Nace CP 1, Course Manual

Page: 391 / 535

RP0177-2000
NACE International 13
5.3.12.1 Metallic construction sheds or trailers,
fences, or other temporary structures shall be
grounded if subject to AC influence.
5.3.13 The person in charge of electrical safety shall
communicate at least daily with the utility controlling
the involved power lines to ascertain any switching
that might be expected during each work period.
This person may request that reclosing procedures
be suspended during construction hours, and may
explore the possibility of taking the power line out of
service. The person shall also keep informed of any
electrical storm activity that might affect safety on the
work site. The person shall order a discontinuation
of construction during local electrical storms or when
thunder is heard.
5.3.14 The use of electrically isolating materials for
aboveground appurtenances such as vent pipes,
conduits, and test boxes may reduce shock hazards
in specific instances. However, electrical wires
permanently attached to the pipeline, such as
cathodic protection test wires, may have a high
possibility of a shock hazard because they cannot be
isolated from the pipe (see Paragraph 7.2.6).
5.4 Operations and Maintenance
5.4.1 Maintenance of structures and cathodic
protection facilities under conditions that include AC
potentials may require special precautions. Warning
signs shall be used as a minimum precaution. All
maintenance shall be performed by or under the
supervision of a person familiar with the possible
hazards involved. Personnel must be informed of
these hazards and of the safety procedures to follow.
5.4.2 Testing of devices intended to limit AC
potentials shall be in accordance with manufacturer’s
recommendations and performed under the
supervision of a person familiar with the possible
hazards involved. In those areas where the presence
of combustible vapors is suspected, tests must be
conducted before connections are made or broken to
determine that the combustible vapor level is within
safe limits. No more than one device intended to
limit the AC potential should be disconnected at any
one time. When a single protective device is to be
installed, a temporary shunt bond, with or without
another decoupling device, must be established prior
to removing the unit for service.
5.4.3 Testing of cathodic protection systems under
the influence of AC potentials must be performed by
or under the supervision of a qualified person. In all
cases, tests to detect AC potentials shall be
performed first, and the structure shall be treated as
a live electrical conductor until proven otherwise.
Cathodic protection records should include the
results of these tests.
5.4.4 Test stations for cathodic protection systems
on structures that may be subject to AC potentials
shall have dead-front construction to reduce the
possibility of contacting energized test leads. Test
stations employing metallic pipes for support must
be of dead-front construction.
5.4.5 Safe work practices must include attaching all
test leads to the instruments first and then to the
structure to be tested. Leads must be removed from
the structure first and from the instruments last.
5.4.6 When structures subject to AC influence are
exposed for the purpose of cutting, tapping, or
separating, tests shall be made to determine AC
potentials or current to ground. In the event that
potentials or currents greater than those permitted by
Paragraph 5.2 are found, appropriate remedial
measures shall be taken to reduce the AC effects to
a safe level. In the event this cannot be achieved,
the structure shall be regarded as a live electrical
conductor and treated accordingly. Solid bonding
across the point to be cut or the section to be
removed shall be established prior to separation,
using as a minimum the cable and clamps outlined in
Paragraphs 5.3.5 and 5.3.6.
5.4.7 On facilities carrying combustible liquids or
gases, safe operating procedures require that
bonding across the sections to be separated precede
structure separation, regardless of the presence of
AC.
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Section 6: AC and Corrosion Control Considerations
6.1 Introduction
6.1.1 This section recommends practices for
determining the level of AC influence and lightning
effects to which an existing metallic structure may be
subjected. This section also outlines several points
for consideration regarding the effects these
potentials may have on corrosion control systems
and associated equipment.
6.2 Determination of AC Influence and Lightning Effects
6.2.1 A cathodic protection system design should
include an evaluation to estimate the level of AC