Burndy Penetrox E consists of a non-petroleum base vehicle in which copper granules are suspended. Recommended for copper to copper applications, grounding and for use on copper conduit threads. UL Listed. When stored in its original container in cool (under 100 degrees F) dry environment, Penetrox oxide inhibiting compound will remain workable and functional for 5 years from the date marked on the container provided it is mixed per instructions prior to use.