4.6 ISOLATING SWITCHES
Isolating switches or switch-disconnector shall be of metalclad type and conform fully to IEC 60947-1 and 60947-3. They shall be able to operate continuously at full current rating without de-rating, capable of making and breaking currents under normal condition and when in open position, providing isolation from source of electrical energy for reasons of safety. They shall be quick-make, quick-break type suitable for use on 240/415 V, 50 Hz. a.c. system. The enclosure shall comprise of heavy gauge steel plates rustprotected and finished grey stove enamel.
Front access doors, which is detachable, shall be fitted with dust-excluding gasket and shall be interlocked to prevent opening when the switch is ‘ON’. However this interlock shall be able to be defeated by competent person for maintenance purpose. They shall be provided with removable top and bottom end plates or knockouts for cable entry. The enclosure, the isolating mechanism and all other accessories shall be from the same manufacturer. They shall be provided with, if required,facilities for lock-on and lock-off the operating handle.