Describe circuit-control devices.

Description includes

• construction, number, and location of terminal connections on switches and relays
• operation of switches and relays
• significance of voltage and current ratings
• explanation of abbreviations
• SPST (single pole, single throw)
• SPDT (single pole, double throw)
• DPST (double pole, single throw)
• DPDT (double pole, double throw)
• NO (normally open)
• NC (normally closed)
  
  
• illustration of how to hook up three-way switches for two points of control.

Process/Skill Questions:

• What common circuit-control device is used in most heating, ventilation, and air-conditioning (HVAC) systems?
• What is the significance of voltage and current ratings when replacing control devices?
• How is a DPDT switch identified?