What is a control relay and how does it contribute to sequencing in a control circuit?

• A. A relay used to control circuits and provide logic, interlocks, and sequencing of operations.
• B. A device that stores energy for starting motors.
• C. A resistor used for current limiting.
• D. A switch that opens when temperature rises.

Answer: (A)

A control relay is a device that uses an electromagnet coil to operate a set of contacts, turning a control circuit into logic that drives other equipment. When the coil is energized, its contacts change state (normally open contacts close, normally closed contacts open), creating control paths that start, stop, or interlock downstream devices. This allows you to build sequencing in a control circuit by wiring multiple relay contacts in series or parallel to define the order of operations, using one relay to enable the next, and adding latch or hold-in contacts to maintain a state until a reset occurs. For example, energizing a first relay can feed the next relay’s coil, which then progresses the sequence, while an interlock contact prevents unsafe simultaneous actions. The other options describe components with different roles—storing energy to start motors, limiting current, or sensing temperature—so they don’t convey how a relay provides logic and sequencing in control circuits.