Douglas Krantz - Technical Writer - Describing How It Works

Can a Waterflow Switch and a Tamper Switch be on the Same Zone?

It was shown in older versions of NFPA 72 that the that a waterflow switch and a tamper switch could be on the same conventional zone. It did require, though, that the tamper switch couldn't prevent the alarm from getting through.

In the olden days, tamper switches used to be wired in series with the end of line resistor because fire alarm control panels didn't have a supervisory type of alarm.

Greetings Douglas,

Somehow...somewhere I recall I read an article that said that the Waterflow Switch and Tamper Switch shall not be connected in the same IDC (Conventional Initiating Device Circuit) because one can activate the other?

I've been looking, back and forth NFPA 72 with no success...

My this a design decision, or actually is this addressed in NFPA 72?

Thank you, JA

If you've inspected conventional fire alarm systems in older buildings, you may have run into a few of these.

The wiring issue is only indirectly addressed in the NFPA. The National Fire Protection Association (NFPA) is no longer in the business of specifying how to wire much of anything (wires don't detect fires or warn anyone); the NFPA is in the business of showing what is needed to:
  • Detect fires and warn people of fires (Fire Alarm)
  • Detect when other life safety systems are not normal (Supervisory Alarm)
  • Activate automatic protective measures when there's a Fire Alarm (Fire Doors, Smoke Control, etc.)

The NFPA also wants the building-wide fire alarm system to have internal checks so the system can be fixed in a timely manner; if there's an internal problem found with the fire alarm system, the panel should show a trouble.

Actions to Take - Four Conditions

Green Light Normal - The whole purpose of a fire alarm system is to tell people to take action. Even no action is an action. The first action that a fire alarm system tells people to take is "do what you normally do" because the fire alarm system is normal.

Red Light Alarm - If the fire alarm system has detected a fire, the action that the system tells everyone to take is "immediately take action to protect yourself" because there is a dangerous situation.

Yellow Light Supervisory - If something isn't right with a life safety system, the fire alarm system tells the building owners to "look around and put back to normal whatever life safety equipment isn't correct". In this case, the sprinkler system is not the fire alarm system, but because the sprinklers are a life safety / property protection system, the fire alarm system is supervising the sprinklers. If the water is turned off, the building owner should know about it and put the sprinkler system back to normal.

Yellow Light Trouble - If something is wrong with the fire alarm system itself, the fire alarm system tells the building owner to "fix the fire alarm system" because the fire alarm system might not detect fire, or warn people of fire.

Before Supervisory

In the olden days (before the 1960's) there was no such thing as a supervisory signal. In order to detect a closed valve, the tamper switch would "break" the wire going to the waterflow switch's end of line resistor. This tamper switch action causes a "trouble" for the fire alarm system.

Of course, there was a requirement that closing any valve tamper switch could not prevent a flow switch from sending an alarm. So that the waterflow switch could still work, the only wire that could go to a valve tamper was the wire to the end of line resistor. The wire between the waterflow switch and the panel was sacred; it had to be able carry the alarm signal, no matter what.

See "Why Does Closing Some Gatevalves Show Trouble?"

The left-hand part of the diagram shows the grandfathered - old - method of wiring a tamper switch. The old method only showed that the fire alarm system needed to be fixed. What is meant by "grandfathered" is that at one time this wiring was about the way to wire a tamper switch. If it was installed at the time it was acceptable, the fire marshal will probably put up with it . . . for now.

The right-hand part of the diagram shows the correct - new - method of wiring a tamper switch. The new method shows a separate zone input for the waterflow switch and the tamper switch. With a separate supervisory zone to the panel, the supervisory tamper signal says to the owner "turn the water back on".


The NFPA 72 shows what is needed for several different types of fire alarm systems. Remember, though, that to protect from fire, the NFPA has published hundreds of Codes Books that have to be followed. For instance, in a particular occupancy the NFPA 101 shows what kind of fire alarm system should be used. Other codes published by the NFPA include requirements for manufacturers, testing laboratories, sprinkler systems, fire marshals, elevators, electrical systems, and the list goes on and on.

Many of the requirements that we adhere to are in the NFPA Codes other than what can be seen in the NFPA 72; if some requirement isn't being addressed in NFPA 72, it is probably shown directly or indirectly in another code.

See Is it Even Legal to Show a Trouble for a Closed Valve? for background information on the old style of tamper switch wiring.

Douglas Krantz
Life Safety
This website uses cookies. See Privacy for details.
Make It Work Series of Books by Douglas Krantz
Want Regular Updates on Articles Like These?

No Charge - Unsubscribe Anytime