Cathodic Protection Tester Practice Exam

If a structure to electrolyte potential of -.850 Volts is measured, what is the equivalent conversion to Zinc?

1. -266 mV

2. +266 mV

3. 0.850 V

4. 0.266 V

The correct answer is: +266 mV

To understand the conversion of the structure to electrolyte potential of -0.850 Volts to a comparable value for zinc, it’s essential to consider the potential of the reference electrode used in cathodic protection systems. When we measure a potential relative to a reference electrode, we often convert that value to another reference material—in this case, zinc. Zinc has a more positive potential in comparison to many common reference electrodes, such as copper/copper sulfate. In the context of cathodic protection, the potential to a certain standard electrode, like zinc, is often expressed in millivolts (mV) for easier interpretation. Thus, converting -0.850 Volts to millivolts gives us -850 mV. To find the equivalent value for zinc, we take into account the electrochemical series and the standard reference potential of zinc, which is approximately -0.976 volts relative to a saturated copper/copper sulfate electrode. This calculation indicates that if the measured potential at the structure is -0.850 V, and we know this is more noble than zinc, we subtract the potentials: -0.850 V (which is equivalent to -850 mV) minus -0.976 V (which is the