Symbols and Wiring Diagrams: Contactors and Relays

 Contactors:

• Definition: Mechanical switch linked to a magnetic coil, similar to a solenoid coil.
• Operation: Energized coil pulls electrical contacts together, closing them and allowing current to flow to the load.
• Cutaway View:
  • Control circuit goes to the coil.
  • Line voltage enters the line side, and load side connects to the load.
  • Normally open electrical contacts.
• Side View:
  • Connections at line side (L1, L2, possibly L3 for three-phase).
  • Load side connections (T1, T2, possibly T3 for three-phase).
  • Coil connections can be low or line voltage.
• Typical Contactors: Side and top views, dust covers, safety considerations, and contact position indicators.

Symbols for Contactors:

• Single Pole: Solid bar replaces one set of contacts, used with crankcase heater.
• Double Pole: Two sets of contacts.
• Triple Pole: Three sets of contacts for three-phase motors.
• Symbol Notation: Symbols shown in de-energized position (normally open).

Relays:

• Definition: Contactors rated for 20 AMPS or higher are essentially relays.
• Contact States:
  • Normally Open (NO)
  • Normally Closed (NC)
  • Combination of NO and NC
• Relay Symbols: Shown in de-energized position (no power).

Examples and Symbols:

• Single Pole: NO and NC contacts.
• Double Pole: One NO and one NC contact.
• Triple Pole: Two NC and one NO contact.
• Relay Examples: Schematic of contacts and connections, commonly referred to as "ice cube relays" due to plastic casing.

Visualization:

• Energized Coil: NO contacts close, NC contacts open.
• Examples: Single, double, and triple pole relays changing from normal position when coil is energized.