Loc: Bucks County PA
Our utility (PECO) requires a 5th jaw to meter an existing 120 volt service, and also to meter a single phase 208/120 service supplied from a 3 phase system. Although I don't know how it functions, according to our utility co. drawings, it provides a neutral connection to the meter. Your utility company should have an installation guide book which will include drawings. Maybe someone else here can explain the function.
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