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Can a Micrologic trip unit communicate with 2 wire communications wiring?

Published date: 19 June 2019

Product Line
Masterpact (NT and NW) and larger frame size Powerpact (P and R Frame) and Compact NS Circuit Breakers

Trip Unit Trip Function Type
2.0A (IEC Only) LSO Standard
3.0A LI
5.0A LSI
5.0P LSI Power
5.0H LSI Harmonics

Communication applications using Micrologic trip units in 2 wire configurations

Older version of the breaker communication module (BCM) are not capable of 2 wire communication. The replacement, BCM ULP version, is capable of 2 wire communication
The Micrologic trip unit must have a breaker communications module (BCM) with gray terminals. If the device has green terminals on the BCM, it is not capable of the 2 wire communications configuration, 4 wire only. Below the figures show the two units.

There are three possible wiring configuration for a BCM ULP, 4 Wire, 2 Wire, and 2 Wire + ULP. See the figure below for the wiring diagram for each configuration. As you see from the diagrams, the 4 wire and 2 wire configurations have the same setting on the trip unit, 4 Wire. The BCM can auto detect the correct setting.  The 2 Wire + ULP setting provides two terminals for 2-wire Modbus communication and 2 terminals for ULP protocol. ULP is a protocol common to many Schneider devices including Micrologic trip units and FDM121 display is diagram.

The 2 Wire + ULP is the default setting on the BCM ULP. The configuration can be set using a Micrologic RSU, see the link below. The Micrologic A trip unit must be set using this program.  P and H type trip units can be configured from the front panel using the procedure below. See the instruction bulletins for more information.

  1. Press the Wrench button
  2. Select the Com. Setup
  3. Select Communication Parameter
  4. Select 4 wire or 2W + ULP

Powerpact P, R, and Masterpact NW, NT Micrologic™ 5.0P and 6.0P Trip Units, see 48049-137-05
Powerpact P, R, and Masterpact NW, NT Micrologic™ 5.0H and 6.0H Trip Units, see 48049-330-03

Link to Micrologic RSU program.


  • Powerpact H, J, and L and Compact NSX breaker use different communication hardware (IFM, NSX cord, and BSCM). The breakers use 2 wire configuration only.
  • If the BCM date code is 11351 to 12132, the user may see ComLoss errors in SMS. The user must either be running SMS 4.3 with the Micrologic patch or replace the BCM with date code 12132 or higher.
  • The Micrologic trip unit must be type P or H with date code 11351 or higher.
  • If a Cradle Communication Module (CCM) is use, it must have the new firmware to operate with 2 wire + ULP.  The CCM with the new firmware is Brand Schneider Electric and the CCM with the old firmware is brand Merlin Gerin.

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