Q. Is it permissible to run heating/air-conditioning duct 4 feet above a panelboard if the ductwork services the room where the panelboard is located?

A. No. The footprint space (width and depth of the equipment) extending from the floor to a height of 6 feet above the equipment or to the structural ceiling (whichever is lower) must be dedicated for the electrical installation. No piping, duct, or other equipment foreign to the electrical installation can be installed in this dedicated footprint space [110.26(F)].