What Is an M12 L-Coded Connector?

An M12 L-coded connector is an M12 power coding for DC supplies, rated up to 16 A at 63 V. It is defined in IEC 61076-2-111, the M12 power standard, and has four power contacts plus, on 5-pin versions, a functional earth.

L coding lets M12 carry real power. Where an A-coded connector suits a sensor supply of a few amps, an L-coded connector feeds whole I/O modules, valve islands and devices, and can daisy-chain that power from one device to the next. Its distinct key stops it being mistaken for a signal or Ethernet connection, and its larger contacts keep the voltage drop and heating low at high current.

It was introduced largely for PROFINET, to replace the bulkier 7/8 inch power connectors used on earlier fieldbus systems with something the same size as the data connectors beside it.

PROFINET uses L coding to carry two separate 24 V circuits in one cable. The assignment below follows the PROFINET installation guidelines.

Keeping the two circuits apart lets a safety system switch off the actuator supply, so valves and outputs go dead, while the module electronics stay powered and keep reporting diagnostics. Other industries use the same connector with their own assignments, so check the device datasheet before wiring.

The 16 A rating applies to the connector. Reaching it also needs cable of around 2.5 mm² per core; cables with 1.5 mm² cores are typically rated nearer 10 A. Ratings are usually given at around 40 °C, so expect to derate in hot cabinets or direct sun.

Voltage drop is the limit people meet first. Copper cable with 1.5 mm² cores has a resistance of roughly 0.012 ohm per metre per core, so a 20 m run has around 0.48 ohm in the loop. At 10 A that loses nearly 5 V, a fifth of a 24 V supply, before the last device in a daisy chain sees it. Shorter runs, thicker cores or a second feed point fix it.

Both can carry a 24 V supply, but they suit different loads. A-coded connectors are typically rated around 4 A and suit a single computer, sensor or small device. L-coded connectors carry up to 16 A and suit distribution, where one cable feeds several devices or a device that draws more than an A-coded contact can handle. The two will not mate, so a site can run both without risk of mixing them up. The other DC and AC power codings, T, S and K, are compared in our guide to M12 power codings.

PROFINET I/O modules usually have two L-coded power connectors: a male input and a female output. Power arrives on the input and passes straight through to the output, so one supply cable can feed a row of modules along a machine. The female output keeps the live contacts recessed when nothing is plugged in.

The catch is that the first connector in the chain carries the current for every device after it. With a 16 A limit per contact, the chain has to be planned: add up the load on 1L+ and 2L+ separately, keep the total below the rating of the first connector and the cable, and add a second feed point when it does not fit. Protect each feed with its own fuse or electronic circuit breaker, so a fault on one branch does not take down the whole line.

Most industrial computers draw a modest current and take their DC input on a smaller M12 coding. L coding appears where the input current is higher: our IP69K computers with PoE+ camera ports, and rugged GPU computers with a discrete graphics card, often use an L-coded power input, because the PoE output or the GPU pushes the supply current beyond an A-coded rating at 24 V. Our guide to M12 waterproof connectors explains why sealed power connectors matter on these systems.

We supply higher-power rugged computers with L-coded or other M12 power inputs as standard, and we size the power cable for the current and run length of your installation before the system ships.