JANUARY 31 2003
negative lead of the multimeter, locate the point of highest voltage on the surface of the
ground (this will be directly over an anode). Repeat by locating all operational anodes.
Mark each anode found and compare to system drawings. Starting in a straight line 3
meters (10 feet) from the first anode, perform a potential test every 0.6 meters (two feet)
over the entire length of the anode bed, to a point 3 meters (10 feet) past where the last
anode is (or is suppose to be) located. Using graph paper, and using vertical lines to
represent the measured potentials, and horizontal lines to represent the 0.6-meter (two-
foot) intervals, graph all readings. This will show the condition of all anodes, and will
indicate if a broken header cable (anode lead) or failed anodes exist. It will show a
broken cable between functional and non-functional anodes. If anodes are failing, the
gradients will peak differently, or the gradients will fall, then rise intermittently.
If no anodes are operational, use the fault detector and cable locator,
connected directly to the anode cable P4, to trace the anode lead from the rectifier
towards the anode bed. This can be extremely difficult in some cases. An alternative
method is to locate the first anode (from drawings, markers, or induction methods).
Excavate to the first anode and measure continuity back to the rectifier using a cathodic
protection Multi-Combination meter continuity check circuit. Use the fault detector and
cable locator, connected directly to the anode to trace the anode lead from the anode
towards the rectifier. If this is still unsuccessful, replace the anode lead from the rectifier
to the anode.
When using the direct connection method,
it is essential
isolated ground for the fault detector or cable locator to put a strong locator signal on
the cable under test.
Rectifier Taps. Measure the AC voltage on the taps of the rectifier with a
handheld multimeter on the AC volt scale. Remove the tap bars or shorting wires.
Measure the voltage from F5 to F4, F4 to F3, F3 to F2, F2 to F1, and F1 to C1. All
readings should be approximately the same. Measure the voltage from C5 to C4, C4 to
C3, C3 to C2, C2 to C1. All readings should be approximately the same. Any lead that
tests different must be checked for connection (proceed to paragraph 5-2.9.1).
Note: On some rectifiers, F1 to C1 may be a unique voltage.
With power OFF, check for loose connections from F1 through F5 and C1
through C5, including any tap bar or shorting wire, and continuity of all wires between
those points. Note that loose connections are characterized by heat, discoloration of
the connection, and melted insulation. Repair or replace loose connections and replace
damaged or broken wires, if possible. If only one tap is inoperative, a different tap
setting may be operational, and testing will reveal functioning taps. If replacement of
wire is not possible, replace the transformer. If no problems are found, proceed with 5-