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INTRODUCTION

CMeX20 is a DIN-mounted External MCM that converts IR to M-Bus. It 
enables standard M-Bus communication for all CMeX Series products 
and DIN-mounted ABB electricity meters using IR interface. For a 
complete description of the product or for information in Swedish, visit 
the Elvaco AB website, www.elvaco.com.

OVERVIEW

CMeX20

External MCM for ABB B21/B23/B24, M-Bus

1. 

Serial number 
(secondary address)

2. 

LED

3. 

M-Bus connector

4. 

M-Bus in

5. 

M-Bus in

6. 

M-Bus out

7. 

M-Bus out

MOUNTING

The CMeX20 is mounted on a DIN-rail. The metallic clip on the bottom 
is used to mount and demount the unit from the DIN-rail. Mount the 
CMeX20 on the left side of an ABB electricity meter or another CMeX 
Series product.

M-BUS 2-WIRE BUS

M-Bus is a multi-drop 2-wire bus with no polarity. Use a cable of area 
0.25-1.5 mm

2

, e.g. a standard telephone cable (EKKX 2x2x0.5). Connect 

the M-Bus 2-wire to the screw terminals (4) and (5) or pin terminal (3).

IMPORTANT 

• 

All connected M-Bus slave devices must have unique M-Bus 
secondary or primary addresses depending on addressing mode.

• 

Measure voltage over M-Bus slave connection to verify M-Bus 
master connection. Voltage should be between 21-42 VDC.

LED INDICATIONS

The product is equipped with a single orange LED, which shows 
communication status.

Orange LED

 

Mode

Product state

Visual

Permanently on

M-Bus connected

Flashing

M-Bus communication

TROUBLESHOOTING

Product does not respond to M-Bus master commands  
Please verify your M-Bus slave configuration and connection:

• 

Voltage over M-Bus connection should be between 21 VDC and 42 
VDC.

• 

All M-Bus slaves connected to the M-Bus master must have 
unique primary addresses or secondary addresses depending on 
addressing mode.

• 

Verify M-Bus slave baud rate used by M-Bus master. M-Bus master 
baud rate must be identical to M-Bus slave baud rate.

SAFETY

The warranty does not cover damage to the product caused by usage in 
any other way than described in this manual. Elvaco AB can not be liable 
for personal injury or property damage caused by usage in any other way 
than described in this manual.

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