Which statement is true about the auxiliary current in the described test setup?

• A. The auxiliary current is placed next to the potential probe
• B. The auxiliary current is placed 30.5 m away
• C. The test uses a four-terminal method
• D. The test measures conductor insulation

Answer: (B)

The main idea here is why the current path is kept a specific distance from the sensing point to avoid skewing the voltage measurement. In this test setup, the potential probe is meant to read the voltage drop along a defined path without being perturbed by the local current injection. Placing the auxiliary current source 30.5 meters away creates separation that minimizes interference from the current-carrying electrodes and their contact resistances, yielding a more stable, repeatable measurement. That spacing is a deliberate, standard condition, which is why the statement about the auxiliary current being placed 30.5 meters away is the correct description.

Keeping the current source right next to the potential probe would distort the reading due to strong local fields and contact effects, which is why that option isn’t correct for describing the setup. The existence of a four-terminal arrangement or the goal of measuring insulation aren’t the focus for this specific detail about current-path placement.