IR Drop — ON vs Instant-OFF (Diagram #004)

Shows how ON potentials include IR drop and how instant-OFF approximates polarized potential by removing IR drop (soil voltage gradient).

What this visual explains

This diagram distinguishes ON potential (includes IR drop from soil voltage gradients) from instant-OFF potential (removes most IR drop). The difference between ON and OFF is the IR component, not “extra polarization.”

Diagram

IR drop concept showing ON potential versus instant-OFF potential and the IR component between them. — Diagram #004 — ON includes IR drop; instant-OFF removes most IR drop.

How to read it

E_ON: structure-to-soil reading while CP current is applied (includes IR drop).
E_OFF: instant-off reading captured immediately after interruption (minimizes IR).
IR drop: voltage component caused by current through soil resistance (ΔV between ON and OFF).

Field interpretation

Large ON–OFF separation often indicates significant soil voltage gradient near the test location.
Instant-off is used when you need a closer estimate of polarized potential for criteria evaluation.
Proper interruption timing and synchronized interrupters matter for meaningful OFF values.

Common mistakes

Using ON values to claim compliance when IR drop is large.
Capturing OFF too late (not “instant”), allowing depolarization to begin.
Assuming OFF is “true potential” in every scenario (stray currents and dynamic conditions can still distort it).

CP 3 relevance

IR drop and instant-off interpretation are core CP 3 field concepts. Many troubleshooting questions depend on knowing what part of the voltage is polarization vs what part is IR.

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