How to plan power supply for your NMEA 2000 network

Learn how to create a network diagram, calculate LEN, and choose the right power insertion points for a stable and safe installation.

Powering an NMEA 2000 network doesn't have to be complicated, but proper planning saves time and reduces problems during installation. Here, we cover the basics of power supply, network diagrams, LEN, and power insertion points.

Why is a network diagram important?

The first step is to create a network diagram showing all cables, connectors, and devices. It doesn't have to be exact or to scale – a hand-drawn diagram is sufficient. The diagram is crucial for:

• Calculating voltage drop
• Planning power insertion points
• Identifying cable lengths and LEN values

At a minimum, the diagram should include cable lengths, power insertion point(s), LEN (Load Equivalency Number) for each device, and the single grounding point connected to the vessel's RF ground.

Understanding LEN (Load Equivalency Number)

LEN indicates how much current a device draws from the network. Each certified NMEA 2000 device has a LEN value specified by the Manufacturer. This is used in voltage drop calculations according to Ohm's Law.

1 LEN = 50 mA, meaning 20 LEN corresponds to 1 A. Devices over 20 LEN (1 A) should not be powered from the NMEA 2000 bus but should have their own power supply. For example, MFDs usually have separate power supplies.

The higher the LEN, the greater the voltage drop. Therefore, place high-power devices near the power insertion point to minimize cable length and voltage loss.

Power insertion points and voltage requirements

NMEA 2000 devices typically require 9–16 VDC (some up to 24 V). All devices draw some current from the bus via their transceiver, even if they have a separate power supply for functions like displays.

Common power sources:

• Battery connection 12.6 VDC
• Mains power supply 13.8 VDC (same Manufacturer for multiple units)
• AC/DC converter 13.8 VDC
• DC/DC converter 13.8 VDC

Placement of power cable

Placement depends on the network design. A power-tee feeding both sides of the backbone should be placed near the center. If high-power devices are at one end, place the power cable closer to them. Small networks can be powered from one end via a simple power cable and a 4-way tee.

In large networks, multiple power insertion points may be needed to keep the voltage above 9 V. All power sources must be from the same Manufacturer and properly fused.

Grounding and safety

The network should always be grounded at a single point to avoid ground loops that interfere with communication. Use the correct fuses for the power connection and check polarity.

Quick diagnostics with smart terminators

Products like Actisense A2K-TER-U can provide quick visual feedback on the voltage level. LEDs indicate if the voltage is correct (green), low (red), or if the polarity is wrong. This saves time during troubleshooting compared to using a multimeter.

Summary

Plan your NMEA 2000 network carefully with a diagram, calculate LEN and voltage drop, choose the right power sources and placement. Follow NMEA standards and use diagnostic tools for a safe and stable installation.