The effectiveness of cathodic protection is evaluated by measuring the potential difference between the end of the cable connected to the buried structure and a reference electrode placed on the surface of the soil above the structre.
The potential values with switched on current (Eon potential) must be corrected taking into account the ohmic drop between the structure and the reference electrode. It is better to measure the potential just after the current has been switched off (Eoff potential).
(S) ) buried structure, (A) : anode, (P) : power, (Ref) : electrode , E : millivoltmeter.
The 100mV criterion can be applied with precautions like an alternative on the buried structures, as it is explained below.