The eSP is a special application version of our outdoor mounted slip-over BCT, developed specifically for the SP/SPS power circuit breaker. This circuit breaker is one of the most popular in its class up to 72kV and has been in existence since 1980 when it was first manufactured. We are offering this self contained model as a solution to add additional Current Transformers (CTs) when originally supplied with only one per pole, to change out older CTs for system upgrades or to replace aged and failing CTs when retiring the breaker is not an option.


The toroidal core is continuously tape wound using cold rolled grain oriented electrical grade silicon steel, which receives a full stress relief anneal after it is wound to its specified dimensions. The secondary winding is then wound of insulated copper magnet wire over the insulated core with the turns equally spaced around the core periphery. When taps are pulled, they are wound in a manner that assures a fully distributed winding between any connections. The coil is then fully encapsulated in an ANSI 70 (sky grey) resin system that has been developed and tested for outdoor use. The potting compound is U.V. stabilized, is flexible to allow for expansions caused by temperature variations from -50°C to +65°C, has good chemical resistance, high dielectric strength, rugged physical properties to endure mechanical shock, and overall excellent weather resistance. The eSP is cast with aluminum mounting hubs which are used to transfer the mounting forces away from the potting compound, and are fixed to align with the existing bolt pattern.


The primary polarity H1/P1 is identified on its surface by an embossed colored dot. The secondary terminals are ¼-20 silicone bronze studs provided with hex nuts and cupped washers. Terminal identification is permanently embossed with dual designations “X” and “S” for compatibility in the global market. The X1/S1 terminal represents the instantaneous polarity reference with respect to H1/P1 and is identified by an embossed colored dot. A cast aluminum conduit box with (2) 1” NPT hubs and blanking plugs is provided with a removable cover.


An aluminum nameplate with all required information and ratings, along with serial number and connection diagram, is affixed to each unit.

Outdoor Mounted Slip-Over BCT Specific Mounting Application


The eSP is custom designed to fit over the existing bushing (without removal) directly onto the interrupter frame, or onto an existing CT if present. Due to the angle at which the bushings are oriented, the CTs must be carefully lowered to avoid any damage. Typically, due to the height restriction, only 2 CTs can be mounted per pole. If replacing existing CTs, usually the same hardware can be used. If the new stack height exceeds the existing stack, or if adding an additional CT over an existing CT, then a hardware kit will be required. In some instances a 3rd CT may be installed provided the stack height does not exceed the bushing flange height. The top most CT of the stack shall be covered with a custom fitted ground shield.

Handling and Storage:

For domestic shipments the eSP is usually palletized with spacers between units and the pallet to allow for lifting. Ideally they should be lifted using endless slings in a 2-point or 3-point arrangement, lifting by fork lift or overhead hoist, one unit at a time. Caution should be employed while moving to avoid damaging or chipping the insulation and any sudden impacts to the unit or the conduit box. The units are outdoor rated so they may be left outside as originally packaged, but preferably should be stored indoors until ready for use. Pallets should not be stacked.

Size Selection:

The eSP has been designed for a specific mounting arrangement. A standard selection of ratio and accuracy class is shown in the table on the reverse side of this bulletin, with a limited cross-reference to existing Siemens CT part numbers. The list is not complete, nor is it limited to only those shown.


  • Other ratios and accuracies available
  • Can be designed to IEC and CSA standards
  • Can be designed for 50Hz power frequencies
  • Conduit box can be supplied with hub sizes up to 1.5” NPT
  • In some cases dual-core units may be possible