Chris, can I use the same thread compound on both PVC-coated steel and PVC-coated aluminum?
No, because different material types require different thread compounds. According to NEC Article 300.6 A, “all field cut threads shall be coated with an approved electrically conductive, corrosion-resistant compound.” Most manufacturers of PVC Coated Conduit will offer an approved conductive thread compound in their catalog for galvanized rigid conduit. However, when applying thread compound to aluminum, a lithium-based compound such as STL8 or Noalox should be used instead. This is because other compounds can contain copper which can cause damage to aluminum threads. Using the correct thread compound for the correct material type can help maintain grounding continuity and prevent galling of threads.