Specification of electrical works
Cubicle panels
Main and distribution switchboards as listed in the schedules shall be purpose-made and
shall consist of a sheet-steel cubicle designed for access from front only or from front and
rear according to site position, containing distribution busbars, all cable terminations and
interconnections. All items. of switch and fusegear are to be flush-mounted on the front
of the cubicle which is to be finished grey stoved enamel.
Switchboards shall be suitable for controlling reduced voltage supplies and shall be
comprehensively tested before dispatch from the manufacturer’s works to ensure
satisfactory operation of all component parts. The tests shall include continuity and 2kV
flash tests. Busbar systems in switchboard shall be tested at 50kA for 1s.
Full protection shall be provided by means of mechanical interlocks with the covers
and operating levers, The switchboard shall have an earthing terminal and earthing bar.
External connections shall be provided to allow all outgoing cables to terminate at
either top or bottom of the switchboard.
Busbars
Busbar panels as shown on the drawings and listed in the schedules are to be of the
ratings indicated and are to be of high-conductivity copper mounted on robust vitreous
porcelain insulators complete with all necessary clamps. The busbars are to be enclosed
in a stove-enamelled sheet-steel casing with cast-iron frame members and detachable top,
bottom and side plates. The covers are to be of the screw-on type. The panels are to be
provided with all necessary holes and bushes for incoming and outgoing cables.
Incoming and outgoing switch fuses of the types and ratings shown on the drawings
and schedules shall be provided and installed adjacent to the busbar chamber. All
necessary interconnections between switch fuses and busbars shall be made and all the
equipment shall be fixed on a common angle-iron frame which is to be supplied as part of
the electrical contract. The frame is to be painted one coat primer and two coats grey
finish.
Where necessary, trunking shall be supplied and installed from busbars to meter
positions.
Fuse switches
Fuse switches shall be heavy-duty pattern fitted with HRC fuse links. They shall have
heavy-gauge steel enclosures with cast-iron frame members, rust-protected and finished
grey stoved enamel. Front access doors shall be fitted with dust-excluding gaskets and
shall be interlocked so that they cannot be opened when the switch is ‘on’. Operating
handles shall be lockable in both the on and off positions. The top and bottom endplates
shall be removable.
Each fuse switch shall be supplied complete with the correct HRC fuse links.
Each fuse switch shall have flag on-off indication.
Design example 291
Fuse switches shall be 500V rating and shall be clearly marked with their current
rating, and the items of equipment that they serve.
Switch fuses
Switch fuses shall be industrial pattern dust-proof type with HRC fuse links. They shall
have enclosures fabricated from sheet steel finished grey stoved enamel with removable
top and bottom endplates and shall have doors fitted with dust-proof gaskets. They shall
have front-operated handles with visible on-off indication.
The interiors shall have vitreous porcelain bases fitted with plated non-ferrous
conducting components. Switches shall be of the quick make-and-break type and have
removable shields over the fixed contacts and removable moving contact bars.
Each switch fuse shall be supplied complete with the correct HRC fuse links.
Switch fuses shall be 500V rating and shall be clearly marked with their current rating,
and the items of equipment that they serve.
Isolators
Isolators shall be heavy-duty pattern with steel enclosures having cast-iron frame
members, rust-protected and finished grey stoved enamel. Front access doors shall be
fitted with dust-excluding gaskets and shall be interlocked so that they cannot be opened
when the switch is ‘on’. Operating handles shall be lockable in both the on and off
positions and shall have visible on-off indication.
Isolators shall be 500V rating and shall be clearly marked with their current rating.
The moving contact assemblies are to be removable for inspection and maintenance.
Distribution boards
All distribution boards shall be single-pole or triple-pole with neutral bar, and with
fuseways/CBs 20 or 30A or above as specified.
All distribution boards shall be of the surface pattern in heavy sheet-steel cases of the
500V range with HRC fuse carriers.
On all triple-pole and neutral distribution boards the number of neutral terminals to be
provided shall be the same as the total number of fuse-ways/CBs in the board. This
information must be given to the manufacturers when ordering, together with information
with regard to composite boards having a multiplicity of fuse ratings as specified.
In the case of flush installations, the distribution boards shall be mounted over flush
adaptable iron boxes into which the conduits and wiring of the system will terminate. The
boxes shall be of a size to be agreed on site with the consulting engineer.
Doors of all distribution boards shall be lockable either by means of a barrel-type lock
with detachable key or by means of a modified door-fixing screw, bracket and padlock.
Ample clearance shall be provided between ‘live’ parts and the sheet-steel protection
to allow cables to be brought to their respective terminals in a neat and workmanlike
manner.
To separate opposite poles a fillet of hard incombustible insulating material shall be
provided of sufficient depth to reach the inside of the door.
Design of electrical services for buildings 292
In each distribution board spare fuse carriers shall be provided and held in place by a
suitable clip so that the carrier cannot be inadvertently dislodged.
Distribution boards shall be fixed at a height to give easy access, and be provided with
a schedule complying with 514–09–01 of BS 7671.
Starters
A starter shall be provided for each motor as indicated on the drawings and schedules.
The starters shall be surface-mounted with a sheet-steel case containing a triple-pole
contactor with vertical double break per pole having silver-faced contacts. They are to
have continuously rated operating coils with inherent undervoltage release. Operating
coils are to be supplied from phase to neutral. The starters shall have magnetic-type
overload relays with adjustable oil dashpot time lags and stop/reset push-buttons in the
front cover. The cover is also to contain the start push-button.
Starters are to have single-pole auxiliary switches and shall incorporate single-phase
protection.
Star-delta starters shall have a time-delay device complete with all main and control
wiring and terminal block for incoming and outgoing cables. The time-delay device shall
be of the pneumatic pattern with an instantaneous reset allowing restarting immediately
after a star-delta switching operation. The star and delta contactors are to be mechanically
and electrically interlocked.
The overload relays are to be correctly set to ensure adequate protection without
nuisance tripping.
Steel conduit
All steel Class ‘B’ conduits and conduit fittings throughout the whole of this installation
shall comply in all respects with British Standard Specification BS 31:1940. All PVC
insulated cables, other than flexibles, shall be protected throughout their length with
heavy-gauge screwed welded conduit (enamelled or galvanized as required) with the
necessary malleable iron loop-in, draw-in, angle and outlet boxes. No type of ‘elbow’ or
‘tee’ will be allowed on works under this Specification.
Where adaptable boxes are used they shall be of cast iron or heavy-gauge sheet steel
of not less than 12-gauge.
No conduit of less than 20mm diameter shall be used.
A solid coupling shall be inserted in every flush conduit run at the point where it
leaves a ceiling, wall or floor for ease of dismantling if required.
Except where otherwise stated conduit is to be finished black enamel.
No conduit shall be installed with more than two right-angle bends without draw-in
boxes and draw-in boxes shall not be more than 8m apart.
All conduits, except where otherwise specified, shall drop not rise to the respective
points. In no circumstances shall the conduit be erected in such a manner as to form a U
without outlet, or in any other way that would provide a trap for condensed moisture.
Provision shall be made for draining all conduits or fixtures by a method approved by
the consulting engineer.
Design example 293
No ceiling looping-in point box shall be used as a draw-in box for any other circuit
than that for which such point box is intended.
Ceiling point boxes are to be of medium pattern malleable iron, with fixing holes at
50mm centres and conforming to BS Specification.
Flush ceiling point boxes which do not finish flush with the finished surface of the
ceiling, etc., shall be fitted with malleable iron extension rings.
Horizontal or diagonal runs of flush conduit on structural or partition walls will not be
permitted. All flush conduits shall drop or rise vertically to their respective points.
Connections between conduits and trunking and conduit and steel boxes, or between
conduit and steel cases of distribution gear or equipment, shall be made by means of a
flanged coupling and brass smooth-bore entry bush. The lead washer shall be fitted on the
inside of the trunking or box, etc.
All lids for draw-in boxes, etc., whether of the BS or adaptable type, shall be of heavy
cast-iron or 12-gauge sheet steel, and shall be fixed (overlapping for flush work) by
means of two or four M6 round-headed brass screws as required.
Conduits set through walls will not be permitted. When change of direction is required
after passing through a wall an appropriate back outlet box is to be fitted.
All joints between lengths of conduit, or between conduit and fittings, etc., are to be
threaded home and butted.
Sets and bends are to be made without indentation, and the bore must be full and free
throughout. All screw-cutting oil must be carefully wiped off before joining up.
Conduit runs, as far as possible, are to be symmetrical and equally spaced.
The electrical contractor must take all precautions in situations likely to be damp to
see that all conduits and boxes in the vicinity are rendered watertight.
During the progress of the work all exposed ends of conduits shall be fitted with
suitable plastic or metal plugs. Plugs of wood, paper and the like will not be acceptable as
sufficient protection.
Lighting, heating, power and any other types of circuit shall be run in separate
conduits and no circuit of any one system shall be installed in any conduit or box of any
other system.
The proposed runs shall be submitted to the consulting engineer for approval before
work is commenced.
Conduit fittings
All conduit fittings shall be of malleable iron which shall conform to the British
Standards Specification BS 31:1940.
All fittings shall be of the screwed pattern, and no solid or inspection elbows, tees or
bends shall be installed. Generally, all conduit fittings shall be stove-enamelled black or
other approved finish inside and out, but where galvanized conduit is installed, all fittings
shall be galvanized by the hot process both inside and out. Such fittings shall be of Class
B pattern.
All conduit fittings not carrying lighting or other fittings shall be supplied with
suitable cast-iron covers with round-head brass screws. Where flush boxes are installed
the covers shall be of the overlapping rustproof pattern.
Design of electrical services for buildings 294
All ceiling point boxes, except in the case of surface conduits, shall finish flush with
the underside of the ceiling, extension rings being used where necessary.
Every flush ceiling point box to which a luminaire is to be attached shall be fitted with
a break-joint ring of approved type.
Where surface conduit is used in conjunction with distance saddles, special boxes shall
be used, to obviate the setting of conduit when it enters or leaves the boxes.
All conduit boxes, including boxes on and in which fittings, switches and socket
outlets are mounted, shall be securely fixed to the walls and ceilings by means of not less
than two countersunk screws, correctly spaced, and the fixing holes shall be countersunk,
so that the screw heads do not project into the box.
Flexible conduit
Connections to individual motors and heating equipment run in conduit shall be made
using a minimum of 300mm of watertight flexible conduit. The conduit shall be Kopex
LS/2.
Flexible conduit connecting to heating equipment shall employ butyl rubber insulated
CSP sheathed cables and suitable terminal blocks shall be used in all boxes where a
change in cable type is involved.
Earth continuity of all flexible conduits shall be maintained by 4mm2 minimum copper
conductors forming one of the cores of the cable.
Flexible conduits shall be terminated with the Kopex couplings and connectors
specially made for the purpose.
Cable trunking
Cable trunking shall be supplied and installed complete with fittings and accessories and
shall be of an approved manufacture. It shall be manufactured from zinc or lead-coated
sheet steel finished stove enamelled grey or galvanized and shall be of 18swg for sizes up
to and including 75mm×75mm section and 16swg for sizes above.
All bends, tees, reducers, couplings, etc., shall be of standard pattern: where it is
necessary for a special fitment to be used, it is to be fabricated by the manufacturers.
Where it is necessary to provide additional trunking over fixings, these shall be
supplied by the manufacturer and shall be applied with the manufacturer’s special tools.
Where holes or apertures are formed in the trunking for cable entry, they shall be
bushed with brass smooth-bore entry bushes, or PVC grommet strips. Cable supports are
to be inserted in vertical runs of trunking and cables are to be laced thereto in their
respective groups.
Fire barriers of hard insulating material shall be provided in vertical runs of trunking
where they pass through floors.
Where more than one service is involved multi-compartment trunking shall be
employed to separate the services.
Cable tray
Design example 295
Cable tray is to be made of 16-gauge perforated mild-steel sheet and is to be complete
with all coupling pieces and bends, offsets and fixing brackets, to enable the tray to fit the
structure accurately.
Where cables are taken over the edge of the tray they shall be protected by rubber
grommets.
MICC cable
Mineral-insulated metal-sheathed cables shall be high-conducting copper conductors
embedded in magnesium oxide and sheathed with copper with an overall covering of
PVC.
All cable terminations shall be protected and sealed with ring-type glands with screwon
pot-type seals utilizing cold plastic compound and neoprene sleeving all of an
approved pattern, and applied with the special tools recommended by the cable
manufacturers.
Cold screw-on pot-type seals shall be used except where the ambient temperature in
which the cable will operate will exceed 170°F, where the hot-type seal shall be used.
Four-core MICC cables shall not be used for ring circuits.
Vibration-absorbing loops shall be formed in MICC cables connected to motors and
other vibrating equipment.
Connections and joints in MICC cables shall only be made at the terminals of
switches, ceiling roses, or at connector blocks housed in outlet boxes. Connector blocks
shall have a minimum of two screws per conductor.
Where entry is made into equipment which does not have a spouted entry, the cable
shall be made off by means of coupling, male bush, and compression washer.
MICC cables shall be neatly installed and shall be clipped by means of copper saddles
secured by two brass screws. Where two, three or four cables are run together multiple
saddles shall be used.
MICC cables shall be delivered to the site with the manufacturers’ seals and
identification labels intact and shall be installed in accordance with the manufacturers’
recommendations and using the specialized tools recommended by the manufacturer.
They shall be tested when installed before being sealed and again at the end of the
contract.
They shall be sealed against the ingress of moisture at all times during the contract.
PVC cable
Cable PVC-insulated only, and PVC-insulated PVC-sheathed cable shall be 600/1000V
grade to BS 6004:1969.
The cable shall be delivered to site on reels, with seals and labels intact and shall be of
one manufacturer throughout the installation.
The cable shall be installed direct from the reels and any cable which has become
kinked, twisted or damaged in any way shall be rejected. The installation shall be cabled
on the loop-in system, i.e. wiring shall terminate at definite points (switch positions,
lighting points, etc.) and no intermediate connections or joints will be permitted. Cables
shall not pass through or terminate in lighting fittings.
Design of electrical services for buildings 296
Where it is necessary to make direct connection between the hard wiring and flexible
cord, this shall be done by means of porcelain-shielded connectors with twin screws. No
luminaire shall be connected directly to the hard wiring.
The terminations shall be suitable for the type of terminal provided and shall be either
sweated lugs of appropriate size, or eyelet or crimped type cable terminations, all of
reputable manufacture. Shakeproof washers shall be used where electric motors are
connected.
Where cable cores are larger than terminal holes, the cables shall be fitted with
thimbles. For all single connections, they shall be doubled or twisted back on themselves
and pinching screws shall not be permitted to cut the conductors. Cables shall be firmly
twisted together before the connection is made.
In no circumstances shall cables be trapped under plain washers as a termination.
Cables shall be coloured in accordance with IEE Regulations BS 7671.
Only two cables shall generally be bunched together at one terminal. In exceptional
cases three cables may be bunched together at one terminal with the authority of the
engineer given on site.
Flexible cords
All flexible cords shall comply with British Standard Specification BS 6500:1969, and
shall consist of high-conductivity tinned copper conductors of the required crosssectional
area insulated and sheathed as detailed hereunder:
Lighting pendants
Two-core 0.75mm2 heat-resisting circular flexible cord EP rubber-insulated CSPsheathed.
Colour of sheath, white.
Heating apparatus and equipment requiring flexible cable connection
Heat-resisting circular flexible cable. EP rubber-insulated CSP-sheathed having the
number of cores with cross-sectional areas as specified.
Apparatus and equipment, other than heating, requiring flexible cable connection
Circular flexible cable PVC-insulated PVC-sheathed having the number of cores with
cross-sectional areas specified.
The cores of all flexible cords shall be coloured throughout their length and colourcoded
to comply with the British Standard Specification.
PVC SWA cable
PVC-insulated single-cable armoured cables shall be 500/1000V grade and shall comply
with BS 6346:1969.
The cable shall comprise round or shaped conductors, of equal cross-sectional area,
composed of high-conductivity plain annealed copper cable insulated with PVC, coloured
for identification. The cores to be laid up circular and sheathed with PVC. The cable shall
be served with one layer of steel-cable armour and sheathed overall with PVC.
Design example 297
The cable shall be manufactured and supplied in one length on a suitable drum. No
through joints will be allowed. All cables shall be of one manufacture.
Where individual cables are run on the surface suitable supports shall be fitted to give
a minimum clearance of 15mm between cables and face of structure. Where cables are
installed vertically, the cable shall be gripped firmly by clamps of an approved pattern.
Where cables are grouped and run on the surface they shall be carried on wrought-iron
brackets or purpose-made clips of approved design, fixed at not more than 600mm
centres.
All PVC SWA cables run on the surface shall be adequately protected to a height of
2m from the ground.
Where PVC-insulated SWA cables are laid in the ground they shall be laid on not less
than 75mm of sand, covered by a further 75mm of sand and protected by means of
continuous interlocking warning tiles of approved pattern.
All cable trenches shall be excavated to a depth of 0.5m in unmade ground and 0.7m
where crossing roadways and backfilled by the builder who will also provide and install
all necessary cable ducts and earthenware pipes for cable entry into buildings, but the
electrical contractor shall be responsible for correctly marking out all cable routes,
supplying and installing waring tiles and marker posts, and generally supervising all work
in connection with the cable-laying requirements.
Cable joints
All cable runs between one definite terminal point and another throughout the whole of
the installation shall be installed without intermediate joints.
Luminaires
All luminaires shown and listed on the drawings and schedules shall be provided and
installed. Luminaires with non-standard suspension lengths shall be ordered to the correct
lengths to suit mounting height as indicated on the drawings and schedules. The
installation of luminaires shall include all necessary assembling, wiring and erection.
Terminations to non-pendant luminaires shall be in heat-resisting flexible cord with
porcelain-insulated terminal block connectors for connection to PVC-insulated cable or
PVC-insulated PVC-sheathed cable.
Fluorescent luminaires shall be mounted either directly or on suspensions from two
BS conduit boxes installed at the spacing required to suit the fitting.
Ceiling roses
Ceiling roses shall be white of reputable manufacture in accordance with BS 67. They
shall be of porcelain, or of plastic with porcelain interiors and shall be fitted with plastic
backplates or plastic mounting blocks semi-recessed where necessary to comply with the
IEE Regulations.
Where they are of the three-plate type the phase terminal shall be shrouded so as to
prevent accidental contact if the cover is removed.
Design of electrical services for buildings 298
Lamp holders
Lamp holders shall be of the bayonet-cap type for tungsten lamps up to and including
150W, and of the Edison screw type for larger lamps.
Where they are integral with lighting luminaires, they shall be brass with porcelain
interiors. For use with flexible pendants, they shall be of white plastic with compression
glands. Where batten lamp holders are installed the lamp holders shall be of white plastic.
In damp situations they shall be fitted with Home Office skirts.
Lamp holders for fluorescent tubes shall be of the heavy pattern bi-pin type of white
plastic construction.
All lampholders shall be lubricated with molybdenum disulphide to ensure easy
removal of threaded rings and lamps.
Lamps
Lamps shall be supplied and fitted to all points and luminaires shown and listed on the
drawings and schedules.
Tungsten filament lamps of 40–100W (inclusive) shall be of the coiled coil type.
Generally they shall be energy saving types. Lamps shall be pearl-finished when fitted in
open shades or in globes which are unobscured and shall be of the clear type when fitted
in closed units of opalescent glassware or any other type of luminaire elected where the
filament is not under direct vision.
The colour of all fluorescent lamps shall be the new white, 3500K.
Lighting circuits
Lighting circuits shall be installed on the loop-in system with three terminal-type ceiling
roses with shrouded live terminal, integral backplate, earth terminal and break-joint ring.
Looping shall not be carried out at switch positions.
No luminaire shall be connected directly to the hard wiring or have circuit wiring
passing through it.
Cables on one circuit are not to run through the BS boxes behind ceiling roses or
luminaires on other circuits.
Light switches
Flush switches shall be rocker-operated with white flush plastic plates of the singleswitch
or grid-switch type.
Surface switches shall be heavy-gauge steel with conduit entries and shall have
rocker-operated mechanisms. They shall have steel front plates of the single-switch or
grid-switch type.
Switches outdoors or otherwise exposed to damp conditions shall be of industrial
pattern watertight type with galvanized steel, or thermoplastic boxes and waterproof
gaskets.
Socket outlets
Design example 299
All socket outlets shall be of the switched type with rocker-operated switch mechanisms.
Flush socket outlets shall be of the insulated pattern with white or ivory finish.
Surface socket outlets shall be metal clad type with steel front plate.
Connections to space heaters
The circuit to each unit heater, fan convector and other similiar piece of heating
equipment shall terminate in a double-pole isolator from which the final connection shall
be made in heat-resisting rubber insulated cable in flexible conduit. The casing of the
heater shall be bonded to the earth continuity conductor.
Connections to motors and machinery
The circuit to each machine shall terminate in an isolator as near the machine as possible.
Where a motor starter is required it shall be placed adjacent to and immediately after the
isolator. The final connection from the isolator or starter to the machine shall be in PVCinsulated
cable in conduit. The rigid conduit shall terminate in a box approximately
300mm from the machine terminals and the final section from this point to the machine
shall be in flexible conduit. The metalwork of the machine shall be bonded to the earth
continuity conductor.
Regulations
The installation shall comply with Electricity at Work Regulations, Electricity Safety
Quality, and Continuity Regulations 2002 and any other applicable statutory regulations.
It shall conform with the Institution of Electrical Engineers’ Regulations for the Electrical
Equipment of Buildings BS 7671.
The installation and all material used shall comply with all relevant British Standards
and Codes of Practice.
Clearance from other services
All electric conduit and equipment shall be installed at least 150mm clear of any other
metalwork, and in particular of any water, gas, steam or chemical pipes.
Bonding and earthing
All conduit connections, boards, fittings, trunking, etc., shall be properly screwed
together so as to ensure proper mechanical and electrical continuity throughout.
Great care is to be taken in bonding and earthing the installation and tests are to be
carried out as the work progresses to check the electrical continuity of all metalwork,
conduits, etc., and earth continuity conductors. This is particularly important where work
is built into the fabric of the building.
For the purpose of estimating the electrical contractor may assume that he can earth to
the supply authority’s earthing terminal.
Design of electrical services for buildings 300
The electrical contractor shall contact the supply authority at an early stage in the
works to ensure that a suitable earthing terminal will be provided.
The electrical contractor shall be responsible for the bonding and earthing of all
exposed metalwork, structural or otherwise, and of the metalwork of any gas or water
service, to the earthing termination at the intake position, in accordance with IEE
Regulations BS 7671.
No earth continuity conductor shall be less than 1.5mm2 copper cable insulated and
coloured green and yellow.
The steel cable armouring of the sub-main cables shall be efficiently bonded together
and to the respective switchboard, distribution board, sealing chamber and conduits at
which they terminate and to all adjacent metalwork.
The frames of all electric motors and starting panels, etc., are to be efficiently earthed.
Where flexible metallic conduit is used, a stranded insulated and coloured green and
yellow copper cable of not less than 6mm2 is to be run from the terminal box through the
flexible metallic conduit to terminate in the first cast metal box in the conduit run.
The circuit protective conductor shall be attached at each end by means of a crimped
socket, brass screw and spring washer.
Pipelines, tanks, vessels and all other equipment associated with the piping or storage
of highly inflammable materials shall be statically bonded to an effective earth continuity
conductor by means of 30mm×10mm hard drawn tinned copper tape, secured by means
of the flange bolts. The earth continuity conductor shall be taken to an earth electrode and
bonded to it.
Earth electrode
Where an earth electrode is required it shall take the form of extensible copper earth rods
driven into the ground at suitable spacing. The number of rods and the depth to which
they are driven shall be determined according to the soil resistivity at the site to give an
earth resistance not exceeding 0.5ohms.
Concrete inspection covers shall be provided over every earth electrode and a means
shall be provided for disconnecting the bonding cable from every earth electrode.
Connection to and between electrodes shall be carried out in insulated stranded cable.
Testing
Continuity and insulation tests shall be carried out during installation.
At completion polarity, bonding, earth loop impedance, continuity and insulation tests
shall be carried out on the entire installation and in each part of it. The tests shall be
witnessed by the consulting engineer and shall be carried out in accordance with the
requirements of the Institution of Electrical Engineers’ Regulations BS 7671. A
completion certificate schedule of inspection, and schedule of test results as prescribed by
BS 7671 shall be provided.
Circuit lists and labels
Design example 301
At each distribution board a circuit schedule complying with BS 7671 IEE Wiring
Regulations shall be supplied and fixed on the inside of the distribution board door.
The schedule shall state clearly the position, number and wattage of lamps, socket
outlets, etc., which the fuseways/CBs control. A sample circuit schedule shall be
submitted for approval before installation.
On the cover of each distribution board, fuse switch, switch fuse, isolating switch and
starter a 45mm×20mm traffolyte label (white-black-white) shall be fixed and engraved in
5mm characters, giving details of the service position and phase, etc. In addition,
traffolyte (white-red-white) labels engraved in 8mm characters ‘400V’ shall be fixed to
all TPN distribution boards.
All labels shall be fixed by means of four 6mm round-headed brass screws.
Identification of cables
All power, instrument, control and indication cables shall be provided with indestructable
cable marking collars which shall bear the cable number. The marking collars shall be
fitted at every cable termination.
The individual cores of cables shall be numbered to indicate which terminal they are
connected to.
Fuses
HCR fuse links of the current rating shall be supplied and installed in all fuse carriers.
Design of electrical services for buildings 302
Cubicle panels
Main and distribution switchboards as listed in the schedules shall be purpose-made and
shall consist of a sheet-steel cubicle designed for access from front only or from front and
rear according to site position, containing distribution busbars, all cable terminations and
interconnections. All items. of switch and fusegear are to be flush-mounted on the front
of the cubicle which is to be finished grey stoved enamel.
Switchboards shall be suitable for controlling reduced voltage supplies and shall be
comprehensively tested before dispatch from the manufacturer’s works to ensure
satisfactory operation of all component parts. The tests shall include continuity and 2kV
flash tests. Busbar systems in switchboard shall be tested at 50kA for 1s.
Full protection shall be provided by means of mechanical interlocks with the covers
and operating levers, The switchboard shall have an earthing terminal and earthing bar.
External connections shall be provided to allow all outgoing cables to terminate at
either top or bottom of the switchboard.
Busbars
Busbar panels as shown on the drawings and listed in the schedules are to be of the
ratings indicated and are to be of high-conductivity copper mounted on robust vitreous
porcelain insulators complete with all necessary clamps. The busbars are to be enclosed
in a stove-enamelled sheet-steel casing with cast-iron frame members and detachable top,
bottom and side plates. The covers are to be of the screw-on type. The panels are to be
provided with all necessary holes and bushes for incoming and outgoing cables.
Incoming and outgoing switch fuses of the types and ratings shown on the drawings
and schedules shall be provided and installed adjacent to the busbar chamber. All
necessary interconnections between switch fuses and busbars shall be made and all the
equipment shall be fixed on a common angle-iron frame which is to be supplied as part of
the electrical contract. The frame is to be painted one coat primer and two coats grey
finish.
Where necessary, trunking shall be supplied and installed from busbars to meter
positions.
Fuse switches
Fuse switches shall be heavy-duty pattern fitted with HRC fuse links. They shall have
heavy-gauge steel enclosures with cast-iron frame members, rust-protected and finished
grey stoved enamel. Front access doors shall be fitted with dust-excluding gaskets and
shall be interlocked so that they cannot be opened when the switch is ‘on’. Operating
handles shall be lockable in both the on and off positions. The top and bottom endplates
shall be removable.
Each fuse switch shall be supplied complete with the correct HRC fuse links.
Each fuse switch shall have flag on-off indication.
Design example 291
Fuse switches shall be 500V rating and shall be clearly marked with their current
rating, and the items of equipment that they serve.
Switch fuses
Switch fuses shall be industrial pattern dust-proof type with HRC fuse links. They shall
have enclosures fabricated from sheet steel finished grey stoved enamel with removable
top and bottom endplates and shall have doors fitted with dust-proof gaskets. They shall
have front-operated handles with visible on-off indication.
The interiors shall have vitreous porcelain bases fitted with plated non-ferrous
conducting components. Switches shall be of the quick make-and-break type and have
removable shields over the fixed contacts and removable moving contact bars.
Each switch fuse shall be supplied complete with the correct HRC fuse links.
Switch fuses shall be 500V rating and shall be clearly marked with their current rating,
and the items of equipment that they serve.
Isolators
Isolators shall be heavy-duty pattern with steel enclosures having cast-iron frame
members, rust-protected and finished grey stoved enamel. Front access doors shall be
fitted with dust-excluding gaskets and shall be interlocked so that they cannot be opened
when the switch is ‘on’. Operating handles shall be lockable in both the on and off
positions and shall have visible on-off indication.
Isolators shall be 500V rating and shall be clearly marked with their current rating.
The moving contact assemblies are to be removable for inspection and maintenance.
Distribution boards
All distribution boards shall be single-pole or triple-pole with neutral bar, and with
fuseways/CBs 20 or 30A or above as specified.
All distribution boards shall be of the surface pattern in heavy sheet-steel cases of the
500V range with HRC fuse carriers.
On all triple-pole and neutral distribution boards the number of neutral terminals to be
provided shall be the same as the total number of fuse-ways/CBs in the board. This
information must be given to the manufacturers when ordering, together with information
with regard to composite boards having a multiplicity of fuse ratings as specified.
In the case of flush installations, the distribution boards shall be mounted over flush
adaptable iron boxes into which the conduits and wiring of the system will terminate. The
boxes shall be of a size to be agreed on site with the consulting engineer.
Doors of all distribution boards shall be lockable either by means of a barrel-type lock
with detachable key or by means of a modified door-fixing screw, bracket and padlock.
Ample clearance shall be provided between ‘live’ parts and the sheet-steel protection
to allow cables to be brought to their respective terminals in a neat and workmanlike
manner.
To separate opposite poles a fillet of hard incombustible insulating material shall be
provided of sufficient depth to reach the inside of the door.
Design of electrical services for buildings 292
In each distribution board spare fuse carriers shall be provided and held in place by a
suitable clip so that the carrier cannot be inadvertently dislodged.
Distribution boards shall be fixed at a height to give easy access, and be provided with
a schedule complying with 514–09–01 of BS 7671.
Starters
A starter shall be provided for each motor as indicated on the drawings and schedules.
The starters shall be surface-mounted with a sheet-steel case containing a triple-pole
contactor with vertical double break per pole having silver-faced contacts. They are to
have continuously rated operating coils with inherent undervoltage release. Operating
coils are to be supplied from phase to neutral. The starters shall have magnetic-type
overload relays with adjustable oil dashpot time lags and stop/reset push-buttons in the
front cover. The cover is also to contain the start push-button.
Starters are to have single-pole auxiliary switches and shall incorporate single-phase
protection.
Star-delta starters shall have a time-delay device complete with all main and control
wiring and terminal block for incoming and outgoing cables. The time-delay device shall
be of the pneumatic pattern with an instantaneous reset allowing restarting immediately
after a star-delta switching operation. The star and delta contactors are to be mechanically
and electrically interlocked.
The overload relays are to be correctly set to ensure adequate protection without
nuisance tripping.
Steel conduit
All steel Class ‘B’ conduits and conduit fittings throughout the whole of this installation
shall comply in all respects with British Standard Specification BS 31:1940. All PVC
insulated cables, other than flexibles, shall be protected throughout their length with
heavy-gauge screwed welded conduit (enamelled or galvanized as required) with the
necessary malleable iron loop-in, draw-in, angle and outlet boxes. No type of ‘elbow’ or
‘tee’ will be allowed on works under this Specification.
Where adaptable boxes are used they shall be of cast iron or heavy-gauge sheet steel
of not less than 12-gauge.
No conduit of less than 20mm diameter shall be used.
A solid coupling shall be inserted in every flush conduit run at the point where it
leaves a ceiling, wall or floor for ease of dismantling if required.
Except where otherwise stated conduit is to be finished black enamel.
No conduit shall be installed with more than two right-angle bends without draw-in
boxes and draw-in boxes shall not be more than 8m apart.
All conduits, except where otherwise specified, shall drop not rise to the respective
points. In no circumstances shall the conduit be erected in such a manner as to form a U
without outlet, or in any other way that would provide a trap for condensed moisture.
Provision shall be made for draining all conduits or fixtures by a method approved by
the consulting engineer.
Design example 293
No ceiling looping-in point box shall be used as a draw-in box for any other circuit
than that for which such point box is intended.
Ceiling point boxes are to be of medium pattern malleable iron, with fixing holes at
50mm centres and conforming to BS Specification.
Flush ceiling point boxes which do not finish flush with the finished surface of the
ceiling, etc., shall be fitted with malleable iron extension rings.
Horizontal or diagonal runs of flush conduit on structural or partition walls will not be
permitted. All flush conduits shall drop or rise vertically to their respective points.
Connections between conduits and trunking and conduit and steel boxes, or between
conduit and steel cases of distribution gear or equipment, shall be made by means of a
flanged coupling and brass smooth-bore entry bush. The lead washer shall be fitted on the
inside of the trunking or box, etc.
All lids for draw-in boxes, etc., whether of the BS or adaptable type, shall be of heavy
cast-iron or 12-gauge sheet steel, and shall be fixed (overlapping for flush work) by
means of two or four M6 round-headed brass screws as required.
Conduits set through walls will not be permitted. When change of direction is required
after passing through a wall an appropriate back outlet box is to be fitted.
All joints between lengths of conduit, or between conduit and fittings, etc., are to be
threaded home and butted.
Sets and bends are to be made without indentation, and the bore must be full and free
throughout. All screw-cutting oil must be carefully wiped off before joining up.
Conduit runs, as far as possible, are to be symmetrical and equally spaced.
The electrical contractor must take all precautions in situations likely to be damp to
see that all conduits and boxes in the vicinity are rendered watertight.
During the progress of the work all exposed ends of conduits shall be fitted with
suitable plastic or metal plugs. Plugs of wood, paper and the like will not be acceptable as
sufficient protection.
Lighting, heating, power and any other types of circuit shall be run in separate
conduits and no circuit of any one system shall be installed in any conduit or box of any
other system.
The proposed runs shall be submitted to the consulting engineer for approval before
work is commenced.
Conduit fittings
All conduit fittings shall be of malleable iron which shall conform to the British
Standards Specification BS 31:1940.
All fittings shall be of the screwed pattern, and no solid or inspection elbows, tees or
bends shall be installed. Generally, all conduit fittings shall be stove-enamelled black or
other approved finish inside and out, but where galvanized conduit is installed, all fittings
shall be galvanized by the hot process both inside and out. Such fittings shall be of Class
B pattern.
All conduit fittings not carrying lighting or other fittings shall be supplied with
suitable cast-iron covers with round-head brass screws. Where flush boxes are installed
the covers shall be of the overlapping rustproof pattern.
Design of electrical services for buildings 294
All ceiling point boxes, except in the case of surface conduits, shall finish flush with
the underside of the ceiling, extension rings being used where necessary.
Every flush ceiling point box to which a luminaire is to be attached shall be fitted with
a break-joint ring of approved type.
Where surface conduit is used in conjunction with distance saddles, special boxes shall
be used, to obviate the setting of conduit when it enters or leaves the boxes.
All conduit boxes, including boxes on and in which fittings, switches and socket
outlets are mounted, shall be securely fixed to the walls and ceilings by means of not less
than two countersunk screws, correctly spaced, and the fixing holes shall be countersunk,
so that the screw heads do not project into the box.
Flexible conduit
Connections to individual motors and heating equipment run in conduit shall be made
using a minimum of 300mm of watertight flexible conduit. The conduit shall be Kopex
LS/2.
Flexible conduit connecting to heating equipment shall employ butyl rubber insulated
CSP sheathed cables and suitable terminal blocks shall be used in all boxes where a
change in cable type is involved.
Earth continuity of all flexible conduits shall be maintained by 4mm2 minimum copper
conductors forming one of the cores of the cable.
Flexible conduits shall be terminated with the Kopex couplings and connectors
specially made for the purpose.
Cable trunking
Cable trunking shall be supplied and installed complete with fittings and accessories and
shall be of an approved manufacture. It shall be manufactured from zinc or lead-coated
sheet steel finished stove enamelled grey or galvanized and shall be of 18swg for sizes up
to and including 75mm×75mm section and 16swg for sizes above.
All bends, tees, reducers, couplings, etc., shall be of standard pattern: where it is
necessary for a special fitment to be used, it is to be fabricated by the manufacturers.
Where it is necessary to provide additional trunking over fixings, these shall be
supplied by the manufacturer and shall be applied with the manufacturer’s special tools.
Where holes or apertures are formed in the trunking for cable entry, they shall be
bushed with brass smooth-bore entry bushes, or PVC grommet strips. Cable supports are
to be inserted in vertical runs of trunking and cables are to be laced thereto in their
respective groups.
Fire barriers of hard insulating material shall be provided in vertical runs of trunking
where they pass through floors.
Where more than one service is involved multi-compartment trunking shall be
employed to separate the services.
Cable tray
Design example 295
Cable tray is to be made of 16-gauge perforated mild-steel sheet and is to be complete
with all coupling pieces and bends, offsets and fixing brackets, to enable the tray to fit the
structure accurately.
Where cables are taken over the edge of the tray they shall be protected by rubber
grommets.
MICC cable
Mineral-insulated metal-sheathed cables shall be high-conducting copper conductors
embedded in magnesium oxide and sheathed with copper with an overall covering of
PVC.
All cable terminations shall be protected and sealed with ring-type glands with screwon
pot-type seals utilizing cold plastic compound and neoprene sleeving all of an
approved pattern, and applied with the special tools recommended by the cable
manufacturers.
Cold screw-on pot-type seals shall be used except where the ambient temperature in
which the cable will operate will exceed 170°F, where the hot-type seal shall be used.
Four-core MICC cables shall not be used for ring circuits.
Vibration-absorbing loops shall be formed in MICC cables connected to motors and
other vibrating equipment.
Connections and joints in MICC cables shall only be made at the terminals of
switches, ceiling roses, or at connector blocks housed in outlet boxes. Connector blocks
shall have a minimum of two screws per conductor.
Where entry is made into equipment which does not have a spouted entry, the cable
shall be made off by means of coupling, male bush, and compression washer.
MICC cables shall be neatly installed and shall be clipped by means of copper saddles
secured by two brass screws. Where two, three or four cables are run together multiple
saddles shall be used.
MICC cables shall be delivered to the site with the manufacturers’ seals and
identification labels intact and shall be installed in accordance with the manufacturers’
recommendations and using the specialized tools recommended by the manufacturer.
They shall be tested when installed before being sealed and again at the end of the
contract.
They shall be sealed against the ingress of moisture at all times during the contract.
PVC cable
Cable PVC-insulated only, and PVC-insulated PVC-sheathed cable shall be 600/1000V
grade to BS 6004:1969.
The cable shall be delivered to site on reels, with seals and labels intact and shall be of
one manufacturer throughout the installation.
The cable shall be installed direct from the reels and any cable which has become
kinked, twisted or damaged in any way shall be rejected. The installation shall be cabled
on the loop-in system, i.e. wiring shall terminate at definite points (switch positions,
lighting points, etc.) and no intermediate connections or joints will be permitted. Cables
shall not pass through or terminate in lighting fittings.
Design of electrical services for buildings 296
Where it is necessary to make direct connection between the hard wiring and flexible
cord, this shall be done by means of porcelain-shielded connectors with twin screws. No
luminaire shall be connected directly to the hard wiring.
The terminations shall be suitable for the type of terminal provided and shall be either
sweated lugs of appropriate size, or eyelet or crimped type cable terminations, all of
reputable manufacture. Shakeproof washers shall be used where electric motors are
connected.
Where cable cores are larger than terminal holes, the cables shall be fitted with
thimbles. For all single connections, they shall be doubled or twisted back on themselves
and pinching screws shall not be permitted to cut the conductors. Cables shall be firmly
twisted together before the connection is made.
In no circumstances shall cables be trapped under plain washers as a termination.
Cables shall be coloured in accordance with IEE Regulations BS 7671.
Only two cables shall generally be bunched together at one terminal. In exceptional
cases three cables may be bunched together at one terminal with the authority of the
engineer given on site.
Flexible cords
All flexible cords shall comply with British Standard Specification BS 6500:1969, and
shall consist of high-conductivity tinned copper conductors of the required crosssectional
area insulated and sheathed as detailed hereunder:
Lighting pendants
Two-core 0.75mm2 heat-resisting circular flexible cord EP rubber-insulated CSPsheathed.
Colour of sheath, white.
Heating apparatus and equipment requiring flexible cable connection
Heat-resisting circular flexible cable. EP rubber-insulated CSP-sheathed having the
number of cores with cross-sectional areas as specified.
Apparatus and equipment, other than heating, requiring flexible cable connection
Circular flexible cable PVC-insulated PVC-sheathed having the number of cores with
cross-sectional areas specified.
The cores of all flexible cords shall be coloured throughout their length and colourcoded
to comply with the British Standard Specification.
PVC SWA cable
PVC-insulated single-cable armoured cables shall be 500/1000V grade and shall comply
with BS 6346:1969.
The cable shall comprise round or shaped conductors, of equal cross-sectional area,
composed of high-conductivity plain annealed copper cable insulated with PVC, coloured
for identification. The cores to be laid up circular and sheathed with PVC. The cable shall
be served with one layer of steel-cable armour and sheathed overall with PVC.
Design example 297
The cable shall be manufactured and supplied in one length on a suitable drum. No
through joints will be allowed. All cables shall be of one manufacture.
Where individual cables are run on the surface suitable supports shall be fitted to give
a minimum clearance of 15mm between cables and face of structure. Where cables are
installed vertically, the cable shall be gripped firmly by clamps of an approved pattern.
Where cables are grouped and run on the surface they shall be carried on wrought-iron
brackets or purpose-made clips of approved design, fixed at not more than 600mm
centres.
All PVC SWA cables run on the surface shall be adequately protected to a height of
2m from the ground.
Where PVC-insulated SWA cables are laid in the ground they shall be laid on not less
than 75mm of sand, covered by a further 75mm of sand and protected by means of
continuous interlocking warning tiles of approved pattern.
All cable trenches shall be excavated to a depth of 0.5m in unmade ground and 0.7m
where crossing roadways and backfilled by the builder who will also provide and install
all necessary cable ducts and earthenware pipes for cable entry into buildings, but the
electrical contractor shall be responsible for correctly marking out all cable routes,
supplying and installing waring tiles and marker posts, and generally supervising all work
in connection with the cable-laying requirements.
Cable joints
All cable runs between one definite terminal point and another throughout the whole of
the installation shall be installed without intermediate joints.
Luminaires
All luminaires shown and listed on the drawings and schedules shall be provided and
installed. Luminaires with non-standard suspension lengths shall be ordered to the correct
lengths to suit mounting height as indicated on the drawings and schedules. The
installation of luminaires shall include all necessary assembling, wiring and erection.
Terminations to non-pendant luminaires shall be in heat-resisting flexible cord with
porcelain-insulated terminal block connectors for connection to PVC-insulated cable or
PVC-insulated PVC-sheathed cable.
Fluorescent luminaires shall be mounted either directly or on suspensions from two
BS conduit boxes installed at the spacing required to suit the fitting.
Ceiling roses
Ceiling roses shall be white of reputable manufacture in accordance with BS 67. They
shall be of porcelain, or of plastic with porcelain interiors and shall be fitted with plastic
backplates or plastic mounting blocks semi-recessed where necessary to comply with the
IEE Regulations.
Where they are of the three-plate type the phase terminal shall be shrouded so as to
prevent accidental contact if the cover is removed.
Design of electrical services for buildings 298
Lamp holders
Lamp holders shall be of the bayonet-cap type for tungsten lamps up to and including
150W, and of the Edison screw type for larger lamps.
Where they are integral with lighting luminaires, they shall be brass with porcelain
interiors. For use with flexible pendants, they shall be of white plastic with compression
glands. Where batten lamp holders are installed the lamp holders shall be of white plastic.
In damp situations they shall be fitted with Home Office skirts.
Lamp holders for fluorescent tubes shall be of the heavy pattern bi-pin type of white
plastic construction.
All lampholders shall be lubricated with molybdenum disulphide to ensure easy
removal of threaded rings and lamps.
Lamps
Lamps shall be supplied and fitted to all points and luminaires shown and listed on the
drawings and schedules.
Tungsten filament lamps of 40–100W (inclusive) shall be of the coiled coil type.
Generally they shall be energy saving types. Lamps shall be pearl-finished when fitted in
open shades or in globes which are unobscured and shall be of the clear type when fitted
in closed units of opalescent glassware or any other type of luminaire elected where the
filament is not under direct vision.
The colour of all fluorescent lamps shall be the new white, 3500K.
Lighting circuits
Lighting circuits shall be installed on the loop-in system with three terminal-type ceiling
roses with shrouded live terminal, integral backplate, earth terminal and break-joint ring.
Looping shall not be carried out at switch positions.
No luminaire shall be connected directly to the hard wiring or have circuit wiring
passing through it.
Cables on one circuit are not to run through the BS boxes behind ceiling roses or
luminaires on other circuits.
Light switches
Flush switches shall be rocker-operated with white flush plastic plates of the singleswitch
or grid-switch type.
Surface switches shall be heavy-gauge steel with conduit entries and shall have
rocker-operated mechanisms. They shall have steel front plates of the single-switch or
grid-switch type.
Switches outdoors or otherwise exposed to damp conditions shall be of industrial
pattern watertight type with galvanized steel, or thermoplastic boxes and waterproof
gaskets.
Socket outlets
Design example 299
All socket outlets shall be of the switched type with rocker-operated switch mechanisms.
Flush socket outlets shall be of the insulated pattern with white or ivory finish.
Surface socket outlets shall be metal clad type with steel front plate.
Connections to space heaters
The circuit to each unit heater, fan convector and other similiar piece of heating
equipment shall terminate in a double-pole isolator from which the final connection shall
be made in heat-resisting rubber insulated cable in flexible conduit. The casing of the
heater shall be bonded to the earth continuity conductor.
Connections to motors and machinery
The circuit to each machine shall terminate in an isolator as near the machine as possible.
Where a motor starter is required it shall be placed adjacent to and immediately after the
isolator. The final connection from the isolator or starter to the machine shall be in PVCinsulated
cable in conduit. The rigid conduit shall terminate in a box approximately
300mm from the machine terminals and the final section from this point to the machine
shall be in flexible conduit. The metalwork of the machine shall be bonded to the earth
continuity conductor.
Regulations
The installation shall comply with Electricity at Work Regulations, Electricity Safety
Quality, and Continuity Regulations 2002 and any other applicable statutory regulations.
It shall conform with the Institution of Electrical Engineers’ Regulations for the Electrical
Equipment of Buildings BS 7671.
The installation and all material used shall comply with all relevant British Standards
and Codes of Practice.
Clearance from other services
All electric conduit and equipment shall be installed at least 150mm clear of any other
metalwork, and in particular of any water, gas, steam or chemical pipes.
Bonding and earthing
All conduit connections, boards, fittings, trunking, etc., shall be properly screwed
together so as to ensure proper mechanical and electrical continuity throughout.
Great care is to be taken in bonding and earthing the installation and tests are to be
carried out as the work progresses to check the electrical continuity of all metalwork,
conduits, etc., and earth continuity conductors. This is particularly important where work
is built into the fabric of the building.
For the purpose of estimating the electrical contractor may assume that he can earth to
the supply authority’s earthing terminal.
Design of electrical services for buildings 300
The electrical contractor shall contact the supply authority at an early stage in the
works to ensure that a suitable earthing terminal will be provided.
The electrical contractor shall be responsible for the bonding and earthing of all
exposed metalwork, structural or otherwise, and of the metalwork of any gas or water
service, to the earthing termination at the intake position, in accordance with IEE
Regulations BS 7671.
No earth continuity conductor shall be less than 1.5mm2 copper cable insulated and
coloured green and yellow.
The steel cable armouring of the sub-main cables shall be efficiently bonded together
and to the respective switchboard, distribution board, sealing chamber and conduits at
which they terminate and to all adjacent metalwork.
The frames of all electric motors and starting panels, etc., are to be efficiently earthed.
Where flexible metallic conduit is used, a stranded insulated and coloured green and
yellow copper cable of not less than 6mm2 is to be run from the terminal box through the
flexible metallic conduit to terminate in the first cast metal box in the conduit run.
The circuit protective conductor shall be attached at each end by means of a crimped
socket, brass screw and spring washer.
Pipelines, tanks, vessels and all other equipment associated with the piping or storage
of highly inflammable materials shall be statically bonded to an effective earth continuity
conductor by means of 30mm×10mm hard drawn tinned copper tape, secured by means
of the flange bolts. The earth continuity conductor shall be taken to an earth electrode and
bonded to it.
Earth electrode
Where an earth electrode is required it shall take the form of extensible copper earth rods
driven into the ground at suitable spacing. The number of rods and the depth to which
they are driven shall be determined according to the soil resistivity at the site to give an
earth resistance not exceeding 0.5ohms.
Concrete inspection covers shall be provided over every earth electrode and a means
shall be provided for disconnecting the bonding cable from every earth electrode.
Connection to and between electrodes shall be carried out in insulated stranded cable.
Testing
Continuity and insulation tests shall be carried out during installation.
At completion polarity, bonding, earth loop impedance, continuity and insulation tests
shall be carried out on the entire installation and in each part of it. The tests shall be
witnessed by the consulting engineer and shall be carried out in accordance with the
requirements of the Institution of Electrical Engineers’ Regulations BS 7671. A
completion certificate schedule of inspection, and schedule of test results as prescribed by
BS 7671 shall be provided.
Circuit lists and labels
Design example 301
At each distribution board a circuit schedule complying with BS 7671 IEE Wiring
Regulations shall be supplied and fixed on the inside of the distribution board door.
The schedule shall state clearly the position, number and wattage of lamps, socket
outlets, etc., which the fuseways/CBs control. A sample circuit schedule shall be
submitted for approval before installation.
On the cover of each distribution board, fuse switch, switch fuse, isolating switch and
starter a 45mm×20mm traffolyte label (white-black-white) shall be fixed and engraved in
5mm characters, giving details of the service position and phase, etc. In addition,
traffolyte (white-red-white) labels engraved in 8mm characters ‘400V’ shall be fixed to
all TPN distribution boards.
All labels shall be fixed by means of four 6mm round-headed brass screws.
Identification of cables
All power, instrument, control and indication cables shall be provided with indestructable
cable marking collars which shall bear the cable number. The marking collars shall be
fitted at every cable termination.
The individual cores of cables shall be numbered to indicate which terminal they are
connected to.
Fuses
HCR fuse links of the current rating shall be supplied and installed in all fuse carriers.
Design of electrical services for buildings 302
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