Troubleshooting 9:12
CP 1 – Cathodic Protection Tester Course Manual
© NACE International, 2000
07/01/04
Zero Current Output with Unchanged Voltage Output
If the DC voltage output of the rectifier is relatively unchanged but the
current output is zero, an open output circuit is indicated. This could be
caused by:
• Open fuse in the output circuit
• An open positive or negative lead wire
• A failed groundbed.
If an open fuse in the output circuit is found, a short exists (or has existed)
in the output circuit.
Significant Current Change with Unchanged Voltage
If the DC current output significantly changes with no change in the output
voltage, the output circuit resistance has changed. If the current output has
significantly increased, a lower circuit resistance is indicated. This could be
due to system additions, shorts to other underground structures, or major
coating damage. If the current output significantly decreased, a higher
circuit resistance is indicated. Some of the possible causes might include
installation of inline isolators, groundbed deterioration, discontinuity due to
disconnection of system component, or gas blockage. Seasonal variations in
soil conditions, such as drying or frost, can also increase the current
resistance.
Significant Changes in Both Voltage and Current Outputs
Sometimes both the voltage and current outputs will decrease significantly.
If the voltage and current outputs are approximately one-half of the normal
values, the most probable cause is partial failure of the rectifier stacks
(”half waving”). If the rectifier stacks are found to be operating properly,
the transformer should be investigated for possible winding-to-winding
shorts.
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