a mounting hole is drilled on the external wall of the cylinder body for receiving a reference electrode in contrast the cathodic protection system 11 illustrated in fig7 does not require any drilling since one of the remaining electrodes 31 may be used as a reference electrode with the plurality of anticorrosive electrodes 31 illustrated in fig7 the cathodic protection system 11 may employ any of the three power supply methods described above with reference to fig2 if the potential control method is selected a tester may be connected to one of the anticorrosive electrodes 31 as the reference electrode 12 and also connected to one of the other anticorrosive electrode 31 to measure the polarization potential fig8 is a block diagram illustrating another embodiment of an impressed current cathodic protection system 11 that includes redundant or plural electrodes 31 fig9 is a schematic cross section of the impressed current cathodic protection system 11 illustrated in fig8 the embodiment illustrated in fig8 through 10 includes a plurality of anticorrosive electrodes 31 protective current flows to each anticorrosive electrode 31 through the controller 18 fig1 is a circuit diagram of the controller 18 illustrated in fig9 as shown in fig1 the controller 18.