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Contactor Interlocked Auto change over Vs Motorized MCCB Change Over

Nick Parker

The distribution board gets power from two UPS and I'm planning to install a Auto change over system. (Break before make)

Since the loads are critical (but can accept a short time interruption), which is beneficial? Contactor Interlocked Auto change over (or) Motorized MCCB Change Over

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    I see both of these solutions used, with various advantages/disadvantages once fail modes are considered:-

    Contactor - fail safe power off, cannot be manually switched (this could be good or bad, depends on use). Of course everything can be overidden so I have seen these wedged in.....

    MCCB - fails into static position leaving one supply potentially connected, can be manually overidden (also good or bad!)

    So it all comes down to the use/load. Power off is good from a safety point of view on a non-critical load or where it may be abused (eg factory). Power left on may be good if the load is critical even with control system broken (eg hospital, pumping station).

    If you really care about the supply then you also install a manual bypass around the changeover :-)

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