ELE 146 Class 5: Control Relays and Motor Starters

Vocabulary practice flashcards covering contactor operation, control relays, overload protection, two-wire control, three-wire control, and seal-in logic from ELE 146 Class 5.

Power circuit

The circuit that carries energy and motor current, consisting of line power ($L1, L2, L3$), contactor main contacts ($F$), overload elements ($O.L.$), and the motor terminals ($T1, T2, T3$).

Control circuit

The circuit that carries control current to provide permission for when the power contacts close, consisting of STOP and START pushbuttons, the contactor coil, the overload control contact, and an auxiliary seal-in contact.

Control relay

A logic device that uses an electromagnetic coil to change the state of its contacts to switch small control loads, such as pilot lights, timer coils, and relay coils.

Contactor

A motor-duty power-switching device built to switch motor current on the power side when its coil is energized by the control circuit.

Normally Open (NO)

A contact state describing contacts that remain open in their normal, unactuated state and close when the associated device or coil is energized or actuated.

Normally Closed (NC)

A contact state describing contacts that remain closed in their normal, unactuated state and open to break the electrical path when the physical device or coil is actuated.

NC contact open

The graphical representation depicting a Normally Closed contact whose conductive path has been physically opened by actuation.

Two-wire control

A control method using a maintained command device, such as a selector switch, which stays in the RUN position and may cause the motor to restart automatically when power is restored after an outage.

Three-wire control

A control method utilizing momentary START and STOP pushbuttons paired with an auxiliary seal-in contact for memory, which prevents the motor from restarting automatically after power loss.

Seal-in contact

A Normally Open auxiliary contact connected in parallel around the momentary START pushbutton that closes when the contactor coil energizes, maintaining current to the coil after START is released.

Stop dominance

A design configuration placing the Normally Closed STOP pushbutton in the common series path ahead of the START and seal-in branch, ensuring the coil drops out whenever STOP opens regardless of the START branch condition.

Overload elements (O.L.)

Power-side sensing devices connected in series with each phase line to monitor and detect excessive motor current.

Overload control contact

A control-side Normally Closed contact (terminals 95-96) on the overload relay that opens when an overload trips, de-energizing the contactor coil and shutting off the motor.

Three-Wire Motor Control Circuit (Amatrol Figure 5-2)

The authoritative lab wiring diagram featuring a top three-phase motor power circuit, a middle control transformer and fuse section, and a bottom three-wire START/STOP ladder control circuit.