The Advantages of Class A Fire Alarm Systems

General Difference

• There are generally two main classes of fire alarm systems, A and B. A class A fire alarm system circuit is different from a class B in its ability to operate when the circuit's integrity is compromised. A class B system will not function fully if there is damage to any part of the circuit, whereas a Class A can continue to operate. This advantage may save a life by alerting an individual to a fire in spite of a problem in the alarm circuitry.

Problem With Class B

• The Class B is a more common type of fire alarm system. In it, conductors originate at the alarm control panel and support the peripheral devices. If the circuit has a problem, such as a short in the wire, the peripheral alarm section is not able to communicate with the control unit. If there is damage to the circuit, the alarm at the control will still sound, but it may not be able to alert individuals in the areas where peripheral devices are located.

Class A Superiority

• Class A is superior to class B in its survivability. Class A is similar to B in that the origination is still the control panel and that it, too, supports peripheral devices. The difference in the two systems is found in the circuit formation. The A classification requires outgoing and return conductors, which creates a loop circuit. The A circuit returns to the control panel after the last peripheral device is contacted. Thus, if a circuit is damaged, the device ahead of the problem area can still communicate with the control panel, as in Class B. However, downstream devices are also able to transmit on the returning conductors, unlike Class B.

Class A Spacing

• The class A circuit is ensured even more survivability due to NFPA 72's safety code. This requires that Class A circuits be installed in conduits that are physically separate from each other. The code suggests a minimum spacing of 4 feet between conductors if routed horizontally. The recommendation for spacing of vertically routed conductors is 1 foot.