What Is M-Bus? A Plain Explanation
M-Bus (Meter-Bus, EN 13757) is the European standard used for remotely reading heat, water, gas and electricity meters. You'll most often meet it if your building or apartment already has a centralized metering system you'd like to connect to your own home automation.
How M-Bus Works
A standard for meter data
M-Bus (EN 13757) was built specifically for collecting heat, water, gas and electricity meter data — most commonly in buildings and apartment blocks.
A simple two-wire bus
Wired M-Bus runs on a low-voltage, polarity-free two-wire bus — you can connect the wires either way round. The master powers the bus (typically around 36V), and meters reply using current modulation.
Every device gets an address
Primary addressing uses a number from 1–250; secondary addressing uses a unique 8-digit ID. That lets you address a specific meter even in a large installation or after a meter swap.
The wireless variant — wM-Bus
Wireless M-Bus (EN 13757-4) runs in the 868 MHz band in the EU, with modes S, T and C — depending on how often the meter transmits and how long its battery needs to last.
Facts You Should Know
The European standard for utility meter reading
M-Bus's physical/link layer is defined in EN 13757-2, its application layer in EN 13757-3. It's not a brand or a single product — it's an open European standard.
A cheap, simple meter side
Meters (slave devices) don't generate their own voltage — they reply using current modulation powered by the master. That keeps the meter side cheap and simple to build.
Two addressing modes
Primary addressing (1–250) and secondary addressing (an 8-digit ID built from manufacturer code, serial number, version and medium type) — the second is handy when meters get replaced or installations are large.
Segment and unit-load planning
Bus sizing is planned around a 'unit load' budget. Repeaters/level converters let you extend a segment — but exact numbers depend on your specific master model, so check its documentation.
Typical devices on the bus
Heat cost allocators for radiators, water meters, heat meters, gas meters and electricity meters — often feeding a building's or property manager's centralized metering software.
Gateways to other protocols
Gateway devices convert M-Bus/wM-Bus data to protocols like Modbus or BACnet, so meter readings can reach a BMS or KNX system without reading M-Bus directly at every device.
What to Check Before You Start
M-Bus is rarely 'plug in and read' — especially on shared building networks. Here's what to figure out before you buy anything or connect.
- Whether your meter actually has an M-Bus output — not a pulse or Modbus output
- Whether the bus belongs to you or the building manager — shared networks usually need permission
- An M-Bus-to-USB or M-Bus-to-IP converter to read the data on a computer or automation system
- Whether you know the meter's address (primary or secondary) — reading won't start without it
- Software or a home automation platform that actually understands the M-Bus protocol
Frequently asked questions
Can I just connect to my building's M-Bus network?
Often not directly — if it's a shared network (say, a heat substation in an apartment building), you'll usually need the building manager's permission and coordination. It's not a simple plug-and-read sensor like some consumer gadgets.
What's the difference between M-Bus and Modbus?
They're two completely different standards, even though the names sound alike. M-Bus (EN 13757) was built specifically for utility meter reading. Modbus is a general-purpose industrial protocol used across a huge range of devices — drives, PLCs, solar inverters. Some meters offer both outputs, and gateways can convert between them, but they aren't interchangeable without a converter.
Is M-Bus wired or wireless?
Both. Wired M-Bus runs on a two-wire bus. The wireless variant (wireless M-Bus, wM-Bus, EN 13757-4) runs in the 868 MHz band in the EU and is common for battery-powered meters.
How many meters can one M-Bus bus support?
That depends on your specific master device and its unit-load budget — always check the master's documentation for the exact number or maximum cable length rather than assuming a general figure.
Why would a DIY enthusiast even run into M-Bus?
Usually because their building or apartment already has centralized heat or water metering, and they want that data in their own home automation setup — that's when they discover the meter speaks M-Bus rather than, say, a simple pulse output.
Ready to Start Reading M-Bus Data?
Browse M-Bus converters and accessories in our shop — or get in touch if you're not sure where to start. No pressure, just honest advice.