Where should a dielectric union be installed in propane piping?

• A. Between regulator and outdoor piping
• B. Between riser and indoor piping
• C. At the tank outlet
• D. At the service entrance

Answer: (B)

Dielectric unions prevent galvanic corrosion by electrically isolating two different metals in a propane piping system. They are placed where outdoor piping made of one metal meets indoor piping made of another, so the metals don’t form a continuous electrical path through the gas line. The junction between the outdoor riser (usually steel) and the indoor piping (often copper) is exactly where this isolation is needed. Using a dielectric union there stops electrolysis at the point where the metals join, helping protect the piping from corrosion and leaks. Placing it at other points (such as between the regulator and outdoor piping, at the tank outlet, or at the service entrance) doesn’t address the typical dissimilar-metal interface and isn’t how this protection is applied.