Fill in the blank with the appropriate answer.

For field-fabricated installations using equipment operating at more than 600V, the minimum air separation between live conductors and between such conductors and adjacent grounded surfaces shall be a minimum of______ in. for an indoor, phase-to-phase application of 13.8kV.

A. 12

B. 7.5

C. 7

D. 5

Answer: B

Section 490.24 of the 2011 NEC lists the requirements for the minimum air separation of field-fabricated installations. The minimum clearance distances are shown in Table 490.24.

Note: The values from Table 490.24 do not apply to interior portions or external terminals of equipment designed, manufactured, and tested in accordance with accepted national standards.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at