NO and NC (Normally Open and Normally Closed) describe the resting state of a switch or relay contact, referring to whether it allows current to flow when not actively switched. They are crucial components in electrical circuits and PLC (Programmable Logic Controller) programming for controlling how devices respond to switch actions.

Here's a breakdown of their functions:

• Normally Open (NO):

• In its natural state, the contact remains open, acting like a broken wire.
• Current cannot flow through the circuit until the switch is activated.
• Imagine a light switch on a wall. When it's off (normal state), the circuit is open, and the light is off. Flipping the switch (activation) closes the circuit and allows current to flow, turning on the light.

• Normally Closed (NC):

• In its resting state, the contact is closed, similar to a completed circuit.
• Current can flow freely through the circuit.
• When the switch is activated, the contact opens, interrupting the current flow.
• An analogy would be a button used to turn off a light already on. The button acts like an NC contact - normally allowing current to flow (light on), and pressing it (activation) breaks the circuit and cuts power.

Why are NO and NC important?

• Versatility in Circuit Design: They provide flexibility to create circuits that respond differently to switch activation.

• NO switches are ideal for turning things on (like lights with a wall switch).
• NC switches are useful for safety shut-off mechanisms (e.g., emergency stop buttons) or preventing malfunctions (like ensuring a machine door is closed before starting).

• Logic Building in PLC Programs: By combining NO and NC contacts with other elements like timers and counters, you can design complex control systems for industrial automation. They allow you to define specific conditions for activating various functions.

By understanding NO and NC, you can design circuits and PLC programs that precisely control how devices behave based on switch interactions.