A distance of at least _____ must be maintained from a nonmetallic conduit containing a high-voltage circuit operating at above 100 Hz.

• A. 1.75 inches
• B. 1.5 inches
• C. 2 inches
• D. 1 inch

Answer: (A)

When high-voltage circuits run through nonmetallic conduit, keeping a safe air gap from nearby surfaces is essential to prevent arcing and tracking along the surface, especially in damp or dusty conditions. For circuits operating above 100 Hz, the specification sets a minimum clearance of 1.75 inches. This distance provides enough dielectric strength at those frequencies and voltages to reduce the risk of an arc forming between the conduit and adjacent surfaces or conductors. The other options fall short of the required minimum (1 inch and 1.5 inches) or are larger than necessary (2 inches) for the minimum standard, so 1.75 inches is the correct minimum.