3-14 L30 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUALWIRING CHAPTER 3: INSTALLATION3An LED on the front of the control power module shows the status of the power supply, as outlined in the table.Table 3-2: Power supply LED on front panelFigure 3-13: Control power connection3.3.4 CT/VT modulesThe CT and VT inputs are analog current transformer and voltage transformer signals used to monitor AC power lines. TheUR-series relays support 1 A and 5 A CTs.A CT/VT module can have current or voltage inputs on channels 1 through 4 inclusive, or channels 5 through 8 inclusive.Channels 1 and 5 are intended for connection to phase A, and are labelled as such in the relay. Likewise, channels 2 and 6are intended for connection to phase B, and channels 3 and 7 are intended for connection to phase C.Channels 4 and 8 are intended for connection to a single-phase source. For voltage inputs, these channels are labelled asauxiliary voltage (VX). For current inputs, these channels are intended for connection to a CT between system neutral andground, and are labelled as ground current (IG).To connect 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.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.LED indication Power supplyContinuous on OKOn/off cycling FailureOff Failure or no powerVerify 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.
