CONVENTIONAL: A pole mounted transformer with two primary bushings is sometimes referred to as "conventional". It can be used individually to provide single-phase power or it can be banked with two like transformers to provide three-phase power.
CSP: Pole mounted transformers with one primary bushing are utility type transformers and are the type most commonly used in residential applications. The primary bushing is labeled "H1" and a grounding nut on the tank is labeled "H2". This transformer is connected between a phase and neutral. Some of these transformers are CSP (completely self protected). They usually include a primary fuse, a primary arrester, and a secondary breaker with weak-link.