UFC 3-570-06
JANUARY 31 2003
5-6.6
Installation of Nonmetallic Sections or Isolations. Installation of
nonmetallic sections or isolations on the foreign structure in the stray current pickup area
and between the pickup area and the discharge area may significantly reduce the amount
of interference current by substantially raising the resistance of the stray current path.
This type of action is usually adequate for metal fences. By isolating sections of fences
using two non-contacting fence posts, wooden fence posts or dielectric materials between
the fence hardware and the fence posts. Isolations can be made in the current pickup
area and between the pickup area and the discharge area, sometimes supplemented with
a sacrificial anode in the discharge area(s). This may be considered as part of a design for
an impressed current installation if there is a continuous metallic fence in the area where
an impressed current anode bed is to be installed or if a metallic fence is to be installed in
an area with an existing anode bed.
Figure 5-8. Use of Isolation on Foreign Structure to Control Interference
CP Power Source
Isolations or nonmetallic sections
CP Anode
Note: Install isolations or nonmetallic
sections in pickup area and between
pickup area and discharge area.
5-6.7
Application of a Small Impressed Current System. For interference
problems which are more serious, and where bonding or resistance bonding is not
possible or practical, consider the application of a small impressed current system on the
foreign structure in the discharge area to protect the foreign structure from stray current
corrosion. As shown in Figure 5-6, substituting a rectifier and impressed current anodes
for the sacrificial anodes, the corrosion is stopped by the application of sufficient cathodic
protection to the discharge area. Caution should be used to balance the two systems,
since this installation may interfere with the original protected structure that was causing
the stray current corrosion.
5-6.8
Combination of Techniques. In many cases, a combination of the preceding
mitigation techniques may be prudent. The magnitude of stray current, the soil resistivity,
the protected structure coating efficiency, the foreign structure coating efficiency, and the
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