Connections from the three-phase primary circuits (beneath the multipart-insulator transmission lines) to two underground risers (aka, a metal or lead pipe containing the three cables) was accomplished by an "interface" on the pole whereby the conductors from the overhead and underground joined together. This was accomplished within the two, three-fingered pieces of equipment on the pole, commonly known as a "potheads". The terminating ends of the overhead and underground cables were connected within it, sealed and bathed with heat-absorbing oil to keep the high-voltage joints running cool and lots of heavy tape around their porcelain bushings to further aid in keeping water out.