ERICO Practical Guide to Electrical Grounding - Manual (Page 66)

Practical Guide to Electrical Grounding
GROUNDING
General Provisions - Equipment Fastened in Place. As
noted above, the primary reason equipment and enclosures
are grounded is to provide a low impedance path for
ground-fault current. Such a path helps to ensure that the
overcurrent protective device operates in an effective
manner to protect people and property exposed to ground-
fault currents. Section 250-42 establishes six general
conditions under which exposed noncurrent-carrying metal
parts of fixed equipment likely to be energized must
be grounded:
The first condition requires grounding whenever such metal
parts are located within a zone that extends within 8 feet
(2.4 m) vertically and 5 feet (1.5 m) horizontally of ground
or any grounded objects which may be contacted by
persons. This establishes a reach or touch zone that ensures
protection if persons could come in contact with such
objects.
The second condition requires that any exposed metal parts,
if not isolated, be grounded if installed in wet or damp
locations. The NEC defines a wet location as one which is
subject to saturation with any liquid and other locations
underground or in concrete slabs. Damp locations are those
locations subject to moderate degrees of moisture such as
partially protected outdoor locations and some basements.
The third condition requires grounding of metal parts when
in electrical contact with metal.
The fourth condition covers grounding in hazardous
locations. These high-risk locations are covered in Articles
58
Fig. 3-22
Fig. 3-23
Silicon Bronze Stud, With
2 S.B. Nuts And Washers.
CADWELD Type GL
Copper
CADWELD Type HX
Fig. 3-24
Fig. 3-25
Grounding Book 4/14/99 10/5/99 6:01 PM Page 58 (Black plate)