CHAPTER 3: INSTALLATION WIRINGB30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL 3-173To connect to the module, size 12 American Wire Gauge (AWG) is used commonly; the maximum size is 10 AWG.CT/VT modules can be ordered with a standard ground current input that is the same as the phase current input. Each ACcurrent input has an isolating transformer and an automatic shorting mechanism that shorts the input when the module iswithdrawn from the chassis. There are no internal ground connections on the current inputs. Current transformers with 1to 50000 A primaries and 1 A or 5 A secondaries can be used.CT/VT modules with a sensitive ground input are also available. The ground CT input of the sensitive ground modules is 10times more sensitive than the ground CT input of standard CT/VT modules. However, the phase CT inputs and phase VTinputs are the same as those of regular CT/VT modules.These modules have enhanced diagnostics that can automatically detect CT/VT hardware failure and take the relay out ofservice.CT connections for both ABC and ACB phase rotations are identical, as shown in the Typical Wiring Diagram.The exact placement of a zero-sequence core balance CT to detect ground fault current is shown as follows. Twisted-paircabling on the zero-sequence CT is recommended.Figure 3-16: Zero-sequence core balance CT installationThe phase voltage channels are used for most metering and protection purposes. The auxiliary voltage channel is used asinput for the synchrocheck and volts-per-hertz features, which are optional features for some UR models.Verify that the connection made to the relay terminals for nominal current of 1 A or 5 A matches thesecondary rating of the connected CTs. Unmatched CTs can result in equipment damage orinadequate protection.Substitute the tilde “~” symbol with the slot position of the module in the following figure.
