I hope this email finds you well.
I have a question regarding the voice evacuation system and the best speaker wiring method. I would like to know what the codes and standards like NFPA, BS, EN54, IEC, . . . recommend about when to use the Class A wiring method and the Class B wiring method.
Thank you, S A
It's the AHJ who Requires the Methods
Written in legal-ease, the codes and standards are documents are written so that governments can include them their laws. Much of what is written down says "If you have a fire alarm system, these are the absolute, bottom line requirements". The rules show many added-requirements-above-the-absolute-minimum, but these added requirements are usually specified by the AHJ.
Who is the AHJ?
AHJ stands for Authority Having Jurisdiction. The fire marshal is one AHJ, but there are actually many AHJs. To find out who is an AHJ that we, as fire alarm installers are required to listen to and follow, look up the AHJ in the definitions shown in the beginning of the NFPA 72. Once you have looked up the definition shown at the beginning of the code book, use the number of the code definition and go the back of the book to Appendix A. There you will find a further explanation of what is an AHJ.
Basically, the Authority that has Jurisdiction is the fire marshal, the electrical inspector, the building inspector, the design engineers (if the system isn't designed by the installers), the insurance company representative, even the building owner.
Whether it's going to wind up being a Class A or Class B wiring method for the speakers, whether it's going to be a conventional speaker circuit or addressable speakers, the method of a installing voice evacuation speaker system is first determined by the absolute minimum standards shown in the NFPA. Greater requirements can be indicated by any of the AHJs.
If the different AHJs shown above don't require anything more than the bare minimum shown in the NFPA, you, as an installer, are free to install an upgraded system. This, of course, is providing the upgraded system is listed by a testing laboratory like UL, ULC, CE, FM, etc.
Because there are so many AHJs with their fingers-in-the-pot, so to speak, the recommended method is the method that everyone from the fire marshal to the building owner agrees to.