Sensing devices must be between which inches?

• A. 1/4 to 1/2 inch
• B. 1/8 to 1/4 inch
• C. 3/8 to 3/4 inch
• D. 1/2 to 1 inch

Answer: (C)

Sensing devices are kept a precise clearance from the moving surface so they reliably detect when the step and surrounding area are in the correct position and can trigger the safety system without nuisance trips or missed detections. The 3/8 to 3/4 inch range balances sensitivity with durability: it’s close enough to respond promptly to a condition that could affect safety, but far enough to tolerate normal wear, debris, and manufacturing or installation tolerances. If the gap is smaller than 3/8 inch, wear or contact could cause binding or false triggering; if it’s larger than 3/4 inch, the sensor might not sense a required condition in time, compromising safety. This is why the specified range is used.