Example BACnet Network Number & Instance Number Convention

When I assign a BACnet instance number or BACnet network number, I never use the defaults provided by whatever product I’m using.

A few moments of thought about some kind of standard for your site can save you a lot of time down the road when you want to expand your system to include more devices. You don’t know quite how your networks will expand; I’ve had to merge two separate hospital BACnet networks that were addressed without any particular guideline and it was a mess. Nobody thought that the hospitals would merge when the networks were created, so people felt free to use random numbers for every new device.

Here’s a sort of guideline you can use to decide how to plan your own network. It’s certainly not gospel, and if you think of a better way of going about it please let me know.

BACnet Network Number Convention

Keep in mind that the maximum valid network number is 65535.

Building # (2 digit) – Floor # (2 digits) – Trunk # (1 digits)

Example: 01253

This would be a BACnet network in building 1, on floor 25, and it’s trunk number 3 on that floor.

BACnet Instance Number Convention

Keep in mind that the maximum instance number is 4,194,302.

Building # (2 digits) – Floor # (2 digits) – Device Marker (1 digit) – Device Index (2 digits)

For device marker, I use 0 as some kind of supervisory device.

Supervisory devices are primarily used as a graphics interface or historian. They aren’t directly responsible for control.

I use 1 as some kind of field controller directly responsible for control or monitoring.

I use 2 as some kind of gateway that converts to kinds of media, like MS/TP to BACnet/IP.

You can be creative here and think of ways to describe the particular kind of hardware you’re using. I think it’s useful to have that described in the instance number, but that’s arguable.

The device index is something like a controller number or some kind of arbitrary device index number that makes it unique.

Summary

If you spend a few minutes working on a device and network number convention, you’ll have a lot less trouble in the future. Only doing one controller in a building? Still follow a convention like the above. When it comes time to integrate that building with a wider network you’ll surprise the people that come after you with your uncanny abilities of foresight.

It costs you little, and saves so much time later.