3-18 D30 Line Distance Protection System GE Multilin3.2 WIRING 3 HARDWARE3CONTACT INPUTSA dry contact has one side connected to terminal B3b. This is the positive 48 V DC voltage rail supplied by the power sup-ply module. The other side of the dry contact is connected to the required contact input terminal. Each contact input grouphas its own common (negative) terminal which must be connected to the DC negative terminal (B3a) of the power supplymodule. When a dry contact closes, a current of 1 to 3 mA flows through the associated circuit.A wet contact has one side connected to the positive terminal of an external DC power supply. The other side of this contactis connected to the required contact input terminal. If a wet contact is used, then the negative side of the external sourcemust be connected to the relay common (negative) terminal of each contact group. The maximum external source voltagefor this arrangement is 300 V DC.The voltage threshold at which each group of four contact inputs detects a closed contact input is programmable as17 V DC for 24 V sources, 33 V DC for 48 V sources, 84 V DC for 110 to 125 V sources, and 166 V DC for 250 V sources.Figure 3–19: DRY AND WET CONTACT INPUT CONNECTIONSWherever a tilde “~” symbol appears, substitute with the slot position of the module.Contact outputs can be ordered as form-A or form-C. The form-A contacts can be connected for external circuit supervi-sion. These contacts are provided with voltage and current monitoring circuits used to detect the loss of DC voltage in thecircuit, and the presence of DC current flowing through the contacts when the form-A contact closes. If enabled, the currentmonitoring can be used as a seal-in signal to ensure that the form-A contact does not attempt to break the energized induc-tive coil circuit and weld the output contacts.There is no provision in the relay to detect a DC ground fault on 48 V DC control power external output. We recom-mend using an external DC supply.NOTENOTE
