Connection to the Modbus-SL Network with BSCM Modbus SL/ULP Module and Modbus SL Hub

Introduction

Connect ComPacT NSX or PowerPacT H-, J-, and L-Frame intelligent modular units to the Modbus network with the Modbus SL hub and the BSCM Modbus SL/ULP module.

The 24 Vdc power supply terminal block delivered with the Modbus SL hub is used to supply the Modbus SL hub with power either in a daisy-chain or in a star connection.

A maximum of 12 circuit breakers (or IMUs) can be connected to stacked modules (IFE server, IFM interface, or Modbus SL hub).

Example of a maximum configuration with 12 circuit breakers:

• 1 IFE server connected to 1 circuit breaker.

• Stacked to 1 IFM interface connected to 1 circuit breaker.

• Stacked to 4 Modbus SL hubs, connected to a maximum of 10 circuit breakers. 2 RJ45 ports remain free on the Modbus SL hubs.

In terms of Modbus communication, it depends on the performance requirement. As it takes approximately 500 ms at 19,200 Baud per device to refresh 100 registers, the more interfaces added the longer the minimum refreshment period. The minimum refreshment period depends on the number of Modbus SL hubs stacked to one IFE server or connected to Panel Server gateway. Multiply the time to refresh one device by the number of devices to find the minimum refreshment period expected in the application. For instance, an installation with eight BSCM Modbus SL/ULP modules or IFM interfaces connected to one gateway at 19,200 Baud would take approximately 4 seconds to be read.

Connection of the BSCM Modbus SL/ULP Module to the Modbus SL Hub

Up to three BSCM Modbus SL/ULP modules can be connected to one Modbus SL hub by using a BSCM Modbus SL cord.

Three BSCM Modbus SL cords are available:

• BSCM Modbus SL cord with commercial reference LV434221 (0.35 m / 1.15 ft)

• BSCM Modbus SL cord with commercial reference LV434222 (1.3 m / 4.26 ft)

• BSCM Modbus SL cord with commercial reference LV434223 (3 m / 9.84 ft)

The BSCM Modbus SL/ULP modules are powered by the Modbus SL hub.

A	Modbus SL hub
B	ComPacT NSX / PowerPacT H-, J-, and L-frame circuit breaker
C	BSCM Modbus SL/ULP module
D	Modbus SL cord

Daisy Chaining of a Modbus SL Hub with an IFM Interface

It is possible to chain the Modbus-SL network by using an RJ45/RJ45 plug-plug cable between:

• One of the three RJ45 ports of the Modbus SL hub

• The RJ45 Modbus SL port of the IFM interface

Three Modbus SL cables are available for this connection:

• Modbus SL cable with commercial reference VW3A8306R03 (0.3 m / 0.98 ft)

• Modbus SL cable with commercial reference VW3A8306R10 (1 m / 3.28 ft)

• Modbus SL cable with commercial reference VW3A8306R30 (3 m / 9.84 ft)

The 24 Vdc power supply is not distributed through the Modbus SL cable.

Daisy Chaining of a Modbus SL Hub with Modbus SL Devices

The Modbus SL hub can be connected to another Modbus SL device that does not have a Modbus RJ45 port (for example, a Panel Server gateway) by using a Modbus SL cable connected on the Modbus SL hub terminal block.

The 24 Vdc power supply can be chained or not through the Modbus SL cable.

Modbus SL Hub Terminal Block

The Modbus SL hub terminal block is used to connect the Modbus SL hub to another Modbus SL device.

Illustration	Marking	Description
	24V	24 Vdc power supply
	0V	0 V for Modbus common and power supply
		Ground terminal
	D0	RS 485 A/A’ or Rx-/Tx- signal
	D1	RS 485 B/B’ or Rx+/Tx+ signal

Composition of the Modbus Cable

A	Outer sheath
B	Shielding braid
C	Twisted pair sheath
D	Communication pair (white/blue)
E	Power supply pair (red/black)

The characteristics of the Modbus cable are as follows:

• Shielded cable with two twisted pairs:

  • One pair with 0.14 mm² (24 AWG) cross section for the RS 485 signal (D0, D1).

  • One pair with 0.14 mm² (24 AWG) cross section for the 24 Vdc power supply (optional, only used if the Modbus SL hub is not powered through stacking by another device).

• Shielding braid to be connected to the ground terminal of the Modbus SL hub terminal block.

The 0 V terminal of the power supply pair is also the Modbus common, that is the 0 V for the RS 485 signal (D0, D1).

IMPORTANT: The 0 VL cable (Modbus common) must be distributed along the entire length of the network, right up to the Modbus client.

Modbus Line Termination on the Modbus SL Hub

• Plug the Modbus line termination with commercial reference VW3A8306RC in one of the three RJ45 Modbus SL ports of the Modbus SL hub.

• Connect the Modbus line termination with commercial reference VW3A8306DRC to the Modbus SL hub terminal block.