In basic concept, all low voltage switchgear assemblies incorporating circuit-breakers are of the metalclad type in accordance with the definition of the term ‘metalclad’ outlined for 3.3 kV and 11 kV equipment. Thus, this mechanism can be of advantage in installations where the provision of a heavy battery source of supply could present a problem - technically and/or economically. Whilst both types are equally acceptable from the point of view of performance, the latter, although of somewhat greater complication constructionally, does not require the provision of a relatively heavy DC closing supply. Where required for a triple-pole and neutral installation, the neutral connection is established through a bolted link.Ĭircuit-breaker operating mechanisms are of the dependent power solenoid or stored-energy motor chargedspring type, complying basically with the requirements outlined for 3.3 kV and 11 kV equipment. īreaking a current equivalent to 100% of the symmetrical breaking current applied to an outer pole, without the unbalance forces produced under these conditions adversely affecting correct operation.Ī rated asymmetrical breaking current equivalent to the rated symmetrical breaking current plus, in one phase at the instant of contact separation, a DC component of not less than 50% of the AC component in that phase (see Fig 5.24).Circuit-breakers are specified basically to BS4752: Part 1, but with the following additional capabilities:

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