Nace CP 1, Course Manual

Page: 514 / 535

TM0101-2001
NACE International 3
Test Lead: A wire or cable attached to a structure for
connection of a test instrument to make cathodic protection
potential or current measurements.
UST System: Underground Storage Tank System. See
Tank System.
Voltage: An electromotive force or a difference in electrode
potentials expressed in V.
Voltage Drop: The voltage across a resistance according
to Ohm's law.
Wire: A slender rod or filament of drawn metal. In practice,
the term is also used for smaller-gauge conductors (size 6
mm
2
[0.009 in.
2
] [No. 10 American Wire Gauge {AWG}] or
smaller).
________________________________________________________________________
Section 3: Safety Considerations
3.1 Personnel who install, adjust, repair, remove, or test
impressed
current protection equipment shall be
knowledgeable and qualified in electrical safety precautions
before work is begun. The following procedures shall be
implemented when electrical measurements are made:
3.1.1 Use properly insulated test lead clips and
terminals to avoid contact with an unanticipated high
voltage (HV). Attach test clips one at a time using a
single-hand technique for each connection.
3.1.2 Use caution when long test leads are extended
near overhead high-voltage alternating current (HVAC)
power lines, which can induce hazardous voltages onto
the test leads. Refer to NACE Standard RP0177
2
for
additional information about electrical safety.
3.1.3 Use caution when making tests at electrical
isolation devices. Before proceeding with further tests,
use appropriate voltage detection instruments or
voltmeters with insulated test leads to determine
whether hazardous voltages exist.
3.1.4 Avoid testing when thunderstorms are in the
area.
3.1.5 Use caution when opening manways and when
stringing test leads across streets, roads, and other
locations subject to vehicular and pedestrian traffic.
When conditions warrant, use appropriate barricades,
flagging, and/or flag persons.
3.1.6 Before entering excavations and confined
spaces, inspect these areas to determine whether they
are
safe. Inspections may include shoring
requirements for excavations and testing for hazardous
atmospheres in confined spaces.
3.1.7 Observe appropriate electrical codes and
applicable safety regulations.
________________________________________________________________________
Section 4: Instrumentation and Measurement Guidelines
4.1 Electrical measurements of cathodic protection
systems require the proper selection and use of
instruments. Determining tank-to-electrolyte potential,
voltage drop, potential difference, and similar
measurements requires instruments that have appropriate
voltage ranges. The user should know the capabilities and
limitations of the equipment, follow the manufacturer's
instruction manual, and be skilled in the use of electrical
instruments. Failure to select and use instruments correctly
causes errors in cathodic protection measurements.
4.1.1 Analog instruments are usually specified in
terms of input resistance or internal resistance. This is
usually expressed as ohms/volt (
ÿ
/V) of full-scale
meter deflection.
4.1.2 Digital instruments are usually specified in terms
of input impedance expressed as megohms.
4.2 Factors that may influence instrument selection for field
testing include:
(a) Input impedance (digital instruments);
(b) Input
resistance or internal resistance (analog
instruments);
(c) Sensitivity;
(d) Conversion speed of analog-to-digital converters used
in digital or data-logging instruments;
(e) Accuracy;
(f)
Instrument resolution;
(g) Ruggedness;
(h) Alternating current (AC) and radio frequency (RF)
signal rejection; and
(i)
Temperature and/or climate limitations.
4.2.1 Digital instruments are capable of measuring
and processing voltage readings many times per
second. Evaluation of the input waveform processing
may be required if an instrument does not give
consistent results.
4.2.2 Measurement of tank-to-electrolyte potentials on
tanks or systems affected by dynamic stray currents