Douglas Krantz - Technical Writer - Describing How It Works

What is a Riser Diagram?

By Douglas Krantz | Descriptions

What is a Riser Diagram?

What is a Riser Diagram?

Greetings Douglas,

I'm installing a fire alarm system, but I'm told I need wiring details for the NAC [Notification Appliance Circuit] and the SLC [Signaling Line Circuit] loop. Please explain.

Thank You, DR

Riser Diagram

I'm guessing that the requirement for the Notification Appliance Circuit (NAC) wiring details is to show how you are planning to power all the horns and strobes. The wiring details also have to show how the Signaling Ling Circuit (SLC) or SLCs will connect to the detectors and modules.

The reason for requiring this information for the NAC circuits, and the SLC loops is that if they aren't planned out in detail before stringing any wires, some of the devices won't work, and some of the horns or strobes won't completely work, especially during a power blackout. The wiring details are the design that you plan on using for the circuits.

Even though they can't help with the building layout, almost always, the technical support team for the manufacturer will be able to provide worksheets to figure out some of the details of the design. When working with the worksheets, always make copies of the worksheets and work only with the copies. It's much easier to start over with a new copy of a worksheet than it is to get a new worksheet from technical support. You can count on changing the design (and the worksheets) several times before coming up with a final design.

Even if the worksheets are all on the computer, make a copy of the computer file and work with the copy of the file.

First, though, so you know what you're working with, you have to create a Riser Diagram.

NAC Riser Diagram

In the past, the design engineer for buildings that you've worked with have provided prints of the system design. There should be a "Riser Diagram" showing all the equipment, each circuit, and each device like the horns and strobes connected to each circuit. The Riser Diagram isn't a wiring diagram, and it's not really a building layout diagram, it's a block diagram showing the signal paths of how equipment and devices are connected together.

On buildings that you've already wired, look at the Riser Diagram; study the Riser Diagram. In many respects, it is the basis for the rest of the fire alarm system design.

That diagram is for two purposes. One purpose is to show others what will be done, like showing the installer what devices will be on which circuit and showing the fire department planners how the circuits will be used.

The other purpose is more important. The other purpose is to show the design engineer, the one who's designing the system, how it's going to work. As an example, it might be that there are too many horns or strobes on a circuit. That's easily seen on the Riser Diagram. If that's the case, the Riser Diagram has to be changed. It's far easier to move the devices to another circuit when working with paper or the computer (like the diagram) than to try rewiring the building to move the wiring or the devices. In other words, if there's a design problem, it's easier to fix the design (Riser Diagram) that it is to fix a finished building.

The main purpose of the Riser Diagram is to help with the design in the first place, the secondary purpose of the Riser Diagram is to show others that the system is designed correctly, and to show the installers how to actually build the system.

When making the riser diagram, it would be a good idea to include the current that's being used for each horn or strobe. Later, the numbers, when added up for the NAC circuit, would be for your use when you check out the total current on the NAC circuit.

Both the NAC circuits and the addressable SLC circuits can be included on the same Riser Diagram.

NAC Worksheets

Once the Riser Diagram is completed, then you can fill out the worksheets. Each NAC circuit in the building has to be filled out on a worksheet. Filling out the worksheet for each NAC is the only way you can know that the NAC circuit is going to power all the devices on that particular NAC. It's also the way you can show others that you have worked it out.

SLC Riser Diagram

The SLC Riser Diagram is how you can determine which detectors and modules go on each SLC.

Each module and each detector has its own address or addresses. Alongside the detectors and modules, you need to show the address for each device. That way, you can make sure that there aren't too many addresses assigned to a SLC Loop.

When you make the Riser Diagram, leave yourself some extra unused addresses. You will make additions, so leave 20 or 30 addresses for each loop, at least, for expansion. You don't want to run an extra loop to another part of the building because you have discovered that you exceeded the number of addresses you need to install.

Show Your Work

Whoever is asking for the wiring details for the NAC and SLC circuits is looking for the Riser Diagram, and looking for the worksheets. It's a confidence thing. If the Riser Diagram and the worksheets are filled out correctly, there is confidence that the system is designed correctly, and probably will work.

Providing this paperwork for others will help you as you figure out what needs to be done.

Douglas Krantz
Life Safety
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