C العدادات

C. DISTRIBUTION BOARDS


C.1. STANDARDS:

Distribution board shall comply with the following standards as appropriate:-

IEC/BS EN 61439-1

Low-voltage switchgear and controlgear assemblies –
Part 1: General rules
IEC/BS EN 61439-2 Part 2: Power switchgear and controlgear assemblies
IEC/BS EN 61439-3

Part 3: Distribution boards intended to be operated by
ordinary persons (DBO)
IEC/BS EN 61439-4 Part 4: Particular requirements for assemblies for
construction sites (ACS)
IEC/BS EN 61439-5

Part 5: Assemblies for power distribution in public
networks
IEC/BS EN 60947-1

Low-voltage switchgear and controlgear –
Part 1: General rules
IEC/BS EN 60947-2 Part 2: Circuit-breakers
IEC/BS EN 60947-3 Part 3: Switches, disconnectors, switch-disconnectors and
fuse-combination units
IEC/BS EN 60947-4-1

Part 4-1: Contactors and motor-starters -
Electromechanical contactors and motor-starters
IEC/BS EN 60947-5-1

Part 5-1: Control circuit devices and switching elements -
Electromechanical control circuit devices
IEC/BS EN 60947-6-1

Part 6-1: Multiple function equipment - Transfer switching
equipment
IEC/BS EN 60898-1

Electrical accessories - Circuit breakers for overcurrent
protection for household and similar installations Circuit-
breakers for a.c. operation

IEC/BS EN 61008-1

Residual current operated circuit-breakers without integral
overcurrent protection for household and similar uses
(RCCB's): General rules
IEC/BS EN 60529


Degrees of protection provided by enclosures
IEC/BS EN 60269-1


Low-voltage fuses - General requirements
IEC/BS EN 61869-1,2

Instrument/Current Transformers
BS 159


High-Voltage Busbars and Busbar Connections




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C.2 ENCLOSURE:

C.2.1 Distribution Board shall be flush or surface mounting. Enclosure shall be fabricated from Zinc
coated or pre hot dip galvanized sheet steel of minimum thickness of l.5mm.

C.2.2 The Distribution Board shall be provided with fixed cover and a hinged door with padlocking
which can be opened without any obstruction about 120 o and conduit knock outs from the top
and bottom. The hinged door can be an integral part of the fixed cover.

C.2.3 The steel Enclosure shall be protected to IP31 for internal use with neoprene gasket for the
doors and IP54 for outdoor and damp locations.


C.3 GENERAL:

C.3.1 The arrangement of the enclosure shall be such that the switch, MCB and RCCB cannot be
operated without opening the hinged doors. To obtain access to MCB & RCCB it should be
necessary to remove the fixed cover.

C.3.2 Miniature circuit breakers (M.C.B) or H.R.C. fuses can be used as detailed in the Drawings for
Distribution Board used as sub -main Switchboards. For final Distribution Board Miniature
Circuit Breakers shall be used, unless otherwise specified.

C.3.3 Final Distribution Boards serving lightin g and power shall be of split type, adequately rated
copper busbar pattern with 30mA current operated earth leakage circuit breaker (RCCB) serving
one Busbar and maximum 300mA RCCB serving the lighting busbar.

C.3.4 The final Distribution Boards shall be controlled by an adequately rated ON load switch to
interrupt the supply to the entire Distribution Board.

C.3.5 The number of ways of any Final Distribution Board shall not exceed 12 way for TP&N D.B's
and 16 ways for SP &N D.B's including spare. Separate Distribution Boards for lighting and
power can be used in case of intent to exceed the limited above.

C.3.6 The arrangement of the M.C.B. in the triple pole Distribution Board shall allow replacing a
triple pole M.C.B. with three adjacent single pole M.C.B's and vice versa.

C.3.7 The Distribution Board shall be equipped with neutral and earth bars, each having separate
terminal for each way of the Distribution Board and one for each of the main neutral and earth.
The Distribution Board shall be provided with cable gland where required.

C.3.8 A circuit label shall be provided to indicate the area served by each M.C.B.

C.3.9 The Contractor shall submit before ordering the Distribution board full technical details of the
components complete with supporting Manufacturer's catalogues , in addition to a dimensional
drawing showing the internal arrangement of the component.


C.4 RESIDUAL CURRENT CIRCUIT BREAKER (RCCB):

C.4.1 Current operated earth leakage circuit breaker shall provide accident protection by
interrupting dangerous contact with voltages which may be present in faulty electrical
appliances as a result of frame faults, insufficient insulation or misuse.



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C.4.2 The RCCB shall also provide a high degree of protection against earth leakage, fires and electric
shock and shall withstand at least 3 K.A. of short circuit making and breaking current. The
breakers shall fully comply with the requirements of IEC/BS EN 61008-1.

C.4.3 The breaker shall consist of a core balance transformer, a tripping coil with contact assembly,
main supply contacts, ON/OFF switch, a test button and a trip free mechanism, all enclosed in a
robust body of all insulated materials.

C.4.4 Degree of protection against earth leakage throughout the electrical installation shall be of the
following:

Maximum l0mA trip rating - for under water lighting

Maximum 30mA trip rating - all socket outlets and domestic apparatus

Preferably 300mA and - Lighting circuits and all other apparatus and
Maximum 500mA trip rating equipment such as A/C plants, lifts, pumps, etc...


C.5 MINIATURE CIRCUIT BREAKER (MCB):

C.5.1 The M.C.B. shall comply with IEC/BS EN 60898 and shall have a tripping characteristics of
Type B, except for motor circuit application where Type C shall be provided. The rated short
circuit breaking capacity of MCB shall be at least 3000A and the energy limiting class shall be of
class 3 in accordance with table ZA1 and ZA2 of IEC/BS EN 60898.

C.5.2 The frame size of all M.C.B.‟s shall be the same for possible interchangeability.

C.5.3 The M.C.B. shall either be of the plug in or bolt-on type.

C.5.4 Circuit breakers dollies shall be of the trip free pattern to prevent closing the breaker on a faulty
circuit, and shall be engraved to indicate "ON/OFF" position and rated current.

C.5.5 Miniature circuit breakers of built in earth leakage protection shall be used when required.
















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