Voltage drop calculations in NMEA 2000 networks – How to do it right from the start

Learn what voltage drop is, why it affects your network, and how to calculate it correctly for stable and safe operation.

For your NMEA 2000 network to function correctly, it is important to understand voltage drop and how the power supply affects the network. This guide explains the basics, why the calculations are important, and how to perform them.

What is voltage drop?

Voltage drop is the voltage lost along the network's backbone as current passes through cables and devices. The further the distance from the power input point, the greater the voltage drop. This is affected by:

• Available voltage
• Type of power supply
• Cable resistance and length

The purpose of the calculations is to ensure that all devices receive sufficient voltage to function correctly.

Placement of power sources

There are two common ways to supply power in an NMEA 2000 network:

• End-fed – The power supply is located at one end of the backbone and feeds in one direction.
• Mid-fed – The power supply is located near the middle and feeds in both directions.

In larger networks, several isolated power sources may be needed. These must be of the same Brand and model, and installation should be performed by a certified NMEA installer. If you have multiple power sources, it is important that they do not feed against each other – for example, an additional power source on the right side should only be connected to that side.

Calculation of voltage drop

Voltage drop is calculated using Ohm's Law:

E = I * R
VD = 0.1 * NL * BL * Cable Resistance

Where:

• NL = Total network LEN (number of devices)
• BL = Backbone length in meters
• Cable Resistance = depending on cable type:
  • Lite: 0.057 Ω/m
  • Mid: 0.015 Ω/m
  • Heavy: 0.012 Ω/m

Example calculation

NL = 10, BL = 12.5 m, Cable Resistance = 0.057 Ω/m

VD = 0.1 * 10 * 12.5 * 0.057 = 0.71 V

If the network is mid-fed, calculations must be done separately for each side.

When are segment calculations needed?

Segment calculations are used when the voltage drop risks exceeding limit values (e.g., 1.17 V for battery operation or 3.61 V for 13.8 VDC). In this case, the network is divided into sections and each segment is calculated individually.

• When the initial estimate is close to the limit value.
• When flexibility is required for device placement.

Tips for correct installation

• Plan power input carefully.
• Use the correct cable type and length.
• Follow NMEA guidelines for loss budget.
• If in doubt – hire a certified NMEA installer.