Section 110.26 is divided into six subsections identified as (A) through (F). Section 110.26(A) defines the required height, width and depth of working space according to the voltage and type of equipment being considered
Height of working space is measured from the grade, floor, or platform, and is required to be at least 6.5 feet or the height of the equipment, whichever is greater. If there is electrical equipment that is associated with the electrical system located above or below a piece of equipment, it is allowed to extend no more than 6 inches into the required working space.
There are two exceptions to the base requirement for height of working space.
The first is for existing dwelling units, where panelboards, or service equipment, that do not exceed 200 amperes are allowed in working space that is less than 6.5 feet.
The second exception is new to the 2011 NEC and states that meters that are installed in meter sockets shall be permitted to extend beyond the other equipment, but the meter socket is still required to follow the rules of this section.