2002 NEC 110.26(A)(3) Height of Working Space.
The work space shall be clear and extend from the grade, floor, or platform to the
height required by 110.26(E).
Here's the rule: Within the height requirements of this section, other equipment that is associated with the electrical installation and is located above or below
the electrical equipment shall be permitted to extend not more than 150 mm (6 in.) beyond the front of the electrical equipment.