Q. What is the required working space for an installation of an electric sign transformer, ballast, or power supply located above a suspended ceiling? The location is such that it is considered to be accessible. The equipment is securely fastened in place, independent of the suspended ceiling grid.
A) Three feet in the direction of access, 2 feet – 6 inches wide, and 6 feet – 6 inches high.
B) Three feet in the direction of access, 3 feet wide, and 3 feet high.
C) 3 feet – 6 inches in the direction of access, 3 feet wide, and 6 feet – 6 inches high.
D) Sufficient access and working space is all that is required for this installation.

Answer: B
In this example, rather than using the general requirements of 110.26, it is appropriate to use the specific requirements of 600.21(D) and (F). Section 600.21(D) makes it clear that the 3 feet by 3 feet by 3 feet space is the requirement for the clear, unobstructed working space in this particular situation.

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 necexpert@aol.com.