Does the NFPA 72 or the NFPA 101 dictate the use of Class A, Class B, or Class X? The guidelines for fire alarm systems shown in the NFPA 72 and the NFPA 101 are the absolute minimum requirements needed to have a system that detects fires and warns people. Anything less than the absolute minimum just doesn't detect all fires, or warn people properly, or both; more than the absolute minimum means that the system has more safeguards and is more reliable.
Usually, it's one of the many AHJs that require more.
The background is that the National Fire Protection Association, Inc. (NFPA) is a non-profit publishing house. Their "Code" publications are a description of what it takes to provide a bare minimum fire protection system. In reality, fire protection and fire alarm systems can be done better than the bare minimum shown in the "Code".
The reason that the NFPA calls the books "Code" is the books are written in a legal language and method that governments can just copy/paste into their legal code, or laws.
When looking up category of occupancy, the NFPA 101 or the International Building Code (IBC) can be used. They show what type of fire alarm system should be used for a specific category of occupancy. (There are several types of fire alarm systems, and each type can have variations.) Remember, the NFPA Code can be thought of as a government's list of laws. It is organized so those enforcing laws can understand them, not so that fire alarm designers, installers, and technicians can readily see the reasons behind the laws.
The NFPA specifies that the fire marshal, the electrical inspector, the insurance representative, and even the building owner can require more than the NFPA requires.
Whereas the NFPA and IBC are, in reality, published guidelines:
- Governments Dictate. One of their legal representatives is the fire marshal; the fire marshal is an authority that has jurisdiction over fire protection.
- Insurance Companies Dictate. They insurance companies have representatives; the insurance representative is an authority that has jurisdiction over fire protection.
- Building Owners Dictate. They own the building, and they own the fire alarm system; the building owner is an authority that has jurisdiction over fire protection.
Many AHJs have authority over fire protection.
Just Who Is the Authority Having Jurisdiction (AHJ)?
Class A, Class B, Class X
The NFPA 72 Code shows seven major classifications for building circuit wiring.
- Class A
- Class B
- Class C
- Class D
- Class E
- Class N
- Class X
NFPA's 7 Classes of Fire Alarm Paths
Absolute Minimum - Class B
- In most places in the "Code", using Class B for the building's circuitry is the absolute minimum. Class B will turn on the trouble light and buzzer when something goes wrong, and that's about it. When the trouble light and buzzer come on, the building owner calls for service. Until the circuit is fixed, some or all of the devices on the circuit will fail to detect fires or warn anyone when there is a fire.
Better - Class A
- When one of the many AHJs require Class A, the biggest extra requirement that they are imposing is the ability for all the devices to still communicate with the panel even if there's a break in the circuit. With Class A, there's a redundant pathway for signals around the break so all the devices are still connected to the panel. When there's a break, the trouble light and buzzer comes on, and then the building owner calls for service. But even before the circuit is fixed, all devices are still connected to the panel; Class A still detects fire and warns people.
Best - Class X
- This is for an addressable Signaling Line Circuit (SLC). When one of the many AHJs require Class X, in addition to the benefits of Class A circuitry, if there's a short on the circuit somewhere, the short is isolated. The trouble light and buzzer come on, and then the building owner calls for service. Even when the wires in the circuit are shorted together, the circuit still works as a Class A circuit.
NFPA versus AHJ
I don't know of any exact wording in the NFPA that dictates specifically that Class A, Class B, or Class X has to be used. I do know, however, that if any of the AHJs specify anything more stringent than what the NFPA specifies, the AHJ's specification (even according to the NFPA) becomes the requirement. If an AHJ specifies that Class A will be used, then Class A is the requirement. If the AHJ specifies that Class X will be used, then Class X is the requirement.
If the fire marshal is requiring something, just remember - the NFPA 72 is a published book; the fire marshal is a representative of the government.