DC Interference Testing
Purpose
Determine whether a suspected DC source influences an affected structure, characterize likely pickup/discharge behavior, identify current/path evidence, and collect sufficient evidence for mitigation and verification.
1. Define the test system
Define the suspected source(s), affected structure(s), interfering system(s), electrical connections, bonds, isolation, and test boundaries.
2. Declare directional conventions
Declare meter/shunt polarity and the positive-current direction for every directional current measurement. An unsigned current magnitude cannot establish pickup or discharge direction.
3. Establish baseline conditions
Establish baseline structure-to-electrolyte potentials and relevant source operating states using the governing measurement resources.
4. Correlate with controlled source switching
Where a controllable source exists, correlate affected/interfering structure response with controlled source switching. Record which sources were switched and which remained active. Source-correlated response establishes influence under the controlled conditions; it does not by itself prove damaging discharge.
5. Collect current/path evidence
Measure or log relevant evidence as applicable: longitudinal structure current and direction, bond current, current mapping, and/or earth/side-drain gradient evidence.
6. Treat dynamic sources as dynamic
For dynamic sources, use synchronized/time-correlated logging of adequate duration. Do not substitute one spot observation.
7. Map spatial response
Look for coherent source/path/pickup/transport/discharge evidence rather than relying on one potential shift.
8. Evaluate severity within the controlled framework
Use the controlling multifactor framework and applicable asset-specific CP criteria. Do not invent a universal mV, A, A/m², or bond-current limit.
9. Select mitigation only after the current-path model is supported
Do not treat a bond or any other mitigation as automatically correct. Mitigation changes the electrical network and can move the problem.
10. Verify after mitigation
Repeat the relevant measurements after mitigation and verify consequences to both systems and other relevant nearby structures.
11. Record limitations
Record uncontrolled sources, inaccessible test points, uncertain current direction, mixed potentials, timing limitations, and other conditions that constrain interpretation.