All switchgears shall have voltage and frequency rating suitable for the power system to which they are connected to. The current rating shall not be less than that specified in the Drawings and/or Bill of Quantities. They shall conform to the latest relevant IEC Standards.
5.1 MOULDED CASE CIRCUIT BREAKERS
Moulded case circuit breakers (mccb) shall have the number of poles as specified in the Drawings and/or Bill of Quantities. They shall comply with IEC 60947-1 and IEC 60947-2. They shall be fully tropicalised and suitable to be used up to an ambient temperature of 40 0C, enclosed in glass-reinforced polyester moulded case and suitable for use on 240/415 V, 50 Hz. a.c. supply system.
They shall be of the quick-make, quick-break type having manually operable toggle type handle. Permanent position indicators shall be provided to show status of the breaker. When tripping occurs, the handle shall be in the `trip’ position midway between the ‘OFF’ and ‘ON’ or ‘Ο’ and ‘|’ position so as to provide positive indication of automatic interruption. The operating mechanism shall be non-tamperable.
The mccb shall have trip-free feature to prevent the breaker from being closed against fault conditions. Multipole mccb shall have common-trip operating mechanism for simultaneous operation of all poles.The tripping units shall be of thermal-magnetic type with bimetallic elements for inverse time-delay overload protection and magnetic elements for short circuit protection. An arc extinguisher shall be incorporated to confine, divide and extinguish the arc drawn between the breaker contacts each time a breaker interrupts current.
The contacts shall be of non-welding type. Unless otherwise specified in the Drawings and/or Bill of Quantities, the minimum a.c. interrupting capacity of the mccb shall be 50 kA rms (symmetrical) for 1 second at 415 V. The rated service short-circuit breaking capacity (Ics) of the mccb shall be 100% of the rated ultimate short-circuit breaking capacity (Icu) at 415 volts. Unless otherwise specified in the Drawings and/or Bill of Quantities, the minimum continuous current ratings for the mccb shall be of 155 % of the rated capacitor currents.
5.2 SWITCHING CONTACTORS
The switching contactors shall comply with IEC 60947-4-1 and shall be of utilization category AC-6B rated for switching low inductance capacitors. They shall be fully tropicalised, suitable for use on 240/415 V, 50 Hz. a.c. system.
The operating coil shall be 240 V 50 Hz. a.c. type and shall operate satisfactorily when the voltage at the coil terminals is between 85% and 110% of the nominal voltage. The electro-magnet shall be of laminated type.
Unless otherwise specified in the Drawing and/or Bill of Quantities, the minimum continuous current ratings for the switching contactors and the connection cables shall be of minimum 135 % of rated capacitor currents.