General
The circuit breaker shall be four poles, horizontal draw out type and shall have inherent fault current breaking and making capacity as specified.
Circuit breakers shall be mounted along with its operating mechanism on telescopic rails. The cradle should be so designed and constructed as to permit the smooth withdrawal and insertion of the breaker
into it. The movement should be free of jerks and shall preferably be on rollers and not on the flat surface.
Suitable guides shall be provided to minimize misalignment of the breaker.
There shall be preferable ‘Isolated’ and ‘Maintenance’ positions for the breakers.
Main poles of the circuit breakers shall operate simultaneously in such a way that the maximum difference between the instants of contacts touching during closing shall not exceed half cycle of rated frequency.
The main contacts should be of appropriate Silver alloys. Only Silver plating of the faces shall not be acceptable.
Arcing contacts should be of tungsten base alloy and mere Silver plating of the faces shall not be acceptable. Arcing contacts must be separate from main contacts and one piece butt type contacts shall not be acceptable.
ACB assembly shall be capable of being easily removed for routine inspection of the chutes and contacts.
The moving portion of each circuit breaker shall consist of a three-pole circuit breaker with operating mechanism, primary and secondary disconnecting devices,
Auxiliary switches, position indicators and necessary controls wiring, all mounted on a substantial steel framework, This framework and all metal parts of the moving portion apart from current carrying parts shall, when inserting the circuit breaker into the cubicle, be solidly earthed before the circuit breaker reaches test position, the circuit breaker shall then remain effectively earthed when it is in the cubicle.
All feeders with more than 800 A should have withdrawable ACB type circuit breakers with manually and electrically operated spring charge mechanism.
The A.C.B to have 3 distinct positions.
Fully inserted position.
Test position.
Isolated position.The trip functions to be solid state electronic type and consists of following with LED indication of type of trip.
Setting of base current
Adjustable overcurrent protection with adjustable time delay
Adjustable overload protection with adjustable time delay
Adjustable instantaneous trip
Adjustable ground fault tripTest functions to be provided as a standard on the breaker. The ACB should have following flag indicator.
On/Off indicator
Spring charged/uncharged.
Position indicator for connected, test, isolated position.The ACB should have padlock for locking in the service, test or isolated position. Also the ACB to be lockable in off position.
The busbar to be covered by automatic shutters when the ACB is in withdrawn position.
All mechanical interlocks shall be of preventative type and shall be arranged to prevent malfunction as close as possible to the point at which mechanical force is applied, in order to prevent defeat of the interlocks by distortion of linkages. Electrical interlocks shall also function so as to prevent the closing of the circuit breaker before the interlocking demands are fulfilled.
Mechanical interlocks shall be provided which are designed to prevent:
A closed circuit breaker from being withdrawn or inserted into isolating the contacts.
Tripping by attempted isolation.
The closing of a circuit breaker except when correctly located in service or test position.Circuit breakers of the same current and voltage rating shall be fully interchangeable, both electrically and mechanically. It must be impossible to insert a circuit breaker with lower data into a cubicle with higher data.
The ACB to be complete with the following:
Charging lever for the closing spring.
Pushbutton for elimination of charging level
Indicator for closing spring
On button
Off button
On/Off button
Position stopped release for withdrawable breaker.
Hole for draw-out handle
Padlock loop for locking of breaker in CONNECTED, TEST or ISOLATED position.
Position indicator for Connected, Test or Isolated position.
The On and Off buttons are to be place behind sliding covers which serve to prevent unintentional actuation.
The ACB to be provided with automatic screening which can be padlocked. The screens for incoming and outgoing main terminals can be opened independently of each other.Circuit breaker shall be provided with under voltage release wherever specified.
Provision shall be made to lock the breaker in “Isolated” position.
It shall not be possible to open the board door when the circuit breaker is in ‘CLOSED’ position. Built-in interlock should be provided to prevent closing the breaker being inserted into panel.
Standard
To IEC 947-2 or BS EN 61497-2, suitable for triple pole service and shall have breaking capacity of 50kA symmetrical for 3 seconds at 400V.
Utilisation Category
Type B for partial and full discrimination.
Auxiliary Switch Contacts
Provide contacts with minimum rated operational current of 6A at 230V, 50Hz. Provide at least one spare normally-open and one spare normally-closed contact. Provide shunt trip release coil circuits with an early-make/late-break series connected auxiliary contact.
Protection System
Integral to the circuit breaker, incorporating a solid state protection relay.
Trip Unit: Manual reset.
Compartment
House each circuit breaker in a separated self-contained enclosed subsection module within the assembly.
Locking
Provide for circuit breakers to be padlocked in the open position.
Interlocking
Electrical: Interlock control circuitry of functional units using normally-opened and normally-closed auxiliary contacts.
Mechanical: Required.
Coded key: Captive type with squared face key with alphabetical or numerical coded operating face.
Door Interlocks
Except for compartment doors serving only as covers, provide interlocks preventing compartment doors being open while circuit breakers are closed.
Abnormal Operations
Provide breakers which cannot be used in the following operations:
Slow closing or opening of contacts.
Manual independent hand closure, if springs fail.
Release of charged springs while contacts are closed.Auxiliary contacts: Use contacts which remain connected in the test/isolated position.
Interlocking: Provide interlocking which prevents circuit breaker being racked in or withdrawn unless it is in a tripped condition and prevents the circuit breaker being closed unless located in either the connected or test/isolated position. Provide stored energy devices which are automatically discharged by any racking operation.
Shutters: Provide automatic shutters, which can be padlocked, covering busbar and incoming/outgoing circuit connections and labelled "BUSBARS" and "CIRCUIT" respectively.
Earthing: Provide earthing connection between withdrawable carriage and assembly earth busbar which makes before, and breaks after, other contacts on the circuit breaker carriage.
8.13.2 Moulded Case And Miniature Circuit Breakers General
All MCCB’s protecting outgoing feeder circuits shall be of instantaneous type and shall be designed and constructed to have short circuit breaking capacity as per the calculated kA rating requirement, and shall conform to the requirements, including latest amendments, of IEC 947-2 (BSEN 60947-2) 1992, and shall be fault tested to category P2 (ICS) of these standards.
All MCCB’s shall be of thermal magnetic, manually and automatically operated type and shall be designed to provide positive trip-free operation on abnormal overloads with quick break contacts for both manual and automatic operation. Adequate protection for the stationary and movable contacts shall be provided with effective and rapid arc interrupting devices. An inverse time delay thermal overcurrent trip element and a magnetic instantaneous overcurrent trip element shall be provided on each pole of the breaker for common tripping of all poles.
Residual Current Devices
Provide both overcurrent and earth leakage protection on earth leakage circuit breakers (RCBO’s).
Current operated earth leakage circuit breakers shall be in accordance with BS EN 61008 providing the functions of isolation, switching and earth leakage protection of electrical circuits.
The ELCB’s shall have a residual current operated electro-mechanical release.
The ELCB’s shall incorporate a filtering device to eliminate unwanted tripping due to transient voltage.
A test push button is to prove operation.
A trip free mechanism is required to ensure that the unit cannot be held closed against an earth fault.
Mounting arrangements: same as for single pole miniature circuit breakers.
Earth leakage circuit breakers: in accordance with BS 4293.1 for 6kA minimum interrupting capacity at 400VAC, 50Hz.
Tripping current: 30mA & 100mA.
Mounting
Mount circuit breakers so that the "ON/OFF" and current rating indications are clearly visible with covers or escutcheons in position. Align operating toggles of all circuit breakers in the same plane.
Utilisation Category
Partial or full discrimination required: Type A.
Adjustable Current Settings
General: Provide accessible trip current adjustment after removing escutcheon.
Labels: Provide labels indicating trip settings.
Trip Settings
Adjustable short circuit trip settings: Set to discriminate with upstream and downstream devices using Ipscc.
Trip Units
Circuit breakers with interchangeable and integral trip units: Connect so that trip units are not live when circuit breaker contacts are open.
≥ 250A. Provide solid state protection relay.
< 250A. Thermal magnetic fixed setting acceptable.
Trip Unit: Manual reset.
Locking
Provide for locking circuit breakers in the open position.
Clip Tray Chassis
For miniature overcurrent circuit breakers provide clip tray assemblies capable of accepting single, double, or triple circuit breakers, and related busbars. Provide moulded clip-on pole fillers for unused portions.
Accessories
Rotary handle: Provide "ON/OFF" indication, and override release to open door padlocking facility.
Motor operators: Provide selector switches, controls and indicators.
Auxiliary contacts: Minimum rating 5 A.
8.13.3 Earth Leakage Relay (ELR)
Earth leakage relay (ELR) shall be as shown on the drawings shall be provided in the distribution board. The ELR shall be suitable for operating at temperature ranging between -5°C to 55°C ambient.
Earth leakage relay (ELR) shall comply with the applicable IEC standards.
The ELR shall be modular, compact and din-rail mount design. The ELCB shall be easy clip-on type and shall fit onto the standard din-rail or to the purpose-made brackets inside the distribution board.The ELR shall be suitable for horizontal or vertical mounting.
The ELR shall be protected against nuisance tripping caused by switching surges or lightning surges.The ELR shall be capable of operating in the presence of fault currents with DC components and ELR shall be sensitive to direct component residual currents (Class A).