Electrical Schematics and Controls Flashcards

In a ladder diagram, what does a normally closed (NC) contact symbol represent?

Answer: A contact that is closed during normal de-energized state

A normally closed contact is closed (conducting) when the coil controlling it is de-energized, and opens when the coil is energized.

What is the purpose of a time-delay relay (TDR) in an AC system schematic?

Answer: To prevent short cycling by delaying compressor restart

A time-delay relay prevents short cycling by enforcing a minimum off-time before allowing the compressor to restart, protecting it from damage.

On a wiring diagram, a dashed line connecting two components typically indicates:

Answer: A mechanical linkage or enclosed assembly boundary

Dashed lines on wiring diagrams typically represent mechanical linkages between components or indicate that components are housed within the same enclosure.

Which control component in a residential AC system senses indoor temperature and signals the system to cycle on or off?

Answer: Thermostat

The thermostat senses indoor ambient temperature and sends a low-voltage signal to the control circuit to energize or de-energize the system.

A dual-voltage motor wired for 240V operation will have its internal windings connected in:

Answer: Series

For 240V operation, the windings of a dual-voltage motor are connected in series, while for 120V they are connected in parallel.

What does the symbol for a fuse look like on a standard electrical schematic?

Answer: A rectangle with a wavy line or S-curve inside

A fuse is represented on schematics as a rectangle containing a wavy or S-shaped line, symbolizing the fusible element inside.

In an AC control schematic, the R and C terminals on a thermostat typically represent:

Answer: Red wire and common ground for 24V control circuit

R is the 24V power supply (red wire) from the transformer secondary, and C is the common return, completing the 24V control circuit.