How to make a BAS network riser diagram

Controls specs (Division 23 09 00 or 25) list the riser as a required item of the submittal. A typical guide specification asks for a network riser diagram showing:

• wiring types and network protocols;
• the locations of floor penetrations and the number of control panels;
• each control panel labeled with its network address and BACnet device instance number;
• every router, switch, hub and repeater.

Some owners go further. UC Santa Cruz, for example, asks for a separate riser for every supervisory controller, listing the protocols each one uses. Read your own spec first: the riser is checked against it line by line.

Most current specs describe two levels. Building controllers, operator workstations and large equipment sit on a BACnet/IP backbone over Ethernet. Field controllers on each floor or system sit on BACnet MS/TP trunks (RS-485), each connected to the backbone through a router. Central plant controllers and large air handlers usually stay on the IP backbone.

The riser makes that structure readable: floors as horizontal bands, panels where they really are, the IP backbone running vertically through the penetrations, and each MS/TP trunk drawn from its router to the last device on the run.

1. List the controllers. Start from the equipment schedule and the points list: one line per controller, with the floor and the room or panel it sits in.
2. Assign each controller to a network level. Plant and large air handlers on BACnet/IP, terminal units and small equipment on MS/TP.
3. Split the MS/TP trunks. Keep each RS-485 segment within its limits: no more than 32 devices and 4,000 ft per segment without a repeater, and around 60 devices per MS/TP network in practice, depending on traffic.
4. Number everything. MS/TP MAC addresses, device instances and network numbers, following the rules in BACnet addressing.
5. Draw floors, panels and penetrations. Show where each cable crosses a floor, where each router and switch lives, and the end-of-line termination on each trunk.
6. Label and cross-check. Every panel carries its address and device instance; every controller on the riser appears in the points list, and the other way round.

• Duplicate device instances. The device instance must be unique across the whole BACnet internetwork, not only on one trunk. Duplicates break device discovery.
• Gaps in MS/TP addresses. Many specs require MAC addresses to start at 0 and run without gaps, with Max Master set to the highest address on the trunk.
• Missing network gear. Switches, routers and repeaters are part of the riser. Reviewers reject drawings that leave them out.
• A riser that drifts from the points list. When equipment is added or moved during the job, the riser and the points list have to change together, or the as-builts will not match the site.

In Structio you describe the building once: floors, rooms, equipment and controllers. Structio draws the network diagram and builds the points list from that same project, so a change on the job shows up in both. Any controller brand. See how it works.