JANUARY 31 2003
earth with a backhoe or bulldozer. This method can also be used to simulate a deeper
installation. It is possible to install 9 to 18 meters (30 to 60 feet) in this manner if there
are no rock formations.
CAUTION: Do not connect the structure being tested to the positive terminal of the
power source. Severe corrosion of the structure may result.
Connections. The temporary anodes all must be connected to the power
source positive terminal. The structure being tested must be connected to the negative
terminal. For physical strength and low resistance, #6 AWG copper cable or larger
must be used and #2 AWG or greater is desired, especially if long runs in either the
structure or anode cable are needed. Connections can be made with pipe clamps, test
clamps of sufficient size, split bolts, and exothermic welding. All wire and connections
must be made to accommodate the voltage and current required for the testing. The
normal portable rectifier is 60 volts at 30 amps or 30 volts at 60 amps. Other rectifiers
may be over 180 volts or 100 amps.
Before Applying Power. Before any power is applied, it is essential to
obtain the as-found potential data of the structure. The native potential must be tested
for all locations to be tested during the current requirement test, to obtain the potential
shift accomplished by the test current.
Applying Power. Beginning at a low voltage setting, turn power on, ensure
the potential shift of the structure is in the negative direction. Gradually increase
voltage and current to desired output, while periodically checking potential to ensure a
corresponding negative shift as current is increased. If maximum voltage is reached
and more current is still required, turn system off and supplement the temporary anode
bed (paragraph 7-10.4).
Sufficient Current. Sufficient current is applied when a substantial section
of the structure to be tested has achieved a noticeable potential shift or when full
protection is achieved. If full protection is achieved, the current requirement is the same
as the test current. If full protection is not achieved, further calculations are required.
Calculating Current Requirements. Once the potential shift is ascertained,
and the current to get that shift is known, the current requirement can be calculated. If
the current is doubled, the potential shift is doubled. Current distribution should be
considered: If good current distribution is achieved, a simple mathematical formula will
produce the current requirement. If proper current distribution is not achieved, it must
be designed into the system. If the design will call for a deeper anode bed, current
requirement can be estimated by calculations. If the design is for surface beds,
additional cathodic protection systems should be considered and further current
requirement testing for additional locations conducted.