CHAPTER 3: INSTALLATION WIRINGD30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 3-253Figure 3-21: Contact input and output module wiring (Sheet 3 of 3)3.3.6.1 Contact inputsA dry contact has one side connected to terminal B3b. This is the positive 48 V DC voltage rail supplied by the power supplymodule. The other side of the dry contact is connected to the required contact input terminal. Each contact input grouphas its own common (negative) terminal that 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 thiscontact is connected to the required contact input terminal. If a wet contact is used, then the negative side of the externalsource must be connected to the relay common (negative) terminal of each contact group. The maximum external sourcevoltage for 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 3-22: Dry and wet contact input connectionsFor proper functionality, observe the polarity shown in the figures for all contact input and outputconnections.Where a tilde “~” symbol appears, substitute the slot position of the module.
