From the 2008 NEC. (underlining is mine)
110.26 Spaces About Electrical Equipment.
- - (F) Dedicated Equipment Space.
All switchboards, panelboards, distribution boards, and motor control centers
shall be located in dedicated spaces and protected from damage.
- - -
Exception: Control equipment that by its very nature or because of other rules
of the Code must be adjacent to or within sight of its operating machinery shall
be permitted in those locations.
- - - (1) Indoor. Indoor installations
shall comply with 110.26(F)(1)(a) through (F)(1)(d).
- - - - (a)
Dedicated Electrical Space. The space equal to the width and depth of the
equipment and extending from the floor to a height of 1.8 m (6 ft) above the
equipment or to the structural ceiling, whichever is lower, shall be dedicated
to the electrical installation. No piping, ducts, leak protection apparatus, or
other equipment foreign to the electrical installation shall be located in this
- - - - - Exception: Suspended ceilings with removable panels
shall be permitted within the 1.8-m (6-ft) zone.
- - - - (b) Foreign
Systems. The area above the dedicated space required by 110.26(F)(1)(a) shall be
permitted to contain foreign systems, provided protection is installed to avoid
damage to the electrical equipment from condensation, leaks, or breaks in such
- - - - (c) Sprinkler Protection. Sprinkler protection
shall be permitted for the dedicated space where the piping complies with this
- - - - (d) Suspended Ceilings. A dropped, suspended, or similar
ceiling that does not add strength to the building structure shall not be
considered a structural ceiling.
- - - (2) Outdoor. Outdoor electrical
equipment shall be installed in suitable enclosures and shall be protected from
accidental contact by unauthorized personnel, or by vehicular traffic, or by
accidental spillage or leakage from piping systems. The working clearance space
shall include the zone described in 110.26(A). No architectural appurtenance or
other equipment shall be located in this