Table 54. Comparison of galvanic and impressed current 

 protection systems. 



Galvanic 



Impressed Current 



No external power 

 required 



External power 

 source required 



Relatively low installa- 

 tion and maintenance costs 



Higher installation 

 and maintenance 

 costs 



Frequently requires no 

 additional right of way 



Applied voltage and 

 current may easily 

 be varied 



Adjusts current output as 

 structure potential varies 

 (especially zinc anodes) 



Protects larger and more 

 extensive structures 



Severely limited current 

 output 



Suitable for high 

 resistivity electrolytes 



Useful primarily in low 

 resistivity electrolytes 



Monthly power bill 



Interference with foreign 

 structures usually non- 

 existent. 



Can cause interference 

 problems with foreign 

 structures. j 



immersed anode leads and header cables. Insulation should be 600-volt type 

 and be suitable for direct burial service. High molecular weight, high 

 density polyethylene has a good record for satisfactory use. Insulation 

 quality of all subsurface electrical connections is equally important for 

 the same reasons. Satisfactory electrical connection methods for copper 

 wire include soft soldering, powder welding (such as Cadweld) , silver 

 soldering, phoscopper brazing, crimp-type couplings, and split-bolt couplings, 

 The first four, if done properly, will provide metallurgical joining and 

 will be permanently of low resistance. Mechanical methods such as the last 

 two mentioned, again if done properly, will be satisfactory also. Joint 

 insulation should be of such quality as to at least equal the electrical 

 insulating qualities of the wire insualtion. Acceptable insulation methods 

 include cast epoxy as well as various tapes. There are several manufacturers 

 of cast joint insulation. Details of joining and insulating may be obtained 

 from cathodic protection material supply house catalogs. In all cases, 

 satisfactory performance life depends on the proficiency of the people 

 doing the work. Careful inspection of all phases of impressed current 

 anode installation is mandatory. 



b. Criteria for Cathodic Protection . Earlier it was stated that if 

 electric current is caused to flow from an external source through a common 



352 



