CHAPTER 3: INSTALLATION WIRING
C70 CAPACITOR BANK PROTECTION AND CONTROL SYSTEM – INSTRUCTION MANUAL 3-17
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To 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 AC
current input has an isolating transformer and an automatic shorting mechanism that shorts the input when the module is
withdrawn from the chassis. There are no internal ground connections on the current inputs. Current transformers with 1
to 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 of
service.
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-pair
cabling on the zero-sequence CT is recommended.
Figure 3-16: Zero-sequence core balance CT installation
The phase voltage channels are used for most metering and protection purposes. The auxiliary voltage channel is used as
input 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 the
secondary rating of the connected CTs. Unmatched CTs can result in equipment damage or
inadequate protection.
Substitute the tilde “~” symbol with the slot position of the module in the following figure.
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