MCB DISTRIBUTION BOARDS 6.1 Description

6.1.1 The specification hereunder shall be applied to al panel boards referenced on the drawings/load schedules as DB's.

The distribution board shall be flush / surface mounted split busbar type and shall be provided with standard extension box to allow cable glanding if required. The distribution board shall be surface mounted when installed within the electrical room/service rooms.

Distribution boards shall be provided with an isolator incomer with common ELCB’s for group of lighting circuits and common ELCB’s for group of power circuits for each section of MCB’s or RCBO’s for each power circuit as shown on schedules.

6.1.3 As a standard item, all MCB boards shall be provided with permanent circuit identification charts to the approval of the engineer.

6.1.4 MCB’s shall comply with IEC – 898 and RCBO’s shall comply with BSEN 61009. ELCB’s shall comply with BSEN 61008.

6.2 Enclosures

6.2.1 The MCB Distribution Boards shall be surface/flush mounted type. The enclosures within Electrical rooms shall be surface mounting type. The enclosures shall be powder coated rustproof sheet steel units, complete with circuit breakers providing thermal overload and magnetic short-circuit and earth fault protection as shown on the drawings. The enclosure protection shall be IP 31, while the complete assembly shall comply with IEC – 439-1.

6.3 Busbar

6.3.1 The MCBs shall be mounted on either 3 phase or single phase or split busbars as appropriate. All spaces which are not provided with breakers shall be covered with blank plates.

6.3.2 A final sub-circuit neutral assembly and an earthing bar assembly shall be available to facilitate the connection of neutral conductors and protective conductors respectively.

6.4 Breakers

6.4.1 Miniature circuit breakers, RCBO’s and earth leakage circuit breaker and shall be provided as indicated on the load schedules.

6.4.2 The short circuit rating for the MCB’s and RCBO’s shall be 10KA.

6.4.3 All circuit breakers shall be factory calibrated to ambient temperature of 50 deg.C.

7.0 Air Circuit Breakers

7.1 Air Circuit Breakers shall be designed and constructed to have a short circuit breaking capacity of not less than 50 kA and shall comply with the latest editions of IEC 947-2 and

BS 4752. They shall be of the fully withdrawable type and motor operated. ACB On/Off pushbuttons with On/Off indication lamps shall be provided.

ACBs shall be 3 or 4 pole type as indicated on drawings.

7.2 Suitable automatic safety shutters shall be provided to cover live parts when the ACB is in the withdrawn position. There shall be 3 distinct positions i.e.

"Connected"

"Test"

"Disconnected-Isolated"

There shall also be a "Withdrawn" position.

7.3 ACB's shall have adequately designed Arc chutes and Arc shields for fast and effective Arc chopping. The protective release shall be of the solid state electronic type having protection against overloads, short circuits and ground fault with adjustable time and current settings. The following protections shall be included :

(a) Overload protection (LT)

8.1 Moulded case circuit breakers shall conform to the latest editions of BS 4752 and IEC 947-2. The short circuit breaking capacities of the MCCB's installed in the main LV switchboards shall be at least 50 kA and 35KA in SMDB’s. The MCCBs used on the project shall be of the plug-in type.

8.2 MCCB's shall be of the heavy-duty quick make break type. All MCCB's shall be ambient temperature compensated to give the ratings indicated in the drawings at 50°C for which a formal certificate confirming that MCCB's have been temperature compensated should be furnished. Each breaker shall have on each phase a thermal over current release and also an instantaneous magnetic trip both of the adjustable type. Four pole breakers shall have a common trip both with a single operating handle and designed so that any overload in one pole automatically causes all poles to open.

Breakers shall be trip free and each shall have a trip indication independent of ON or OFF positions. To reset from the tripped position the mechanism shall first pass through the off position. Tripped indication shall be clearly shown by the breaker handle taking a position between ON and OFF.

8.3 The MCCB’s in LV MDB’s and MCC’s as shown on drawings shall be withdrawable type.

9.0 Disconnect Switches

9.1 Disconnect switches and isolator shall comply with IEC-947.

9.2 Disconnect switches shall be provided at each motor controller and appliance location . Isolators shall be rated to connect and disconnect 5 to 7 times the rated current of the item being switched. Isolators shall have a fully visual braking characteristic. Isolator enclosures shall be made of aluminium alloy to IP-65 and shall be provided with padlockable handle interlocked with the door. Isolators exposed to weather shall be housed within self-extinguished polyester loaded fiberglass panels to IP65.

10.0 Earth Leakage Circuit Breakers(ELCB's)

10.1 Current operated Earth leakage Circuit breakers shall comply with BS EN 61008.

10.2 The ELCB's shall have a residual current operated electromechanical release and shall incorporate a filtering device to eliminate unwanted tripping due to transient voltage. A test button is to prove operation of the ELCB.

The ELCB's shall have 100mA sensitivity for lighting circuits and 30mA for power circuits.

11.0 Contactors / Overload Relays/ Control Relays/Timers 11.1 Contactors:

Contactors shall be in conformance to IEC 947-4 / CSA 22.2 No.14 and shall be CE approved / CSA Certified.

The magnets and contact movements of the contactor shall be horizontal. The contacts shall be double break, butt type and each moving contact shall be individually spring loaded. The fixed and moving contacts shall be of silver -cadmium oxide. The contactor coils shall be continuously rated and shall be wound on moulded formers. Contactors shall be factory calibrated, ambient temperature compensated and sealed. It shall be possible to attach the contactors to 35mm DIN Mounting Rail (EN 50 022). Power contactors shall be provided with a minimum of 2 NO and 2 NC Auxiliary contacts.

The contactors shall provide greater performance in less panel space. There shall be flexibility in the selection of front mounting or side mounting of auxiliary contacts .The contactor shall design features for IP 2LX finger protection against accidental contact with live components, positive drive contacts and protection against manual operation, Auxiliary and relay contacts shall be compatible with electronic circuits to 17V, 5mA.

11.2 Overload Relays

Overload relays shall confirm to IEC 947-4 /CSA C22.2 No 14 and shall be CSA certified / CE approved.

The motor overload protection should have a protection choice of trip class 10 or 20. As a standard, the overload relay shall offer a manually operated trip function, visible trip indicator and isolated N.O. alarm contacts are to be used to protect motor circuits against overloads, phase sequence, phase failure (single phasing) and under voltage conditions. The relay range selected shall be such that the full load current of the equipment falls well within the relay adjustment range. The energy consumption of the relay shall be not above 150mW.

11.3 Control Relays

Control relays shall conform to IEC 255-10-00 and shall be CSA certified.

Control relays shall be of plug in type and shall have built in LED’s. They shall have miniature square bases with blade terminals. The contacts shall be of silver cadmium rated for 5A continuos current. The control relays shall be suitable for wiring with spade type crimped lugs.

11.4 Timers

Timers shall conform to IEC 255-1 and shall be CSA certified.

Timer relays with adjustable range for the Star delta starter shall ensure precise reproducibility of the timing function. The relay shall be equipped with Single pole double throw 1 Pole change over contact two electrically separated time delayed contact one normally open and one normally close.

12.0 Indication lamps / Push Buttons / Selector switches.

12.1 Indicating lamps:

The Indicating lamps shall be LED type.

12.2 Push Buttons:

Push button shall be flush type with colors in accordance with BS4099. Push Buttons contact blocks shall have double break silver plated contacts in NO / NC configuration rated not less than 5A resistive at 240AC, 50Hz. Push Buttons shall feature a diaphragm seal to protect the button from the entrance of oil , water and other contaminants. O-ring seals, which rely on lubricants, shall not be used.

Start and stop push buttons shall be of shrouded type.

Emergency stop push buttons shall be of maintained contact, pull to reset and lockable at EM-stop to prevent reset. Engraved legend plates shall be fitted with all push buttons.

12.3 Selector switches:

Selector switches shall be positive action rotary can switches, which shall incorporate double break contacts. Selector contacts shall be double break and of hard silver alloy.

They shall have a minimum continues current rating of 10A and be of a high breaking capacity. The switch positions shall be marked on all engraved legend plates, which shall be made from black, white, black traffolyte, and the minimum character size shall be 3 mm. Operating knobs of the rotary type with lever or key operated actuators.

Hands -Off -Auto selector switch shall have three positions with center position as off.

13.0 Site condition:

Altitude : Sea level

Relative Humidity : 100%

Design ambient temperature : 50 deg. C

Surface temperature : Solar radiation may increase surface Temperature up to 80 deg. C.

Rainfall : 54.4 mm maximum per day.

Atmosphere : Salipherous atmosphere often containing fine dust and pollutants in particular CO2 and H2S.

14.0 Codes and Standards:

IEC 38 Standard voltages

IEC 50 International Electro technical Vocabulary.

IEC 51 Recommendations for indicating electrical measuring instruments IEC 59 Standard current ratings

BSEN 60947-2

IEC 947-2 Air Circuit Breaker/ Moulded Case Circuit Breakers.

IEC 158 Low voltage control gear

IEC 408 Low voltage air break switches, air break disconnectors, air break switch disconnectors and fuse combination units.

IEC 439-1 Factory built assemblies of low voltage switchgear and controlgear BS EN 61439-1

IEC 445 Identification of equipment terminals and of termination of certain conductors, including general rules of alphanumeric system.

IEC 446 Identification of insulated and bare conductor by colors IEC 529 Classification of degrees of protection provided by enclosures.

IEC 898 Miniature Circuit Breaker.

(The equivalent British standards for the above IEC specifications shall also apply)