Look through the parts for a Garmin SERV system and you see two network names: RV-C and NMEA 2000. Both run on CAN bus, the same kind of two-wire data network used in cars, so it is easy to assume they are one network. In a Garmin SERV installation they are kept apart, and Garmin's install guide says so. This guide explains what each network is, which Garmin parts belong to which, and where the adapter cables and the RV-C multi tap fit.
The short version
- RV-C is the RV industry's network. The RV Industry Association describes it as a standardized, open communication protocol for recreational vehicles, built on the CAN bus framework, and an industry-wide recommended practice.
- NMEA 2000 is a plug-and-play communications standard that started on boats. Garmin uses the same NMEA 2000 micro connectors, cables, T-connectors and terminators for its own CAN backbone, which is where NMEA 2000 EmpirBus modules such as the Connect 50 connect.
- Keep them separate. Garmin's SERV install guide warns: do not combine the Garmin main CAN bus with the RV-C bus. Doing so can damage property or stop the display working properly.
Side by side
| Garmin CAN / NMEA 2000 backbone | RV-C | |
|---|---|---|
| What it is | Plug-and-play CAN standard, used by Garmin for its own network | Open RV industry protocol on CAN, from the RV Industry Association |
| Garmin parts in our range | NMEA 2000 starter kit, 4 m backbone/drop cable, 4-pin CAN to NMEA 2000 adapter | RV-C multi tap, RV-C interior temperature sensor, Mini-Fit to bare wire cable |
| Connectors | NMEA 2000 micro connectors (isolated Connect 50 models have a Micro 5-pin M12 male) | Molex Mini-Fit in Garmin's RV-C wiring |
| Layout | A straight backbone with T-connectors and a terminator at each end | Devices join at the RV-C multi tap in Garmin's diagram |
| Typical devices | NMEA 2000 EmpirBus modules; the display's CAN connection (or the RV-C multi tap, per your wiring plan) | Coach systems on RV-C, such as the interior temperature sensor |
The bridge between them is a cable: the NMEA 2000 to RV-C adapter cable (3 m), which goes from an NMEA 2000 connector to an RV-C CAN connection. Which device it goes on depends on the wiring plan for your coach. Don't treat it as a way to merge the Garmin main CAN bus and the RV-C bus into one network: Garmin's guide warns against exactly that.
How the Garmin NMEA 2000 backbone is built
Garmin's NMEA 2000 technical reference lays out the rules, and the SERV install guide's "basic CAN network" drawing uses the same parts: the display through a CAN adapter, a T-connector per device, drop cables, a CAN power cable and a male and female terminator.
- Every device joins through a T-connector, using the top of the T. T-connectors join one another only by their sides.
- A terminator goes on each end: one male, one female. Never more than two terminators on the network.
- A drop cable can be up to 6 m (20 ft). Cables up to 6 m can serve as backbone or drop.
- Power comes in through a dedicated NMEA 2000 power cable at 12 V DC, through a switch so it can't drain the battery. Devices run from 9 to 16 V DC.
- Limits: 100 m (328 ft) between any two points, 78 m (256 ft) of drops in total, 50 devices.
The NMEA 2000 starter kit covers a basic backbone in one box: a 2 m drop cable, a 6 m backbone cable, a 2 m power cable, 2 T-connectors and male and female terminators. With two T-connectors, one top takes the power cable and the other takes one device. Each extra device needs another T-connector.
Voltage drop on longer runs
Garmin's reference says the supply voltage may not drop more than 1.67 V between the power T-connector and the farthest device. It gives the formula: voltage drop = 0.053 (ohms per meter, Garmin cable) x distance in meters x total load in LEN x 0.1, where 1 LEN is 50 mA. Garmin's worked examples measure 22 to 24 m from the power connection to the farthest device; if your run is long and feeds many powered devices, do the sum, and if it comes out above 1.67 V, connect power in the middle of the backbone. Garmin's data sheet says its isolated Connect 50 models draw zero load from NMEA 2000 bus power.
How the RV-C side connects
Garmin's SERV install guide has a second drawing for "Mini-Fit CAN". There, the display and a module connect through CAN adapters and 22 AWG drop cables to an RV-C multi tap. Garmin notes that the cables in that system connect to the multi tap with male connectors, and can be extended with female connectors (not included). The Mini-Fit CAN pins are:
| Name | Wire color | Function | Molex pin |
|---|---|---|---|
| NET-H | White | Signal (twisted) | 1 |
| NET-L | Blue | Signal (twisted) | 2 |
| NET-C | Black | Ground | 3 |
| NET-S | Red | Power | 4 |
Garmin says the power and ground wires on the Mini-Fit CAN connector are optional, because the display has its own power harness. Use 22 AWG wire to extend it. The Mini-Fit to bare wire cable is for landing that kind of connection on terminals or a device without a Mini-Fit plug.
Where the SERV+ fits
A SERV+ is the only display in the range with RV-C on its own wiring. Its 8-pin input/output harness connects the RV-C and LIN data buses along with the 5 configurable inputs. A SERV connects through its CAN port and a CAN adapter, as in Garmin's drawings (SERV vs SERV+ covers the other differences). Both displays also have Ethernet, which Garmin uses to link several screens.
Which parts do I need?
| Your coach has | Start with |
|---|---|
| No network yet, and you are adding EmpirBus modules | NMEA 2000 starter kit, a 4 m drop per module, the CAN adapter for the display |
| An RV-C network you want the screen to see | RV-C multi tap, the NMEA 2000 to RV-C adapter where your plan calls for it, Mini-Fit to bare wire for odd devices |
| Both | Two separate networks, each with its own parts. Don't join the Garmin main CAN bus to RV-C |
| Want cabin temperature on screen | RV-C interior temperature sensor |
If you're not sure what your coach has, send us photos of the existing wiring and the part numbers on any modules. We'll help you sort out which side each device is on. For the full parts list see what you need to install a SERV or SERV+. Everything ships from our warehouse in Upland, California. Browse the full Garmin SERV range. Found it cheaper? We'll beat it.
FAQ
Is RV-C the same as NMEA 2000?
No. Both use CAN bus, but they are different protocols for different industries. In a Garmin SERV system they are separate buses.
Can I join the RV-C bus and the Garmin CAN backbone with an adapter cable?
Garmin's install guide says not to combine the Garmin main CAN bus with the RV-C bus. Plan which network each device belongs on before you choose adapter cables, and ask us if you are unsure.
Do I need terminators on the NMEA 2000 backbone?
Yes, exactly two: one male and one female, at opposite ends. The starter kit includes both.
Can I power the backbone straight from the battery?
Garmin says no: power it through the ignition or an in-line switch, or it will drain the battery when the RV is not in use.