In order to monitor in-time the occurrence of localized corrosion in concrete structures (viaduct, aqueduct, PCCP, pre-stressed and post-tensioned structures), a multi-reference electrode was proposed and studied, consisting of a series of continuous metallic wires able to measure the potential of carbon steel rebars and tendons. Because chloride-induced pitting may provoke hydrogen embrittlement of high strength steel, an early detection of corrosion initiation is very important to avoid such brittle fracture. Laboratory tests on mortar samples simulating post-tensioned tendons corrosion, induced by chlorides, confirmed the effectiveness of this new reference electrode. For its application to PCCP, a FEM analysis was performed to determine the optimal electrode size as a function of pipe diameter, concrete cover and soil resistivity. Results are reported and discussed.