Douglas Krantz - Technical Writer - Describing How It Works

Are they Telephone Wires or Data Wires?

By Douglas Krantz | Descriptions

Are they Telephone Wires or Data Wires?

Are they Telephone Wires or Data Wires?

Greetings Douglas,

A NAC circuit is a Notification Appliance Circuit and a SLC is a Signaling Line Circuit. These are standard classifications and generally accepted by everyone who is professionally working with fire alarm systems. But there is one wire-circuit that I am trying to find how to properly identify it, on shop drawings and to the AHJ.

This may sound rather stupid, but it's the telephone lines that run between the fire alarm control panels built in telephone jacks and the cellular transmitter unit. Are these called telephone lines or are they called data communication lines? Just how should they be called and be in unison with NFPA 72?

Thank You, TH

Short Answer

If there's a dial-tone, and the panel dials to get out, the wires are technically defined as a telephone line, or POTS (Plain Old Telephone System).

Long Answer

This sounds weird, but the National Fire Protection Association, Inc. (NFPA, a publishing house) has for years been extricating themselves from having to define wires for fire alarm systems. Instead of defining wires for fire alarm systems, they are defining pathways.

Wires carry voice and data, fiber optics carry data, wireless (RF or radio frequency signals) carries voice, video, and data. The NFPA can't keep up with all the changes, so they are letting the manufacturers design their own systems. Once designed, if the testing laboratories, like UL, ULC, FM, CE, CCC, etc., place the designed equipment on their list of devices that can be used for fire alarm systems (Listed for Use), then the equipment can be used for fire alarm systems.

The wiring is part of the Listing. In the installation manuals and installation sheets that come with fire alarm systems, the kind of wiring is shown. Any other type of wiring knocks the system out of being listed (the equipment is no longer Listed for Use), so use the wiring shown in the manufacturer's installation manuals.

POTS System - Telephone Wires

The POTS telephone system was originally a complete pathway between one person and another. A person calling from the "Parkway" neighborhood could dial up someone else receiving the call in the "Taylor" neighborhood.

The person calling used two copper wires to connect with the downtown central office of the telephone company. Using dialing relays, the central office would electrically connect the caller's two copper wires to the copper wires connected to the receiving person's telephone.

This was a DC (Direct Current) pathway connection, and the copper wires between the central office and the calling person's or the receiving person's telephones were telephone lines.

The signals carried on the telephone lines were analog - not digital - because the telephone system is an analog system.

Remember, people's voices on the POTS system are analog. Computers sending digital information over the POTS system have their digital information converted to analog. Computers receiving digital information from over the POTS system have the analog information on the telephone lines converted to digital information.

You just can't change the two wire analog POTS system to a digital system, and at the same time, keep it a POTS system. If there's a dial tone, it's a POTS system.

NFPA's Classification of Pathways - Types of Supervision


NFPA's 7 Classes of Fire Alarm Paths

The copper wires between the fire alarm control panel and the cellular transmitter unit are part of the pathway between the fire alarm control panel and the off-site computer at the central station.

The whole end-to-end communication system, including the copper wires and the cellular communication system, with the fire panel at one end the central station's computer at the other end, is a Class C fire alarm communication pathway.

If, after sending one of its regular test signals, the fire alarm panel doesn't receive a confirmation signal back from the off-site central station, the fire alarm panel thinks that something's wrong, and turns on its trouble light and buzzer.

If the off-site central station doesn't receive one of the regular test signals from the fire alarm control panel, the central station computer thinks something's wrong, and requires that someone call to report the trouble to the building's management.

Wires and Class C

To answer your question, the copper wires are telephone wires. The wires are part of a Class C pathway.

Also, if there is a name for the wiring shown in the installation manual, that is the name that should be used for the shop drawings and for the AHJ, because that name is the "Listed for Use" name.

Douglas Krantz
Life Safety
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