Electrolosys can occur anytine two dissimilar metals are in contact with one on another, however the reaction is not nearly as rapid in a dry contact as it is on the inner walls of a pipe with a constant flow of water. For tht reason, when running copper pipe it is essential to use copper or copper clad hangers instead of galvanized steel.
Both plumbers and HVAC duct installers are trained to avoid direct contact between the two systems, however that does not insure that it wont occassionally happen.
If you have copper in direct contact with galvanized steel you should try to reposition one or the other to avold the contact. If that is not possible the point of contact should be electrically insulated by applying common black electric tape to prevent contact between the two surfaces.
Also, check in the vincinity of your water meter to see if your water system is grounded? There should be a bare copper wire clamped to the pipe and running to the house electrical ground near the main electrical panel.
If your main water line coming into the house is a metal line (iron pipe or copper tubing) there should also be a copper wire clamped to the pipe on either side of the meter to insure a continuity of ground in the event the meter is pullled out for service.
Although it used to be a common practice due to recent changes in both the National Electrical code and the Plumbing codes, Electrical appliances and devices should not be grounded to the water pipes.
