What distinguishes machine control relays from general-purpose relays?

Machine control relays are specifically engineered for applications that manage motors or machinery and often operate under more demanding conditions. This distinction means that they can handle higher voltages and currents compared to general-purpose relays, which are typically designed for lighter loads and more general applications.

In addition to their capacity for heavier applications, machine control relays may incorporate features suited for automation and control circuits, such as multiple voltage and current ratings or enhanced durability to withstand regular operation demands. Their construction and specifications reflect the requirements of heavy machinery and industrial automation, which justifies the selection of this answer.

The other options refer to characteristics that don't generally signify a fundamental difference between machine control relays and general-purpose relays. For example, while machine control relays may have multiple configurations, it isn't necessarily true that they are more complex or manual, nor is it accurate to say that they always have fewer contacts than general relays. Thus, the ability to manage heavier loads sets machine control relays apart in terms of design and application capacity.