopic effects.
The Regulations for outdoor
lighting installations has been
expanded compared to Section 611 in
the 16th Edition, to cover, car parks,
gardens, parks, places open to the
public, illumination of monuments
and floodlighting. Other lighting
arrangements specifically mentioned
include telephone kiosks, bus shelters,
advertising panels and town plans,
which it is recommended are provided
with additional protection by a 30mA
RCD.
Regulation group 559.11 is a
completely new series of Regulations
that were not included in the 16th
edition covering requirements for
extra-low voltage lighting
installations. The particular
requirements of these Regulations
apply to extra-low voltage lighting
installations supplied from sources
with a maximum rated voltage of
50 V ac rms or 120 V dc
The Regulations include
requirements for protection against
electric shock (SELV), protection
against the risk of fire due to short
circuit, types of wiring systems
including special requirements where
bare conductors are used, the types of
transformers and converters, and
requirements for suspended systems.
New sections on special locations
The 17th Edition includes additional
sections on special locations not
currently included in the 16th Edition
as follows:
Marinas
Photovoltaic power systems
Exhibitions, shows and stands
Floor and ceiling heating systems
Mobile and transportable units
Fairgrounds, amusement parks and
circuses
Marinas: There are particular risks
associated with electrical installations
in marinas. The environment of a
marina or yachting harbour is harsh
for electrical equipment. The water,
salt and movement of structures
accelerate deterioration of the
installation. The presence of salt
water, dissimilar metals and a
potential for leakage currents
increases the rate of corrosion. There
are also increased electric shock risks
associated with a wet environment, by
reduction in body resistance and
contact with earth potential. Site
investigations should be carried out at
an early stage to determine likely
maximum wave heights. This is of
particular importance in exposed
coastal sites. Where marinas have
breakwater type pontoons, it is likely
that under certain conditions waves
will pass over the structure.
The risks specifically associated
with craft supplied from marinas
include:
i) Open circuit faults of the PEN 왘
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IEE Wiring Matters is a quarterly publication from the Institution of Engineering and Technology (IET). The IET is not as a body responsible for
the opinions expressed.
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ISSN 1749-978-X
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PWRRFP73
17th EDITION
4
conductor of PME supplies
raising the potential to true earth
of all metalwork (including that of
the craft, if connected) to
dangerous levels
ii) Inability to establish an
equipotential zone external to the
craft
iii) Possible loss of earthing due to
long supply cable runs, connecting
devices exposed to weather and
flexible cord connections liable to
mechanical damage.
Particular requirements to reduce
the above risks include:
i ) Prohibition of a TN-C-S system for
the supply to a boat. (Regulation
709.411.4)
ii ) Additional protection by 30 mA
RCDs in both the craft and the
marina installation. (Regulation
709.531.2)
iii) outlets to be installed at not less
than 1m above the highest water
level. (Regulation 709.553.1.13 does
give certain exceptions.)
There are also additional
requirements to meet the conditions
of external influences.
PV supply systems
This section applies to the electrical
installations of PV power supply
systems including systems with ac
modules. Stand alone systems are still
under consideration.
This section includes the following
additional measures:
Regulation 712.410.3 – PV equipment
on the dc side shall be considered to be
energised, even when the system is
disconnected from the ac side.
Regulation 712.410.3.6 – The protective
measures of non conducting location
and earth free local equipotential
bonding are not permitted on the dc side.
Regulation 712.411.3.2.1.1 – On the ac
side, the PV supply cable shall be
connected to the supply side of the
device supplying current using
equipment.
IEE Wiring Matters | Winter 07 | www.theiet.org
Regulation 712. 537. 2.1.1 – To allow
for maintenance, means of isolating
the ac and dc sides of the PV
convertor shall be provided.
There are also additional requirements for accessibility, external
influences, routing of protective
conductors, selection and erection of
cables to avoid the risk of lightning
strike, short-circuit and earth faults,
overcurrent protection, compliance
with standards, protection against
electromagnetic interference and
devices for isolation.
For detailed requirements of this
section please refer to the specific
article concerning PV systems in this
edition of Wiring Matters.
Exhibitions, shows and stands
The risks associated with exhibitions,
shows and stands are those of electric
shock and fire. These arise from:
1. the temporary nature of the
installation
2. lack of permanent structures
3. severe mechanical stresses
4. access to the general public.
Because of these increased risks
additional measures are required.
Regulation 711.410.3.4 – A cable
intended to supply temporary
structures shall be protected at its
origin by an RCD with maximum
residual operating current 300mA.
Regulation 711.3.1.2 – Bonding of all
metallic structural parts which are
accessible within the stand etc.
Regulation 711.3.3 – Additional
protection is required for all final
circuits and sockets-outlets up to 32A
by RCD to 415.1.1.
Regulation 711.411.4 – TN-C-S shall
not be used.
Regulation 711.537.2.3 – every temporary structure, such as a vehicle,
stand or unit, intended to be occupied
by one specific user and each
distribution circuit supplying outdoor
installations shall be provided with its
own readily accessible and properly
identifiable means of isolation.
Floor and Ceiling Heating Systems
This Section applies to the installation
of electric floor and ceiling heating
systems; it does not apply to wall
heating or outdoor heating systems.
The risks associated with ceiling
heating systems are generally that of
penetration of the heating element by
nails, drawing pins, etc pushed through
the ceiling surface. For this reason
Regulation 753.411.3.2 requires RCDs
with a maximum rated residual
operating current of 30mA shall be
used for automatic disconnection of
supply.
Similarly, there are concerns that
under-floor heating installations can
be damaged by carpet gripper nails,
etc and for similar reasons protection
by a 30 mA RCD is required. To
protect the building structure and
provide precautions against fire,
there are requirements to avoid
overheating of the floor or ceiling
heating system.
Heating units manufactured without
exposed conductive parts shall be
provided on site with a grid with
spacing of not more than 30mm, or
other suitable conductive covering
above the floor heating or below the
ceiling heating and connected to the
protective conductor of the
installation.
Mobile and transportable units
The particular requirements of this
Section apply to mobile or
transportable units. These may be selfpropelled, towed or transportable
containers or cabins.
Examples of the units include
technical and facilities vehicles for the
entertainment industry, medical
services, advertising, fire fighting,
workshops, offices, transportable
catering units etc.
The risks associated with mobile
and transportable units include:
Risk of loss of connection to earth due
to use of temporary cable connections,
risks arising from the connection to
different national and local electricity
17th EDITION
5
distribution networks, impracticality
of establishing an equipotential zone
external to the unit, open-circuit faults
of the PEN conductor of PME supplies
raising the potential of all metalwork
(including that of the unit) to
dangerous levels, risk of shock arising
from high functional currents flowing
in protective conductors, and
vibration while the vehicle or trailer is
in motion, or while a transportable
unit is being moved – causing faults
within the unit installation.
Some of the requirements to reduce
these risks include:
Regulation 717.411.1 Automatic
disconnection shall be by RCD.
Regulation 717.411.3.1.2 Accessible
conductive parts of the unit to be
connected through the main
equipotential bonding to the main
earth terminal within the unit.
Regulation 717.514 Identification
adjacent to the supply inlet:
(i) The type of supply which may be
connected.
(ii) The voltage rating of the unit.
(iii) The number of phases and their
configuration.
(iv) The on board earthing
arrangements.
(v) The maximum power required by
the unit.
Persons involved in mobile or
transportable units will need to refer
to section 717 of the 17th edition of the
Wiring Regulations.
Fairgrounds, amusement parks
and circuses
This Section specifies the minimum
electrical installation requirements to
facilitate the safe design, installation
and operation of temporary erected
mobile or transportable electrical
machines and structures which
incorporate electrical equipment. The
machines and structures are intended to
be installed repeatedly, without loss of
safety, temporary, at fairgrounds,
amusement parks, circuses or similar
places. The permanent electrical
installation is excluded from the scope.
This section does not apply to the
internal electrical wiring of the
machines.
For detailed requirements of this
section please refer to the specific
article concerning fairgrounds,
amusement parks and circuses in this
edition of Wiring Matters.
More information.
Important: this article only considers
a small number of changes expected
in the 17th Edition. For more
information refer to IET website,
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FAIRGROUNDS
6
internal electrical wiring of machines
(see BS EN 60204-1).
Electrical Supplies
The nominal supply voltage of
temporary electrical installations in
booths, stands and amusement devices
should not exceed 230/400 V ac or
440 V dc. Supplies can be obtained
from a number of sources:
from the public network,
i.e. the DNO
generators, i.e. those mounted on
trucks owned by the touring event
from privately owned supplies, i.e. a
local factory with sufficient sparecapacity
FAIRGROUNDS,
AMUSEMENT PARKS
AND CIRCUSES
by Mark Coles
THIS ARTICLE looks at
Temporary Electrical Installations for
Structures, Amusement Devices and
Booths at Fairgrounds, Amusement
Parks and Circuses – a proposed new
Section for BS 7671:2008, 17th Edition
of the IEE Wiring Regulations.
Currently, there is no Part or Section
of BS 7671:2001(2004) covering such
installations but information can
be found in IEC 60364-7-740 and
HD 60364-7-740.
The proposed Section 740 of BS
7671:2008 is based on the CENELEC
Harmonised Document HD 60364-7-740,
of which, the UK is to incorporate the
technical intent of that standard.
(Please note that Regulations
and Sections quoted within this
article are from the proposed BS
7671:2008 and may be subject to
change).
IET Wiring Matters | Winter 07 | www.theiet.org
The Scope of Section 740
Section 740 recognises that some
installations are exposed to many
differing and onerous circumstances,
as they are frequently installed,
dismantled, moved to a new location
then installed and operated again.
To compound problems, such
installations can be exposed to the
elements, open to the general public,
house animals and livestock and be
operated as a place of work. The
equipment must function without
compromising safety, therefore, the
installation has to be fit for purpose
and be designed to cope with
ever-changing conditions.
The permanent electrical
installation, from which the temporary
system is supplied, or the building in
which the temporary system is
housed, is excluded from the scope,
nor does the scope apply to the
There can be any number of
electrical sources supplying the
temporary system and it is of
paramount importance that line-andneutral conductors from different
sources are not interconnected. Where
the supply is obtained from the DNO
any instructions given must be
adhered to.
Supplies obtained from the DNO
would preferably be TN-S but this isn’t
always possible. A TN-S system has the
neutral of the source of energy
connected with earth at one point only,
at, or as near as is reasonably
practicable, to the source of supply. The
consumer’s main earthing terminal is
typically connected to the metallic
sheath of the distributor’s SWA service
cable.
Where the available supply is
TN-C-S, the supply should not be used
in that form, i.e. a TT system should be
created. The reason is that the ESQCR
prohibits the use of a TN-C-S system
for the supply of a caravan or similar
construction.
Where continuity of service is
important, IT systems may be used for
dc applications only.
Protection against electric shock
At the origin of each electrical supply,
to all or part of the installation, an
RCD, with a rated residual operating 왘
FAIRGROUNDS
8
왗 current not exceeding 300 mA, is to
be installed to provide automatic
disconnection of supply. As there will
be further RCDs downstream of this
point, this RCD should be of the
S-type, complying with the
requirements of BS EN 61008-1 or BS
EN 61009-1 and incorporate a time
delay in accordance with BS EN 60947-2,
to provide discrimination with further
RCDs protecting final circuits.
For supplies to ac motors, RCDs
should be the time-delayed or the
S-type where necessary to prevent
unwanted tripping.
The protective measure of
protection by obstacles is not
permitted on this type of installation,
however, placing out of arm’s reach is
acceptable for electric dodgems – more
of which later.
Additional protection
All final circuits in the installation,
e.g. lighting, socket-outlets rated up to
32 A, mobile equipment connected by a
flexible cable and rated up to 32 A are
to be protected by an RCD having a
rated residual operating current not
exceeding 30 mA. The requirement
for additional protection relates to the
increased risk of damage to
cables within an installation of this
nature.
Lighting circuits incorporating
emergency luminaires, with selfcontained batteries for example,
should be protected by the same RCD
protecting that lighting circuit.
This requirement for additional
protection does not apply to:
SELV or PELV circuits – this
measure alone is deemed to be a
protective measure in all situations
circuits protected by electrical
separation
lighting circuits placed out of arm’s
reach – provided they are not
supplied by socket-outlets, i.e. those
manufactured to BS 1363 or
BS EN 60309-1; luminaire supporting
couplers or plug-in lighting
distribution units excepted
IET Wiring Matters | Winter 07 | www.theiet.org
BS EN 60332-1-2. Cables of type
H07RNF or H07BN4-F (BS 7919)
together with conduits complying with
BS EN 61386-23 are deemed to satisfy
this requirement. Cables should have a
minimum rated voltage of 450/750 V,
except that, within amusement
devices, cables and cords having a
minimum rated voltage of 300/500 V
may be used. Where cables are buried
in the ground, the route should be
marked at suitable intervals and be
protected against mechanical damage.
Supplementary bonding
Particular care must be taken in areas
where livestock are housed as they are
sensitive to small potential differences.
To minimise potentials,
supplementary bonding should be
installed to connect all exposedconductive-parts and extraneousconductive-parts that can be touched
by livestock.
Where a metal grid is laid in the
floor, or extraneous-conductive-parts
are accessible, they should be included
within the supplementary bonding of
the location. It is important to note
that animal excrement and urine
is very corrosive and so all
supplementary bonding connections
should be enclosed in a suitable
enclosure.
THE INSTALLATION
Wiring systems
Conduit, cable trunking and ducting,
tray and ladder systems can be used
but must, of course comply with the
manufacturer's instructions; the
following standards apply:
conduit systems BS EN 61386 series
cable trunking systems/cable
ducting systems BS EN 50085
(particular parts only)
tray and ladder systems BS EN 61537
Cables
All cables should be fire rated
and meet the requirements of
Electrical connections
Joints should not be made in cables
except where necessary as a
connection into a circuit. Where joints
are made, these should be either using
connectors in accordance with the BS
7671, the manufacturer’s instructions
or the connection should be made in
an enclosure with a degree of
protection of at least IP4X or IPXXD.
Where strain can be transmitted to
terminals the connection should
incorporate cable anchorage(s).
External influences
Electrical equipment should have a
degree of protection of at least IP44.
Switchgear and controlgear
Switchgear and controlgear should be
placed in cabinets which can be
opened only by the use of a key or a
tool, except for those parts designed
and intended to be operated by
ordinary persons.
Isolation
It is a requirement that every
electrical installation of a booth, stand
or amusement device has its own
means of isolation, switching and
overcurrent protection, these devices
should be readily accessible. There are
similar requirements for supplies to
amusement devices. Additionally, each
distribution circuit should be provided
with its own readily accessible and
properly identified means of isolation.
A device for isolation should
FAIRGROUNDS
9
disconnect all live conductors – line(s)
and neutral conductors.
Examples of devices used for
isolation are:
circuit-breaker
RCD
plug and socket arrangement
Luminaires
Every luminaire and decorative
lighting festoon-chain should have a
suitable IP rating and be securely
attached to the structure or support
intended to carry it. Its weight should
not be carried by the supply cable,
unless it has been selected and erected
for this purpose.
Luminaires and decorative lighting
festoon-chains mounted less than
2.5 m, i.e. arm’s reach, above floor level
or could be otherwise accessible to
incidental contact, should be firmly
fixed, sited and guarded to prevent
risk of injury to persons or ignition of
materials. Access to the fixed light
source should only be possible after
removing a barrier or an enclosure,
which should only be possible by the
use of a tool. Lighting festoon-chains
should use H05RN-F (BS 7919) cable or
equivalent, they may be used in any
length provided the overcurrent
protective device in the circuit is
correctly rated.
Luminous tube, sign or lamps with
an operating voltage higher than
230 V/400 V a.c., e.g. neon signs, are to
be installed out of arm’s reach or be
adequately protected from accidental
or deliberate damage. A separate
circuit should be used which should be
controlled by an emergency switch.
The switch should be easily visible,
accessible and marked in accordance
with the requirements of the local
authority.
Luminaires in shooting galleries
and other sideshows where projectiles
are used should be suitably protected
against accidental or deliberate
damage.
When transportable floodlights are
used, they should be mounted so that
the luminaire is inaccessible to noninstructed persons. Supply cables
should be flexible and have adequate
protection against mechanical
damage.
Safety isolating transformers
and electronic converters
Safety isolating transformers should
comply with BS EN 61558-2-6 or
provide an equivalent degree of safety.
Each transformer or electronic
converter should incorporate a
protective device which can be
manually reset only; this device
should protect the secondary circuit.
Safety isolating transformers should
be mounted out of arm’s reach or be
mounted in a location that provides
equal protection, e.g. in a panel or
room that can only be accessed by a
skilled or instructed person, and
should have adequate ventilation.
Access by competent persons for
testing or by a skilled person
competent in such work for protective
device maintenance should be
provided.
Electronic converters should
conform to BS EN 61347-2-2.
Enclosures containing rectifiers and
transformers should be adequately
ventilated and the vents should not be
obstructed when in use.
Plugs and socket-outlets
An adequate number of socket-outlets
should be installed to allow the user's
requirements to be met safely. In
booths, stands and for fixed
installations, one socket-outlet for each
square metre or linear metre of wall is
generally considered adequate. Socketoutlets dedicated to lighting circuits
placed out of arm’s reach should be
labelled according to their purpose.
When used outdoors, plugs, socketoutlets and couplers should comply
with BS EN 60309-2, or where
interchangeability is not required,
BS EN 60309-1.
FIRE RISK
Luminaires and floodlights
Luminaires and floodlights should are
to be fixed so that a focusing or
concentration of heat is not likely to
cause ignition of any material.
Electric motors
An electric motor which is
automatically or remotely controlled
and which is not continually
supervised should be fitted with a
manual reset protective device against
excess temperature.
ELECTRICAL EQUIPMENT
Electrical supply to devices
At each amusement device, there
should be a connection point readily
accessible and permanently marked to
indicate the following essential
characteristics:
rated voltage
rated current
rated frequency
Electric dodgems
Electric dodgems should only be
operated at voltages not exceeding
50 V a.c. or 120 V d.c. The circuit
should have an electrical separation
from the electrical supply by means of
a safety isolating transformer in
accordance with BS EN 61558-2-4 or a
motor-generator set.
Low voltage generating sets
It is very important that all generators
are located to prevent danger and
injury to people through inadvertent
contact with hot surfaces and
dangerous parts. The electrical
equipment associated with the 왘
IET Wiring Matters | Winter 07 | www.theiet.org
FAIRGROUNDS
10
generator should be mounted
securely and, if necessary, on
anti-vibration mountings.
Where a generator supplies a
temporary installation, forming part
of a TN, TT or IT system, care should
be taken to ensure that the earthing
arrangements are adequate and, in
cases where earth electrodes are used,
they are considered to be continuously
effective. In reality this means that the
drying of the ground, in summer, or
freezing of the ground, in winter,
should not adversely affect the value of
earth fault loop impedance for the
installation.
The neutral conductor of the starpoint of the generator should, except
for IT systems, be connected to the
exposed-conductive-parts of the
generator.
INSPECTION AND TESTING
The temporary installation
The electrical installation between its
origin and any electrical equipment
should be inspected and tested after
each assembly on site. Internal
electrical wiring of roller coasters,
electric dodgems, etc., are not
considered as part of the verification
of the electrical installation. In special
cases the number of the tests may be
modified according to the type of
temporary electrical installation.
The HSE offers guidance on the
inspection and testing of the temporary electrical installation in the
publication HSG 175 – Fairgrounds and
Amusement Parks: Guidance on Safe
Practice. The document is the result of
work carried out by the Fairgrounds
and Amusement Parks Joint Advisory
Committee (FJAC) which has worked
for over 25 years to continually
improve standards and the exchange of
information. Fairgrounds and
amusement parks have been shown to
be relatively safe compared to such
activities as driving a car or riding a
bicycle but there have been a small
number of serious accidents involving
the general public and employees.
IET Wiring Matters | Winter 07 | www.theiet.org
Amusement devices
The Scope of Section 740 does not
cover amusement devices but, in law,
there is still a requirement to ensure
that the devices are fit for use.
The Amusement Device Safety
Council (ADSC) is the policy making
body for safety, self regulation and
technical guidance in the UK
amusement industry. This committee,
in partnership with HSE, develops
the policy for, and oversees the
Amusement Device Inspection
Procedures Scheme (ADIPS). ADIPS is
the fairground and amusement park
industry’s self regulated safety
inspection scheme which registers
competent ride inspectors and the
rides they inspect.
The purpose of the scheme is to
promote and improve fairground and
amusement park safety through rules
and procedures relating to the annual
inspection of the amusement devices.
It is supported by industry
associations who require that their
members use ADIPS.
ADIPS is also available to any
operator of amusement devices as it
demonstrates ‘best practice’ and their
compliance with the Health and Safety
at Work (etc) Act.
Further information
The following standards and
publications have been referenced in
this article or will provide further
reading on the subject:
BS 1363 – 13 A plugs, socket-outlets and adaptors
BS 7919 – Electric cables. Flexible cables rated up
to 450/750V, for use with appliances and
equipment intended for industrial and similar
environments
BS EN 50085 – Cable trunking and cable ducting
systems for electrical installations
BS EN 60204-1 – Safety of machinery. Electrical
equipment of machines. Specification for general
requirements
BS EN 60309-1 – Plugs, socket-outlets and
couplers for industrial purposes. General
requirements
BS EN 60309-2 - Plugs, socket-outlets and
couplers for industrial purposes. Dimensional
interchangeability requirements for pin and
contact-tube accessories
BS EN 60332-1-2 – Tests on electric and optical
fibre cables under fire conditions. Test for vertical
flame propagation for a single insulated wire or
cable. Procedure for 1 kW pre-mixed flame
BS EN 60947-2 – Low-voltage switchgear and
control gear. Circuit-breakers
BS EN 61008-1 – Residual current operated
circuit-breakers without integral overcurrent
protection for household and similar uses (RCCBs).
General rules
BS EN 61009-1 – Residual current operated circuitbreakers with integral overcurrent protection for
household and similar uses (RCBOs). General rules
BS EN 61347-2-2 – Lamp controlgear. Particular
requirements for d.c or a.c. supplied electronic
step-down convertors for filament lamps
BS EN 61386 – Conduit systems for cable
management. General requirements
BS EN 61537 – Cable management. Cable tray
systems and cable ladder systems
BS EN 61558-2-6 – Safety of power transformers,
power supply units and similar. Particular
requirements for safety isolating transformers for
general use
IEC/HD 60364-7-740 – Electrical installations of
buildings – Part 7-740: Requirements for special
installations or locations – Temporary electrical
installations for structures, amusement devices and
booths at fairgrounds, amusement parks and circuses
HSG 175 – Fairgrounds and Amusement Parks:
Guidance on Safe Practice ISBN 978-0-7176-6249-4
ADIPS – www.adips.co.uk
Thanks to Ken Morton of the HSE. PV POWER
SUPPLY SYSTEMS
12
SOLAR PHOTOVOLTAIC POWER
SUPPLY SYSTEMS
by John Ware
IT IS PLANNED for BS 7671:2008
to include a new Section 712 providing
additional requirements for safety
applicable to solar photovoltaic (pv)
power supply systems. The additional
requirements planned for inclusion in
BS 7671:2008 along with some
explanations are discussed in this
article. As with any low voltage
installation, the general requirements
in Parts 1 to 6 of BS 7671:2008 have also
to be met which include in Part 5,
Section 551, requirements for low
voltage generating sets.
Please note that a list of definitions
is included at the end of this article.
The risks
The particular risks associated with
solar photovoltaic systems are:
PV systems cannot be switched off.
Modules produce electricity when
exposed to daylight. Hence, unlike
most other electrical installation
work, the installation of a PV
system typically involves working on
a live system. Regulation 14 of the
Electricity at Work Regulations
gives requirements that must be
met. Special precautions should be
made to ensure live terminals are
either not accessible or cannot be
readily touched during installation
and maintenance. Such terminals
will be live at all times during
daylight hours. It is important that
anyone opening an enclosure is
aware of this.
An electrician who has come to
work on the electrical installation
needs to be aware that there is a
second source of energy which will
also need to be isolated.
IET Wiring Matters | Winter 07 | www.theiet.org
PV modules are current-limiting
devices which require a nonstandard approach when designing
fault protection systems for the dc
side, as fuses are not likely to
operate under short-circuit
conditions. A different approach to
fault protection is often needed,
such as sizing the conductors for the
maximum fault current that can
flow at any given point in the
circuit.
PV systems include dc wiring, with
which few electrical installers are
familiar.
PV presents a unique combination
of hazards – due to risk of electric
shock, falling and simultaneous
manual handling difficulties. All of
these hazards are encountered as a
matter of course on a building site,
but rarely all at once. While roofers
may be accustomed to minimising
risks of falling or injury due to
manual handling problems, they
may not be used to dealing with
the risk of electric shock. Similarly,
electricians would be familiar
with electric shock hazards but not
with handling large objects at
heights.
The particular requirements of
Section 712 of BS 7671:2008 apply to
electrical installations of PV power
supply systems which will only work
when connected in parallel with an
electricity supply. The requirements in
this section are not intended for
PV systems for standalone operation.
The requirements are for PV
systems assembled from items of
equipment, not supplied as a
complete unit.
PV modules
junction box
DC side
AC side
inverter
meter
consumer
unit
Figure 1: Block diagram of a PV system
The Electricity Safety, Quality and
Continuity Regulations 2002
A solar photovoltaic (PV) power supply
systems described in Section 712 is
required to meet the requirements of
the Electricity Safety, Quality and
Continuity Regulations 2002 as it is
an embedded generator. Where the
output does not exceed 16 A per phase
the PV system is considered as a
small-scale embedded generator
(SSEG) that is exempted from certain
of the requirements provided that:
the equipment should be type 왘
PV POWER
SUPPLY SYSTEMS
14
tested and approved by a
recognised body,
the consumer’s installation should
comply with the requirements of
BS 7671,
the equipment must disconnect
itself from the distributor’s network
in the event of a network fault, and
the distributor must be advised of
the installation before or at the time
of commissioning.
Connection of a PV system to the
electrical installation
A PV system used as an additional
source of supply in parallel with
another source should preferably be
connected on the supply side of all the
protective devices for the final circuits
of the installation. If a PV system is to
be connected on the load side of all the
protective devices for a final circuit of
the installation additional
requirements given in Regulation 551.7
of BS 7671: 2008 must be met.
PROTECTION FOR SAFETY
Protection against electric shock
PV equipment on the dc side must be
considered energized, even when the
system is disconnected from the ac
side.
Protection by the use of Class II or
equivalent insulation should
preferably be adopted on the dc side.
Protection by non-conducting location
or earth-free local equipotential
bonding is not permitted on the
dc side.
On the ac side, the PV supply cable
should be connected to the supply side
of the protective device for automatic
disconnection of circuits supplying
current-using equipment.
Where an electrical installation
includes a PV power supply system
without at least simple separation
between the ac side and the dc side, an
RCD installed to provide fault
protection by automatic disconnection
IET Wiring Matters | Winter 07 | www.theiet.org
string
cables
N strings
(connected in
parallel)
main
DC cable
M modules per string (connected in series)
Figure 2: Simplified circuit of dc side
of supply should be type B. B type
residual current circuit-breakers
provide specific protection of single
and three-phase installations and
people even in the presence of dc fault
currents on the network generated by
controllers and variable speed drives,
battery chargers and inverters and
power supplies
They are a requirement for single
and three-phase supplied applications,
where Class l equipment installed
downstream from the RCCB is likely
to produce dc component fault
currents (pure dc fault). Type B RCDs
also provide protection against
sinusoidal ac residual currents (AC
type) and pulsed dc residual currents
(A type).
However, where the PV convertor is,
by construction, not able to feed dc
fault currents into the electrical
installation, a type B RCD is not
needed.
Protection by extra-low voltage:
SELV and PELV
For SELV and PELV systems, UOC STC
replaces Uo and must not exceed
120 V dc
Protection against overload
on the dc side
Overload protection may be omitted to
PV string and PV array cables when
the continuous current-carrying
capacity of the cables is equal to or
greater than 1.25 times ISC STC at any
location. Overload protection may be
omitted to PV main cables when the
continuous current-carrying capacity
of the PV main cable is equal to or
greater than 1.25 times ISC STC of the
PV generator.
Protection against short-circuit
current
The PV supply cable must be protected
against short-circuit current by an
overcurrent protective device
installed at the connection to the ac
mains.
Isolation and switching
To allow maintenance of the PV
converter, means of isolating the PV
converter from the ac side and the dc
side must be provided.
ac side. Means of isolation should be
provided on the ac side. A switchdisconnector should be installed
adjacent to the inverter. The device
should switch all live conductors and
should be able to be locked off. A
further means of isolation should be
provided at the consumer unit or
distribution board. At the point of
installation of any ac isolator, the
public supply should be considered as
the source and the PV system should
be considered as the load.
PV POWER
SUPPLY SYSTEMS
15
dc side. A switch disconnector must be
provided on the dc side of the PV
converter. The dc switch should switch
all live conductors and must be suitably
rated for the required dc operation.
Switching ac is less demanding than
switching dc – with an ac supply, the
voltage passes through 0 V many times a
second. A switch planned to be used on
the dc side must be rated to break dc; an
equivalent ac-rated switch is not
acceptable or safe.
dc connectors. Connectors, where used
to connect PV modules, PV strings or
the inverter should be dc rated and
touch safe (i.e. the IP rating should be
not less than IP21). They should be of
Class II design, shrouded and of a
design totally dissimilar in appearance
to any other connectors used in the
installation.
Selection and erection
PV modules should comply with the
requirements of the relevant
equipment standard, e.g. BS EN 61215
for crystalline PV modules. PV
modules of class II construction or
with equivalent insulation are
recommended if UOC STC of the PV
strings exceeds 120 V dc The PV array
junction box, PV generator junction
box and switchgear assemblies should
comply with BS EN 60439-1.
Electrical equipment on the dc side
must be suitable for direct voltage and
direct current.
PV modules may be connected in
series up to the maximum allowed
operating voltage of the PV modules
(UOC STC of the PV strings) and the PV
converter, whichever is lower.
Specifications for this equipment shall
be obtained from the equipment
manufacturer.
If blocking diodes are used, their
reverse voltage shall be rated for 2 x
UOC STC of the PV string. The blocking
diodes shall be connected in series
with the PV strings.
As specified by the manufacturer,
the PV modules should be installed in
such a way that there is adequate
heat dissipation under conditions
of maximum solar radiation for
the site.
Cables routed behind a PV array
should be rated for a temperature of
at least 80°C. Cable should be installed
so as to minimise the risk or earth
faults and short circuits. Cables
should be sized such theat the
voltage drop between the array and
inverter is less than 3 per cent.
External cables 왘
for skills
wred
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of the IEE Wiring Regulations (BS7671:2008)
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our flexible qualifications provide a recognised mark of
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IET Wiring Matters | Winter 07 | www.theiet.org
PV POWER
SUPPLY SYSTEMS
16
Distribution board
4
Overcurrent
protective device
(712.434.1)
3
PEN/PE
Main equipotential bonding bar
supply point
Protective equipotential bonding,
if relevant
Metering as required
Circuits supplying currentusing equipment
PV generator
Bypass diodes,
if relevant
AC side
DC side
I
PV string
Blocking
diode, if
relevant
(712.512.1.1)
PV supply cable
switchgear assembly
Devices for isolation
(712.537.2.1.1 and 712.537.2.2.5)
PV DC main cable
L+
RCD,
if relevant
PV invertor
Transformer,
if relevant
DC
L-
PV module
AC
Device for isolation
(712.537.2.2)
U
Common enclosure (optional)
Overvoltage protective device,
if relevant
PV generator junction box
PV string cable
Overcurrent protective device, if necessary
Figure 3: PV system – general schematic, one array
should be UV stable, water resistant
and flexible. For the dc system, it is
recommended that Class II equivalent
wiring, connections and equipment is
used wherever possible as this will
reduce fire risk.
PV string cables, PV array cables
and PV dc main cables must be
selected and erected so as to minimise
the risk of earth faults and shortcircuits. This may be achieved for
example by reinforcing the protection
of the wiring against external
influences by the use of single-core
sheathed cables.
The cable connecting the inverter to
the consumer unit or distribution
board must, as for any circuit, have
overcurrent protection which includes
both overload and fault protection.
Accessibility. The selection and
erection of equipment shall facilitate
safe maintenance and shall not
adversely affect provisions made by
the manufacturer of the PV equipment
to enable maintenance or service work
to be carried out safely.
The inverter should carry a current
Engineering Recommendation G77/1
Earthing arrangements and
protective conductors
IET Wiring Matters | Winter 07 | www.theiet.org
type test certificate. A key requirement
is that the inverter will disconnect the
PV system when the distribution
system is not energised. This is to
prevent the hazardous situation of the
photovoltaic system feeding the
network or local distribution system
during a planned or unscheduled loss
of mains. Such an event is termed
‘islanding’ and presents a potential
danger to those working on the
network/distribution system.
Where protective equipotential
bonding conductors are installed, they
shall be parallel to and in as close
contact as possible with dc cables and
ac cables and accessories.
Lightning protection system
Where there is a perceived increase in
risk of lightning strike as a
consequence of the installation of a
PV system advice should be taken
from a lightning protection system
specialist as to whether a separate
lightning protection system should be
installed. Additionally, if the PV array
has a metal frame which is not
required to be earthed because it is of
Class II construction, advice should be
taken as to whether it should in fact be
connected to the Main Earthing
Terminal when considering lightning
protection implications. Where a
lightning protection system is already
PV POWER
SUPPLY SYSTEMS
17
Figure 4: PV system – general schematic with more than one array
present, it is considered best practice
to main bond the array frame to the
Main Earthing terminal.
Where an LPS is installed or is to be
installed, PV system components
should be mounted away from
lightning rods and down leads. Long
leads, for example dc main cables
connecting the array to the inverter
that are over 50m in length, should be
installed in earthed metal conduit or
trunking.
To minimize voltages induced by
lightning which could result in
electromagnetic interference, the area
of all wiring loops should be kept as
small as possible.
LABELLING
Junction boxes. All junction boxes (PV
generator and PV array boxes) must
carry a warning label indicating that
parts inside the boxes may still be live
even after isolation from the PV
converter.
The dc isolator should be labelled as
‘PV array dc isolator’, with the ON and
OFF positions clearly marked. Switch
enclosures should also be labelled with
‘Danger, contains live parts during
daylight’.
The ac isolator should be labelled as
‘PV system isolator’ with the ON and
OFF positions clearly marked.
from the origin
At the consumer unit or
distribution board to which the
generating set is connected
At all points of isolation of both
sources of supply.
The warning notice should have the
following wording:
_____________________________________
WARNING - DUAL SUPPLY
Additional source. As the installation
includes a generating set, the PV
system, which is used as an additional
source of supply in parallel with
another source, and warning notices
should be affixed at the following
locations in the installation:
Isolate the mains supply at.....................
Isolate the generator at...........................
_____________________________________
At the origin of the installation
At the meter position, if remote
All labels shall be clear, easily
visible, constructed and affixed to 왘
Isolate both mains and on-site
generation before carrying out work.
IET Wiring Matters | Winter 07 | www.theiet.org
PV POWER
SUPPLY SYSTEMS
20
last and remain legible for the life of
the installation.
Parallel operation
Further requirements with regard to a
PV installation operating in parallel
with the public supply system are
given in Regulation 551.7 of BS 7671.
Definitions, and explanations
PV – Solar photovoltaic.
PV cell – Basic PV device which can
generate electricity when exposed to
light such as solar radiation.
A photovoltaic cell acts as a current
source, hence PV modules are current
limiting devices – even under short
circuit conditions, the output current
of a module will not rise above a
certain level (Isc). Operating a module
in short circuit is in general of little
consequence, indeed many charge
controllers in battery charging
systems routinely short circuit an
array output.
PV module – Smallest completely
environmentally protected assembly of
interconnected PV cells.
Some modules have an electrical
output that is considerably higher
during the first weeks of operation.
This increase is on top of that
produced by temperature/irradiance
variation. Typically, operation during
this period will take Voc, Isc (and
nominal power output) well above any
value calculated using a standard
multiplication factor. To avoid
oversizing for this eventuality the
array could be left disconnected for
that initial period. Refer to the
manufacturer for this information.
PV string – Circuit in which PV
modules are connected in series, in
order for a PV array to generate the
required output voltage.
PV module string circuits cannot
rely on conventional fuse protection
for automatic disconnection of supply
under fault conditions. This is because
the short circuit current is little more
than the operating current – a fuse
would simply not operate.
IET Wiring Matters | Winter 07 | www.theiet.org
Figure 5: PV system
PV array – Mechanically and
electrically integrated assembly of PV
modules, and other necessary
components, to form a dc power supply
unit.
PV array junction box – Enclosure
where all PV strings of any PV array
are electrically connected and where
protection devices can be located if
necessary.
PV generator – Assembly of PV arrays.
PV generator junction box – Enclosure
where all PV arrays are electrically
connected and where devices can be
located if necessary.
PV string cable – Cable connecting PV
modules to form a PV string.
PV array cable – Output cable of a PV
array.
PV dc main cable – Cable connecting
the PV generator junction box to the
dc terminals of the PV inverter.
PV inverter – Device which converts dc
voltage and dc current into ac voltage
and ac current.
PV supply cable – Cable connecting the
ac terminals of the PV inverter to a
distribution circuit of the electrical
installation.
PV ac module – Integrated module/
invertor assembly where the electrical
interface terminals are ac only. No
access is provided to the dc side.
PV installation – Erected equipment of
a PV power supply system.
Standard test conditions (STC) Test
conditions specified in IEC 60904-3 for
PV cells and modules.
Open-circuit voltage under standard
test conditions UOC STC Voltage under
standard test conditions across an
unloaded (open) generator, or on the dc
side of the convertor.
Short-circuit current under standard
test conditions ISC STC Short-circuit
current of a PV module, PV string, PV
array or PV generator under standard
test conditions.
dc side Part of a PV installation from
a PV cell to the dc terminals of the PV
inverter.
ac side Part of a PV installation from
the ac terminals of the PV inverter to
the point of connection of the PV
supply cable to the electrical
installation.
Simple separation Separation
provided between circuits or between
a circuit and earth by means of basic
insulation. CPC currents
23
Protective conductor current. Electric
current which flows in a protective
conductor under normal operating
conditions.
PROTECTIVE
CONDUCTOR
CURRENTS
by Stewart Langdown of TridonicAtco UK Ltd
FLUORESCENT LIGHTING
or other discharge lighting often
incorporates electronic high frequency
control gear which provides many
advantages, including:
energy saving
ability to provide dimming,
lower weight
increased lamp life
reduction or elimination of
stroboscopic effects
instant start
A consequence of the use of such
control gear is that often electrical
filters have to be provided to suppress
high frequency noise being
superimposed on the mains supply.
These filters generally consist of
series-connected inductors in each live
conductor with capacitors connected
between the live conductors and the
circuit protective conductor. The
small filter capacitors connected
between the live conductors and the
circuit protective conductor result in a
small but non-negligible, protective
conductor current. Where a large
installation incorporates many
luminaires, such as a large office
block, the resultant protective
conductor current, in the earthing
conductor for the installation, can
add up to a few amperes.
Protective conductor currents can
also result from the mains input filters
associated with switch-mode powersupplies of IT equipment and other
equipment such as photocopiers, fax
machines and motorised equipment
employing variable speed drives. See
figure 1.
IEC 598 gives the maximum value
for leakage current as < 0.5 mA for
Class 0 and II and 1 mA for Class I
luminaires.
Definitions
The current flowing in the protective
conductor is often referred to as
‘Earth leakage current’. The definition
of protective conductor current,
from Part 2 of the 16th Edition of
BS 7671, is:
The term Earth Leakage current is
no longer defined.
Interestingly, in the 17th Edition of
BS 7671, it is planned that protective
conductor current will be defined as:
Protective conductor current. Electric
current appearing in a protective
conductor such as leakage current or
electric current resulting from an
insulation fault.
The definition planned for the 17th
Edition represents a clarification, in
that both continuous protective
conductor current due to normal
operation and occasional protective
conductor current due to faults are
recognized.
Protective conductor current is
generally thought of as the difference
of the currents flowing in the line and
neutral conductors. Typically this is
between the current carrying
conductors and the case or frame of
the electrical device, which is almost
inevitably connected to earth.
However protective conductor
current may result from currents
flowing in interconnecting cables, such
as the outer screen of signal cables,
that are connected between different 왘
Figure 1: A typical filter circuit which includes series connected inductors, bypass capacitors and
resistors to discharge the capacitors
IET Wiring Matters | Winter 07 | www.theiet.org
CPC currents
24
왗 items of electrical equipment. See
figure 2. The leakage current need not
flow via the protective or functional
earth. Signal cables coupled to the
frame or casing can provide additional
routes for protective conductor
current flow.
There is a risk of electric shock if a
protective conductor becomes
disconnected because where the circuit
supplies Class I equipment under earth
fault conditions there will be no path
for the fault current to flow to earth
causing operation of the protective
device. In addition, the metal case of
the item of equipment is likely to
remain at an elevated potential
presenting a latent risk of shock for
someone contacting the case and an
item of earthed metalwork, such as a
metallic water pipe. Furthermore,
where an item of equipment has a
protective conductor current, should
there be a break in the protective
conductor, the metal case of the item of
equipment will attain an elevated
potential posing a risk of electric shock.
This shock risk is extended to all the
items of equipment on the particular
circuit, whether they individually
have high protective conductor
currents or not.
RCD operation. Equipment causing
protective conductor currents
connected downstream of a residual
current device (RCD) can affect the
operation of the device.
An RCD operates by monitoring the
difference between the line and
neutral conductor currents and, when
the difference – which represents the
earth leakage current – exceeds a
predetermined limit, it will operate
and disconnect the circuit.
The RCD detects the difference
between phase and neutral conductor
currents. The difference in the
currents may be due to a fault or due
to filters in the equipment supplied.
The RCD is generally installed for the
purpose of detecting an earth fault,
providing the circuit is properly
IET Wiring Matters | Winter 07 | www.theiet.org
equipment
RCD
interconnected
equipment
filter
fault
protective conductor
current due to filter
protective conductor
current due to a fault
protective conductor current
due to interconnected equipment
Figure 2: Protective conductor currents resulting from a filter, a fault or interconnecting cables.
Figure 3: RCD operation
under fault conditions. The
RCD monitors the
difference between phase
and neutral currents which
represents the fault
current. The fault current
flows in the protective
conductor circuit. When
this fault current exceeds
a predetermined limit, the
RCD operates and
disconnects the circuit.
designed, as the current resulting from
a fault is generally significantly higher
than other protective conductor
currents.
Design considerations. An installation
containing a number of luminaires
with electronic switchgear, IT
equipment or interconnected
equipment can be a cause for concern
where RCD protection is required for
the respective final circuits.
The installation designer must
ensure that the protective conductor
current seen by the RCD in normal,
fault-free, operation is kept
significantly less than that at which
the device will operate.
Where it is necessary to specify a
residual current device with a residual
operating current of 30 mA in order to
meet the requirement for additional
protection, such as in a socket-outlet
circuit, then in order to keep the
expected protective conductor currents
well below the residual operating
current it may be necessary to replace
the proposed single circuit by separate
circuits each with its own RCD.
Less serious, but equally frustrating,
is the effect uncontrolled residual
current may have on sensitive
equipment which could fail, give false
information readings or suffer from
noise problems; this could be critical
in medical applications.
Technology as we have discussed in
this brief article has bought many
benefits but as we move to a greener,
more sustainable lighting market then
adequate provisions must be made by
the electrical designers and installers
to give sufficient provision to the
potential issues raised by the user of
new technology in commercial and
residential properties.