Goals and Symptoms

Communications to a Micrologic Trip unit can not be established.
The Micrologic Type A, P, or H Trip units are configured as 4- wire slave devices connected to a CNV100 (2 to 4 wire RS485 converter).
The 2 wire side of the CNV100 is connected to a ION Meter that has been gatewayed.
All communications settings have been verified on all devices connected.
The wiring was pre-wired in OEM electrical EQUIPMENT.

Causes and Fixes

A common issue has been seen in OEM Switchgear communication wiring. The 4-wire side of the RS485 converter (CNV100) may have the transmit of the Micrologic Trip unit connected to the transmit of the CNV100 and the receive connected to the receive. Proper wiring would be for the master device (CNV100 4- wire side) to have the transmit wires connected to the receive on the Micrologic Trip Unit , and the receive wires connected to transmit on the Micrologic Trip Unit. The correct wiring diagram of the CNV100 is shown below. In this configuration the 2-wire side of the CNV100 is a slave and the 4-wire side is a master. The Green and White wires represent the receive, the Red and Black wires represent the transmit of the Micrologic Trip Units.
The same connections can apply for any 4 wire RS485 device.