Which M12 Codings Are Used for Power?

An M12 power connector is an M12 circular connector with a coding, contacts and ratings designed for supply current rather than signals. The power codings L, T, S and K were added in IEC 61076-2-111 so that M12 could replace larger power connectors on machines, such as the 7/8 inch and M23 types, and so that power and data could use connectors of the same size.

Each power coding has its own key, so a power cable cannot be connected to a signal or Ethernet socket, and an AC cable cannot be connected to a DC socket. The contacts are larger than on signal codings, and the AC codings add a protective earth contact that mates first and breaks last.

The ratings below are typical maximums from the standard and connector datasheets. The cable and the operating temperature usually set a lower practical limit.

L-coded connectors, the most widely used of the four, are covered in depth in our L-coded M12 guide.

L and T coding both carry DC up to 63 V, which covers the 24 V and 48 V supplies used on machines, vehicles and telecom equipment. L coding carries more current and is the PROFINET standard, with two separate 24 V circuits in one cable. T coding has four contacts rated up to 12 A and is common on compact switches and I/O. Several of our M12 Ethernet switches take redundant 24 to 55 V DC inputs on a 4-pin T-coded connector.

The higher input voltage on those switches is deliberate. PoE needs around 44 to 57 V at the port, so a switch fed at 48 V can pass power through to its PoE ports with little conversion, while one fed at 24 V has to boost it. Feeding at the higher voltage also halves the current for the same power, which shrinks the voltage drop on a long M12 power cable. Redundant inputs on two separate connectors let the switch keep running if one supply or cable fails.

S and K coding carry AC mains voltages up to 630 V. S coding has three contacts plus protective earth for single-phase loads, and K coding has four plus earth for three-phase loads such as motor drives. Both replace the older C coding for new designs.

In practice the AC codings also turn up on DC equipment. Some rugged and outdoor computers take a 9 to 36 V or 9 to 60 V DC input on an S- or K-coded connector, because the larger contacts and distinct key suit a vehicle or outdoor supply. The coding tells you which plug fits, not what voltage the socket expects, so always read the datasheet before connecting a supply.

Power cables are where M12 mistakes are most expensive, because the wrong cable can damage equipment rather than simply not working. Check these points against the datasheet of the device:

Most industrial computers take a low-voltage DC supply through a 4- or 5-pin M12 connector, from 9 V up to 110 V on railway models, because the current is modest. A coding is common, but our catalog shows K, S, L and even B coding used for the same job by different makers. Higher-current systems, such as IP69K computers with PoE+ ports, use L coding.

Our EN 50155 railway computers and in-vehicle computers add wide input ranges and ignition sensing on the same power connector. Our guide to M12 waterproof connectors covers sealing and connector choice.

We supply our rugged, railway and vehicle computers with the M12 power input and a matched power cable as standard, sized for your supply voltage, start-up current and cable run.