XIO stands for Examine If Open. What happens to its contact when the input is energized?

• A. The contact closes and allows current
• B. The contact opens and blocks current
• C. The contact toggles
• D. The contact remains unchanged

Answer: (B)

XIO, Examine If Open, represents an inverted input condition. The contact behaves like a normally closed path that opens when its input is energized. So when the input is energized, the XIO contact opens, breaking the circuit and preventing current from flowing through that part of the rung. If the input isn’t energized, the contact stays closed and would allow current to pass (assuming the rest of the rung is satisfied). This inversion is why XIO is used to detect when an input is not active.