Nace CP 1, Course Manual

Page: 390 / 535

RP0177-2000
12 NACE International
structures. The person must also know the hazards
of the construction equipment being used as related
to the “limit-of-the-approach” regulations governing
them.
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The person shall be furnished with the
instrumentation, equipment, and authority required to
implement and maintain safe working conditions.
5.3.2 The AC potential difference between a
structure and the earth can be substantially reduced
by appropriate grounding procedures. The AC
potential difference between structures can be
reduced by appropriate bonding procedures. The AC
potential difference between separate points in the
earth can be reduced through the use of appropriate
grounding grids. The grounding or bonding
procedure for safe construction activities depends
upon the type, magnitude, and duration of the AC
exposure. Each situation shall be analyzed by a
competent person, and safe operating procedures
shall be employed during the entire construction
operation.
5.3.3 During the construction of metallic structures
in areas of AC influence, the following minimum
protective requirements are prescribed:
(a) On long, metallic structures paralleling AC
power systems, temporary electrical grounds
shall be used at intervals not greater than 300 m
(1,000 ft), with the first ground installed at the
beginning of the section. Under certain
conditions, a ground may be required on
individual structure joints or sections before
handling.
(b) All temporary grounding connections shall
be left in place until immediately prior to
backfilling. Sufficient temporary grounds shall
be maintained on each portion of the structure
until adequate permanent grounding connections
have been made.
5.3.4 Temporary grounding connections may be
made to ground rods, bare pipe casing, or other
appropriate grounds. These temporary grounding
facilities are intended to reduce AC potentials. Direct
connections made to the electrical utility’s grounding
system during construction could increase the
probability of a hazard during switching surges,
lightning strikes, or fault conditions, and may
intensify normal steady state effects if the grounding
system is carrying AC; such connections should be
avoided when possible.
5.3.5 Cables used for bonding or for connections to
grounding facilities shall have good mechanical
strength and adequate conductivity. As a minimum,
copper conductor 35-mm
2
(0.054-in.
2
) (No. 2 AWG)
stranded welding cable or equivalent is
recommended. See Table 1 and Figures 1, 2, and 3
for cable sizes adequate to conduct the anticipated
fault current safely.
5.3.6 Temporary cable connections to the affected
structure and to the grounding facilities shall be
securely made with clamps that apply firm pressure
and have a current-carrying capacity equal to or
greater than that of the grounding conductor.
Clamps shall be installed so that they cannot be
accidentally dislodged.
5.3.7 All permanent cable connections shall be
thoroughly checked to ensure that they are
mechanically and electrically sound and properly
coated prior to backfilling.
5.3.8 The grounding cable shall first be attached to
the grounding facilities and then securely attached to
the affected structure. Removal shall be in reverse
order. Properly insulated tools or electrical safety
gloves shall also be used to minimize the shock
hazards. THE END CONNECTED TO THE
GROUND SHALL BE REMOVED LAST.
5.3.8.1 In those instances in which high power
levels are anticipated in the bonding cable, the
following procedure is recommended to prevent
electrical arc burns or physical damage to the
coating or metal on this pipe.
(a) The pipe grounding clamp shall be
connected to the pipeline.
(b) The grounding cable shall be connected
to the grounding facility.
(c) The grounding cable shall be connected
to the grounding clamp on the structure.
5.3.9 All grounding attachments and removals shall
be made by, or under the supervision of, the person
in charge of electrical safety.
5.3.10 If hazardous AC potentials are measured
across an isolating joint or flange, both sides of the
joint or flange shall be grounded and/or bonded
across. If required, a permanent bond shall be made
before the temporary bond is removed.
5.3.11 Before the temporary grounding facilities are
removed, provisions must be made to permanently
control the effects of AC potentials on the affected
structure. These provisions depend on the type of
cathodic protection, the type of structure, and the
anticipated magnitude of AC potentials.
5.3.12 Vehicles and other construction equipment
are subject to existing electrical safety regulations
when operated in the vicinity of high-voltage AC
lines.
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