AND OR

The AND Rung

The AND is a basic fundamental logic condition that is easy to directly represent in Ladder Logic.
Ladder Logic Rung AND
Suppose a switch is wired to Switch1, a second switch is wired to Switch2, and a light bulb is wired through Light1 in such a way that the light is OFF when Light1 is OFF, and ON when Light1 is ON.

In order for Light1 to turn ON, Switch1 must be ON, AND Switch2 must be ON.

If Switch1 is OFF, power (logic) flow from the left rail, but stops at Switch1. Light1 will be OFF regardless of the state of Switch2.

If Switch1 is ON, power makes it to Switch2. If Switch2 is OFF, power cannot flow any further to the right, and Light1 is OFF.

If Switch1 is ON, AND Switch2 is ON – power flows to Light1 solving its state to ON.

The OR Rung

The OR is a logical condition that is easy to represent in Ladder Logic.

Ladder Logic Rung OR logic Suppose a switch is wired to Switch1, a second switch is wired to Switch2, and a light bulb is wired through Light1 in such a way that the light is OFF when Light1 is OFF, and ON when Light1 is ON. In this instance, we want to the light to turn ON if either Switch1 OR Switch2 is ON.

If Switch1 is ON – power flows to Light1 turning it ON.

If Switch2 is ON – power flows through the Switch2 contact, and up the rail to Light1 – turning it ON.

If Switch1 AND Switch 2 are ON – Light1 is ON.

The only way Light1 is OFF is if Switch1 AND Switch2 are OFF.