Automatic Transfer Switches – Tech Corner


Often times, a transfer switch specification will include the language “quick-make, quick-break”.  So how does this relate to circuit breakers and contactors?

Eaton’s molded case circuit breaker (MCCB) design employs a quick-break, quick-make or overcenter-toggle mechanism, meaning that it opens and closes the contacts at a specific, over-center point during the travel path of the operating handle. The rate at which the contacts close or open is independent of handle speed and prevents the operator from inadvertently holding the contacts in a slightly separated position.  You’ve probably experienced this same behavior when opening or closing a breaker in the loadcenter panel of your home.

A Magnum Power Breaker differs from a MCCB design by using pushbutton control but it too also employs a quick-break, quick-make mechanism.

With regard to Eaton’s contactor design, it is not of the quick-break, quick-make type and uses a selonoid (rather than spring action) to electrically close and open contacts.


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