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 ELECTRICAL
Grounds and Grounding Systems-Continued
dangerously high and current as low as 10 milliamperes may be fatal, extreme care must
be exercised in inspecting and testing ground and grounding systems to minimize danger
of electric shock and possible resulting injury or death. In general, NEVER open a
grounding circuit connection when the equipment it is intended to protect is energized.
This applies equally to grounds on structural or supporting members, to grounds on
equipment enclosures, and to grounds on either primary or secondary system neutrals.
The life and safety of everyone approaching, or coming in contact with, electrical
facilities depends on how carefully and completely inspections of grounds and ground-
ing systems are performed. When equipment is energized, DO NOT make inspection
at bases of electrical equipment, regardless of circuit voltage. Determine if preventive
maintenance inspections are adequate. Check for:
n Visual Connections:
loose, missing, broken connections
signs of burning or overheating
corrosion
rust
frayed cable strands, more than one strand broken in 7-strand cable,
more than 3 strands broken in 19-strand cable
n
Underground Connections:
unsatisfactory condition or defects uncovered when 4 or 5
connections are exposed to view by digging
n Electrical Resistance Tests:
From point of connection on structure, equipment enclosure or
neutral conductor to top of ground rod, allowable resistance can be
obtained from maximum permissive resistance below
From ground rod, mat or network to earth ground, allowable
resistance can be obtained from max. permissive resistance below
From gates to gateposts, allowable resistance is 1/2 ohm
From operating rods and handles of group-operated switches to
supporting structures, allowable resistance is 1/2 ohm
From metallic-cable sheathing to ground rod, cable, or metal
structure, allowable resistance is 1/2 ohm
7-27
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