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Stray Current Interference 6:6
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
02/01/05
Stray Current Corrosion Control
There are several ways to control stray current. Sometimes it is possible to
relocate or remove the source of the current. Proposed structures might be
rerouted to avoid a source. Among the most common methods are the
installation of mitigation bonds and the use of cathodic protection.
Mitigation Bonds
Mitigation bonds , also called drain bonds or cables, provide a metallic path
between the affected structure and the source of stray current. This permits
the current to be drained through the cable back to the source rather than
leaving the structure through an earth path.
A resistor may be incorporated in a bond to control the amount of stray
current being drained. If dynamic currents are involved, a diode or reverse
current switch may be needed to prevent reversal of current flow.
Mitigation bonds need to be maintained. If not kept in good working order,
the affected structure may undergo serious corrosion. An important part of
your work is to make regular inspections, which are required in various
regulated industries, to insure that the bond is operative and is draining the
proper amount of current.
Figure 6.3 shows the use of a mitigation bond to solve a stray current
problem stemming from a rail transit system. Figure 6.4 illustrates a similar
bond for mitigating cathodic interference.