Do you need a kit?
Often not. If your boat already has an NMEA 2000 network, it already has a backbone, terminators and a power feed, and a new device is added by dropping a cable from a spare T-connector. A kit is for three jobs: building a bench network to test a gateway or a Signal K server before it goes aboard, building a small network from scratch on a boat with none, and replacing damaged cable. If you are choosing the computer that will read the bus, start with our onboard computer guide, and see Powering a boat computer for the 12 V side.
This is buyer's research from makers' pages and published guidance, not an installation manual. We haven't bench-tested these kits. For a boat with an existing network, or any wiring you are unsure about, follow the manual of your equipment and ask an installer.
How the network is built
NMEA 2000 is a CAN bus. Everything hangs off one backbone cable, and every device connects to the backbone through a T-connector and a short drop cable. Both ends of the backbone get a terminator, and the network gets one power feed of 12 V. The same cable carries data and power, which is why a single bad connector can take out the lot.
Micro-C and Mini-C
Two connector families are sold. Per Maretron, they are electrically the same with the same pin-out; the difference is size and current. The Micro/Mid system is generally used for smaller networks under about 4 A per leg, and the Mini system for larger ones between 4 and 8 A. Mini-to-Micro adapters exist, but check them before you mix families. Small-boat gear, and the kits here that state a connector type, is Micro-C.
Other brands
Raymarine's SeaTalkng uses its own connectors and needs Raymarine's adapter cables to join an NMEA 2000 backbone. Raymarine's guidance is to use its original adapters and not to duplicate the power or grounding of the joined networks, so a mixed network still gets one power feed. We did not find sourced guidance for Navico's SimNet, so check Simrad's documentation before buying adapters.
The limits
Garmin's NMEA 2000 technical reference sets the rules most makers follow:
- No more than 100 m between any two points on the network, measured between the terminators plus the drops at the two ends.
- No single drop longer than 6 m, and no more than 78 m of drops in total.
- No more than 50 devices.
- A supply voltage that drops by no more than 1.67 V between the power T-connector and the farthest device. Panbo cites the specification as allowing 1.5 V between any two devices, so the lower number is the safe one.
Garmin gives the drop as resistance × distance × load × 0.1, with 0.053 ohm per metre for its cable, the distance in metres from the power connection to the farthest device, and the load as the sum of the devices' LEN numbers. A LEN of 1 is 50 mA. Its worked example, 22 m with a LEN total of 14, gives 1.63 V, which passes. If the answer is over 1.67 V, power goes in the middle of the network. A small bench network never gets near these limits, but a long boat can.
Powering the bus
The bus is powered from a fused 12 V supply through a power T-connector or a power cable into a T. The fuse is where makers differ: a Panbo comparison reported that Garmin specifies 3 A on its power tap and Simrad 5 A, and one retailer's power cable says the backbone must be fused at 3 A or less. Use the value in the manual of your power cable, and fuse close to the supply, as in our fusing section. The bus needs at least 9 V at each device, per Panbo's reading of the specification, so a sagging helm supply is a real fault to check.
Connect power at one point only, unless the network is long enough to need the middle. A second feed from another supply, or a second ground, is a common way to create odd faults and ground loops.
The three kits
All three bring up a small network. Which one depends on whether you want more cable, documented contents, or a fuse in the box.
Garmin NMEA 2000 Starter Kit — the most cable for the money
Retailer listings agree on the contents: a 6 m backbone cable, a 2 m drop cable, a 2 m power cable, two T-connectors and one male and one female terminator. That is enough for a small network of two or three devices, and the longer backbone suits a bench or a small boat. Listings disagree on whether the power cable has an in-line fuse holder, so confirm that on the box or fit your own. We could not open Garmin's product page, so treat the contents as unverified until you do.
Strengths
- Longest backbone cable of the three
- Has a male and a female terminator, the pair most networks need
- Widely stocked, usually near $100–$120
Trade-offs
- Contents come from retailers, not a maker page we could open
- Fuse holder on the power cable is disputed between listings
- Connector type is not stated on the listings we saw, so confirm it is Micro-C
Actisense A2K-KIT-1a — documented by the maker
Actisense's own page lists a Micro power T-piece, two male Micro terminators, two Micro T-pieces and a 2 m Lite cable assembly, with metal bodies and nickel-plated brass pins, for a basic two-device network. It is the kit to buy if you want every part number documented, and it is in the Micro connector family used on most small-boat gear. The cable is short, and a search summary of Actisense's range says its Kit 2a swaps the 2 m cable for a 6 m one, which is the more practical build. When we looked the maker page showed it out of stock, and a reseller listed it at about $162.
Strengths
- Maker publishes contents, part numbers and materials
- Metal Micro connectors with a dedicated power T
- From the maker of the gateways in our gateway guide
Trade-offs
- Only a 2 m cable in the 1a kit
- Maker page showed out of stock, and a reseller charges more than Garmin's kit costs
- Two male terminators, so check genders against your devices
Digital Yacht NMEA 2000 Starter Cable Kit — fused power in the box
Retailer listings describe a smart 4-way T-piece "backbone", a 1 m power cable with an in-line fuse, a 1 m drop cable and a pair of removable terminators, in Micro-C connectors, for up to three devices. The built-in fuse is its selling point: fusing is left to you or unclear in the other two kits. With no real backbone cable it is a bench or very small boat kit, which the listings say you can expand with more standard Micro-C parts. We could not open Digital Yacht's own page, and prices ranged from about $119 to $140 across retailers.
Strengths
- In-line fuse on the power cable
- Compact, with fewer connections to fail
- Micro-C, so you can extend with standard parts
Trade-offs
- Three devices and no backbone cable
- Priced like the Garmin kit for less cable
- Maker page not confirmed by us
Testing the bus
A multimeter finds most faults. Power the network off and measure between CAN-H (white) and CAN-L (blue): a healthy network reads about 60 ohms, which is the two 120-ohm terminators in parallel (Panbo, 2021). A reading near 120 ohms points to a missing terminator or a loose or broken backbone connection, and a reading around 40 ohms would mean a third terminator, since three 120-ohm resistors in parallel give 40. Some devices switch on an internal terminator in software after power-up, so a resistance test does not catch them.
With power on, measure between the black (ground) and red (power) wires at several points along the bus. The voltage should stay above 9 V and not sag far along the cable. Panbo's guide suggests a breakout cable for the meter probes and shows Actisense's A2K-TER-U terminator, which has an LED that goes green above 9 V. Field-attached connectors are a common failure point, so use heat-shrink on bare conductors.
Shopping list
All Amazon links go to searches, so check the seller and the exact model on the listing.
Garmin NMEA 2000 Starter Kit · Actisense A2K-KIT-1a · Digital Yacht starter kit
Micro T-pieces · Terminators · Drop cables · Backbone cable · Field-attachable connectors · Power cable
Frequently asked questions
What is in an NMEA 2000 starter kit?
A starter kit is the minimum parts for a small network: T-connectors, a backbone or drop cable, a power cable or power T-piece, and terminators. The three kits here differ. Actisense lists a power T, two T-pieces, two terminators and a 2 m cable on its own page. Retailer listings describe Garmin's as a 6 m backbone, 2 m drop, 2 m power cable, two T-connectors and two terminators.
How many terminators does an NMEA 2000 network need?
Exactly two, one at each end of the backbone. Powered off, the bus should read about 60 ohms between CAN-H and CAN-L, which is two 120-ohm terminators in parallel. A reading near 120 ohms suggests one is missing and a reading near 40 ohms suggests a third.
How long can an NMEA 2000 backbone be?
Garmin states no more than 100 m between any two points, with drops of no more than 6 m each and 78 m in total, and no more than 50 devices. Cable makers publish their own figures for light and heavy cable, so check yours for longer runs.
Can I add a gateway or USB adapter to an existing network?
Yes, and you normally should not buy a kit for it. Plug the gateway into a spare T-connector with a drop cable. A gateway such as those in our gateway guide is a device on the bus like any other, so it needs no extra power feed if the bus already has one.
What fuse does the NMEA 2000 power cable need?
Follow the instructions for your power cable. One retailer's power cable says to fuse the backbone at 3 A or less, and Panbo reported that Garmin specifies 3 A and Simrad 5 A on their power taps.
What is the difference between Micro-C and Mini-C?
Per Maretron they are electrically compatible with the same pin-out. Micro is the smaller, lighter cable for smaller networks, and Mini is the larger one for bigger loads. Adapters exist between the two.
The short version
Most cable for the money: the Garmin starter kit, with its 6 m backbone and two terminators.
Documented parts: the Actisense A2K-KIT-1a, or its longer-cable 2a version.
Fuse in the box: the Digital Yacht kit for a three-device bench or tiny boat.
On a boat that already has a network: skip the kit. Add a T-piece and a drop cable.