JANUARY 31 2003
interference currents and the possibility of surges or fault currents. If failure of the resistor
would result in loss of adequate protection to a structure that requires cathodic protection,
the resistance bond would be considered a "critical bond." Critical bonds must be tested
on a recurring schedule of not less than 60 days (paragraph 4-9.1).
of buried structures, both for the prevention of interference and for the proper operation of
cathodic protection systems.
Installing a Sacrificial Anode. In some cases, interference is controlled by
installing a sacrificial anode or anode bed on the foreign structure to raise the potential of
the foreign structure and provide a lower resistance path for discharge current to flow from
the installed anodes instead of the foreign structure. The use of a sacrificial anode to
control interference is shown in Figure 5-6. This method normally works well when the
interference current is fairly low and the foreign structure has a relatively good coating.
This method may be combined with coating the cathode (protected structure) near the
discharge area to lower the interference current.
Figure 5-4. Correction of Interference by Resistive Bonding
Measure Protected Structure
Measure Foreign Structure
Measure Anode Current Here
(by mV potential drop)
Protected Structure Leads
Foreign Structure Leads