M-Bus Network Planning & Cabling Practice
Two-wire, polarity-free M-Bus wiring is forgiving on site — but segment sizing still needs a plan. Budget each segment by unit load, not by guesswork, and document every address before handover.
How to plan an M-Bus segment
Map devices and addressing
List every meter on the segment and assign primary addresses (1-250) or record secondary 8-digit IDs (manufacturer code, serial number, version, medium) for large or rotating installations.
Budget the unit-load capacity
Each slave draws a defined unit-load share from the master's power budget. Total the unit loads for the segment before adding devices — exact per-device and per-master figures come from the master's datasheet, not from a rule of thumb.
Add repeaters where the budget runs out
When a segment's unit-load total or cable run would exceed the master's rated capacity, split it with a repeater or level converter rather than pushing one long chain past its limit.
Draw the segment diagram and handover sheet
Record the segment layout, address list, and cable routing before commissioning — the building operator needs this to add or replace meters later without re-tracing the bus.
What matters in M-Bus wiring practice
Primary addressing range
Each M-Bus segment supports primary addresses 1 to 250 per device; secondary addressing (8-digit ID) is available where devices are pre-configured or swapped without re-addressing.
Polarity-free two-wire bus
The two-wire M-Bus line is polarity-independent — conductors can be connected either way round, cutting termination errors and rework on site.
Master powers the bus
The master supplies bus power (typically around 36V); meters answer by current modulation instead of generating their own signal voltage, which keeps the metering side simple and cheap.
Unit-load segment budgeting
Plan capacity by unit load per device rather than fixed distance alone — the same concept governs how many meters or how much cable a segment can carry before it needs a repeater.
Repeaters extend reach, not just length
Level converters and repeaters split a segment's load across sections, letting you add devices or cable run beyond what a single unbroken run supports.
wM-Bus as the cable-free variant
Wireless M-Bus (EN 13757-4) runs at 868 MHz in the EU with S, T and C modes — useful where cabling meters individually isn't practical, without abandoning the same application layer.
M-Bus network planning package
Segment design, address mapping, and handover documentation before you pull cable.
- Segment and unit-load capacity review against the master datasheet
- Primary/secondary address mapping per meter
- Repeater and level-converter placement where segments need splitting
- Segment wiring diagram for the as-built record
- Handover documentation sheet for the building operator
Frequently asked questions
Does M-Bus cable polarity matter?
No — the two-wire M-Bus bus is polarity-free, so conductors can be connected in either orientation. This is one of the practical advantages over strictly polarized fieldbuses.
How many meters can I put on one M-Bus segment?
It depends on the unit-load budget of your specific master and the unit-load rating of each connected device — always check the master's datasheet rather than assuming a generic number.
What's the difference between M-Bus and Modbus?
They are unrelated standards despite the similar name. M-Bus (EN 13757) is a dedicated European standard for utility metering — heat, water, gas, electricity. Modbus is a general industrial fieldbus used across drives, PLCs and inverters. Gateways can bridge the two, but they are not interchangeable protocols.
When should I add a repeater instead of more cable?
When the segment's unit-load total or cable run approaches the master's rated limit. A repeater or level converter splits the load across two segments instead of overloading one long run.
Is wireless M-Bus a replacement for wired segment planning?
Not exactly — wM-Bus (EN 13757-4, 868 MHz, modes S/T/C) removes the cabling step but still needs planning around addressing, mode selection and reception, so documentation discipline stays the same.
Planning an M-Bus rollout?
Send us your meter count and building layout — our engineers will help size segments, place repeaters, and check your master's capacity before you order cable.