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Q.If a copper water pipe is in contact with the metal sheathing of BX cable, can that contact cause the cable to corrode?

A.Corresponding editor Paul Fisette responds: Yes. The flexible sheathing on BX or AC (armored cable) is made of aluminum or galvanized steel, and contact with a copper water pipe can cause it to corrode over time.

Galvanic corrosion occurs when dissimilar metals are placed close together in the presence of an electrolyte like water. In this case, condensation on the pipe functions as the electrolyte. The zinc coating or aluminum (anode) is sacrificed to the copper (cathode), which remains intact.

There is perhaps a more important concern than corrosion: Such contact can be dangerous. The metal sheathing on the cable functions as the exclusive grounding path for the wire. In case of a short or ground fault, a pipe touching the cable could be charged and become a hazard.