UFC 3-570-06
JANUARY 31 2003
Figure 7-21. Testing for a Short Between Two Structures with Power Supply
V oltm et er
T em po ra ry
T est Po in t
+ -
T est Po in t
Po w er
2
T em po ra ry Su pp ly
1
A no des
R eference
+ -
E lect rod e
Ov er 5 0 Feet
S tru c tu re W ith o u t C P
S tru c tu re W ith C P
7-9.2
Testing for a Short Between Two Structures with Cathodic Protection
on Both Structures. Take a potential measurement of both structures by changing
only the structure connection without moving the copper/copper sulfate reference
electrode.
7-9.2.1
If the two potential measurements are significantly different (over 25 mV), the
two structures are not metallically shorted together. Under normal conditions, both
structures should have a potential more negative than -0.85 volts DC.
7-9.2.2
If the two potential measurements are not significantly different (under 25
mV), the two structures may be shorted and additional testing is required.
If one or both of the protected structures have impressed current systems,
turn off the rectifier on one system. Repeat the potential measurement of
both structures. If the potential of the structure with the rectifier still on
remains approximately the same or changes in a negative direction when
the potential of the structure with the rectifier off changes in a positive
direction (less negative), they are not shorted. If both potential
measurements change more positive approximately the same magnitude
when one system's current is interrupted, the two structures are shorted
together.
7-33
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