Article 0074 — It is a condition, not a number of feet. You find it with a voltmeter, it moves with the current crossing the pipe, and the place it hides is the one place you most need it.
DC Interference vs. DC Influence: Know the Difference Before You Bond
Article 0071 A foreign CP system can shift your readings without exchanging any current with your pipe. Interference damages steel; influence damages data. Test before you bond.
Article 0065 When the voltmeter reads protection but the steel is still corroding — and how the composite reading hides what's actually happening at the pipe.