3-22 M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUALWIRING CHAPTER 3: INSTALLATION33.3.6.1 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 3-19: Dry and wet contact input connectionsThere is no provision in the relay to detect a DC ground fault on 48 V DC control power external output. We recommendusing an external DC supply.3.3.6.2 General application considerationsContacts outputs of protective relays, auxiliary contacts from breakers, disconnectors and other devices, are generallyconnected to contacts inputs of protective relays. In some situations, the contact outputs of some protective relays canhave high impedance connected across it. When such a contact output is connected across a M60 contact input, it canspuriously operate the M60 input even when the output is open, if there is a substantial distributed capacitance(represented by C1) present in the wiring between the output and the M60 input and the debounce time setting in the M60relay is low enough. This false assertion of the contact input, when there is inadvertent ground present at the DC positiveterminal, can be prevented by inserting a resistor across the M60 input.The following figure shows a typical DC circuit, with battery ground detection, of contact input. The contact output hasparallel impedance across it (represented by R1).Where a tilde “~” symbol appears, substitute the slot position of the module.
