Replacement current transformers for SP/SPS/SPS2/SF6 | T.Replacement current transformers for SP / SPS / SPS2 / SF6 power circuit breakers 04/01/2013 - Volume IV - Issue I Current transformers (CTs) on the SP / SPS / SPS2 circuit breakers are enclosed in a die cast aluminum housing which has provided many years of trouble free protection for the active CT element which is encapsulated in resin.