This paper describes a new probe for potential monitoring of cathodically protected structures. Features of the probe are: elimination of copper sulfate solution, elimination of interliquid potential contribution, elimination of ohmic drop contribution, reliable measurement in presence of stray currents, and high durability. The probe is composed of a steel coupon and a reference electrode, both embedded in an alkaline mortar, simulating a coating defect. Different types of internal reference electrodes were tested, like Mixed Metal Oxide (MMO) titanium activated and AISI 304 stainless steel. The different probes were tested using different types of mortar; alkaline mortar (obtained from portland cement and sand), chloride containing mortar and carbonated mortar. Laboratory tests were carried out to verify the electrode durability under cathodic polarization and in presence of variable interfering electric field, simulating the presence of stray current. The results of two year laboratory test and a first field test are reported and discussed. The MMO reference electrode was more stable and more reliable than stainless
steel when strong electric fields were present. Alkaline probes seemed to be more stable than other mortar type.
Keywords: stray current, cathodic protection, potential measurement, ohmic drop, CP corrosion coupon.