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RepWars Briefing - Questions & Answers
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Question...
"I am an engineer involved in a Domestic Supply Improvement project for County Schools. The existing main is PVC located below grade and serves several buildings. Each building main is independently grounded to the electrical system at the point it enters the buildings. Thus, each building piping network (overhead copper) is grounded. However, I am designing a new overhead (above grade) copper main to tie each building together. What kind of problems may exist with electrolysis due to multiple grounds now interconnected by the main? Should I insulate the buildings from each other with a section of plastic pipe or some other means?
Your assistance is greatly appreciated.
"
RepWars Reply...
The grounding cable for each building is sized based upon the building's electrical service per the NEC. You should consult with an electrical engineer
and verify if connecting the copper water piping to the other buildings jeopardizes the grounding systems or violates the intention of the NEC.
To be safe, or to save design time, you may consider isolating the piping systems from one another as you suggested. A short section of Schedule 40
PVC would be sufficient (cold water only). If you do this, specify that the copper adaptors be at ambient temperature during connection to the PVC and
that heat generated from soldering not be transmitted to the PVC piping. Supports should be provided on the copper piping adjacent to each
PVC connection. You may consider using manufactured dielectric couplings, flanges or unions for isolation, however, many of these will still
allow external electrical continuity. Be sure to verify that they will completely isolate the piping systems before you specify them. Check with the
manufacturer.
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