JANUARY 31 2003
Diodes. Check the diodes/selenium plates of the rectifier with a handheld
multimeter on the diode check scale. With power OFF, remove the tap bars or shorting
wires and the anode lead (P4) and/or the structure lead (N4). Check the diode/selenium
plate sets by connecting one test lead to N4 and the other to F6 (diode 3), then to C6
(diode 4). Both should beep or not beep. Reverse test leads and repeat connections.
The beep should be opposite (both should not beep or beep). Repeat the test using P4
instead of N4 to test diodes/selenium plate sets (diodes 1 and 2).
An ohms scale
may be used.
A good diode has very high resistance
direction and low resistance in the other direction.
With power OFF, check for loose connections from F6 to F7, C6 to C7, P1 to
P2, P2 to P4, and N1 through N4, and continuity of all wires between those points.
Repair or replace loose connections and replace damaged or broken wires, if possible.
If no problems are found, replace the stacks.
Anode Bed. Before a great deal of time is expended troubleshooting an
anode bed, it should be determined from records if there is sufficient anode material to
attempt locating and repairing the fault. Generally, if the current and time is calculated
to amp years, comparing that number to the weight of the installed anodes and the
weight loss of the anode material will indicate if the anodes are expended or have
significant life remaining. Another indicator is if a gradual failure occurred over a period
of time, the anodes have failed. If the failure was sudden, a cable break can be
expected. If failed anodes are found, replace the anode bed. If a broken anode lead is
found, repair the cable. The first step to locating the break is to find the location of any
excavations that have occurred in the area of the anode cable. There are two methods
of troubleshooting anode beds, depending upon whether all anodes have failed (no
current), or some (or most) of the anodes have failed. If one or more anodes are
functioning, see paragraph 5-2.8.1. If no anodes are functioning, see paragraph 5-
If one or more anodes are functioning, the best method is first to locate the
functioning anodes, then an anode bed gradient graph to isolate and locate the
Note: If separate anode lead wires in a junction box were installed, use these to
measure the anode current and determine the functioning anodes.
Perform a close interval survey over the anode bed. For the purpose of
troubleshooting, you may adjust the rectifier to the highest voltage setting that would not
result in coating damage to the structure, to allow easier location of the anodes.
Measure the potentials over the anodes with a handheld multimeter on the DC volts
scale. With power ON, connect the positive lead of the multimeter to the structure lead
(N4) of the rectifier. Using a copper/copper sulfate reference cell connected to the