6.2 Control Relays

Describe a control relay and identify its purpose in an electrically controlled system

Describe the similarities and differences between a contactor and a control relay

Describe the keyed base associated with an ice cube relay and identify advantages of using keyed bases.

Draw the NEMA schematic symbol for a control relay with a coil, two NO SPST contacts, and two NC SPST contacts

Draw the NEMA schematic symbol for a control relay with a coil and two SPDT C form/transfer contacts

Draw the IEC schematic symbol for a control relay with a coil and two SPDT C form/transfer contacts

Number the terminals of the above control relays

Describe a solenoid and discuss its function and purpose inside a control relay

Describe the components of a control relay and identify their purpose

Define and differentiate between rated voltage, pickup voltage, hold in voltage, and dropout voltage

Describe why a 120V AC coil cannot be used with 24V DC

Differentiate between inrush and sealed in current

Describe why a means of voltage spike suppression must be used for certain coils

Discuss points of inspection and maintenance procedures for control relays

Describe the purpose of bifurcated or split contacts in a control relay

Differentiate between make, break, and continuous current carrying capacity

Describe a solid state relay in general terms

Discuss the PLC and its relation to the control relay (comment at 25:40)

BONUS: Describe the behavior of this ladder logic diagram making use of a control relay and its associated contacts for the following sequence of actions:

both STOP and START in their deactivated state

operator presses and releases START

operator presses and releases STOP