Acerca de los circuitos Clase N de la NFPA 72 Ed 2016

La nueva norma NFPA 72 Ed 2016 contiene una novedosa definición que es la de los circuitos Clase N, asociados a las redes de computación ethernet:

 3.3.67* Device (Cl as s N). A supervised component of a life safety system that communicates with other components of life safety systems and that collects environmental data or performs specific input or output functions necessary to the operation of the life safety system. (SIG-PRO)
 
 A.3.3.67 Device (Cl as s N). Class N devices include components connected to a Class N network that monitor the environment (e.g., smoke, heat, contact closure, manual “in case of fire” pull) and/or provide some output(s) (e.g., dry contact, audible/visual alert/notification, addressable speaker) that are required to provide the real-time functionality necessary for the protection of life and property. In this way, a component connected to the network used for noncritical functions (i.e., maintenance) can be differentiated and excluded from the monitoring for integrity requirements of Class N. Also in this way, transport equipment (e.g., switches, routers, hubs, media converters) and other equipment (e.g., printers, storage devices) can be differentiated from the requirements applied to Class N devices if they do not provide life safety–specific environmental monitoring, inputs, or outputs for the life safety system. This is not to say that this equipment is not important to the overall operation of the system, just that this equipment is not considered a “device” in the context of Class N. Equipment that does not meet the definition of a device cannot be specifically supervised but rather generally supervised as they are part of the supervised pathways that service the Class N devices themselves.

En un articulo de Wayne Moore  http://www.nfpa.org/newsandpublications/nfpa-journal/2015/may-june-2015/features/nfpa-72  se hace referencia a tan interesante cambio, el cual me permito copiar y pegar:

Using Ethernet and network infrastructure
 
Another sea change occurring inside the 2016 edition of the code will allow the controlled use of the Ethernet and other computer networks in a building to interconnect the components of a fire alarm system.
 
Traditionally, the distributed components of a fire alarm system have connected with each other using a two-conductor cable. Such a cable interconnects all of the fire alarm initiating devices and fire alarm notification appliances to a fire alarm control panel. However, with the proliferation and availability of computer networks, we now live in an age where we “connect” to almost every communication device we use through the Ethernet or other computer networks.
 
A look ahead at the 2019 edition of NFPA 72.
 
Fire alarm systems have long used computer-based technology to connect various devices and appliances to the fire alarm system control unit. But fire alarm systems have always used a private, customized network particular to the specific fire alarm system control unit in order to ensure a suitably high level of integrity and to ensure that no other communications on that network would interfere with the operation of the fire alarm system. As the Annex of the code explains, in more technical language: “Ethernet devices are addressable but with an important distinction from device addresses on a traditional signaling line circuit (SLC) multi-drop loop. A device with an Ethernet address is, in most cases, a physical endpoint connected to a dedicated cable and distributed throughout a building using switches and routers. Traditional SLC devices are all wired on the same communication line (in parallel), similar to an old party-line telephone system. By comparison, Ethernet’s network switches direct each data packet to its intended recipient device like our modern phone systems.”
 
The fact remains that rigorous computer networks now exist in many buildings. This has prompted a question to the NFPA 72 Correlating Committee as to why building owners can’t utilize these same networks to connect all of the fire alarm system devices and appliances to a fire alarm control unit. Allowing the use of the existing computer network in a building would greatly reduce wiring costs, proponents argue, and provide greater flexibility for changes and additions that heretofore presented a costly and time-consuming endeavor.
 
Naturally, the Technical Committees had reservations about the use of these networks. By using a shared network, how would the fire alarm system maintain priority if other signal traffic overloaded the capability of the network? How would the fire alarm system monitor the integrity of the network, as it had done with its private network? An informal study conducted by a leading manufacturer that looked at fire alarm system status monitoring via the Ethernet revealed that Ethernet monitoring experiences “down time” or unavailability from 0.75 percent to 1.50 percent of the time. Most of the events that contribute to this down time arise when information technology personnel take other systems down for upgrades, reconfigurations, rerouting of cables, testing, and maintenance. It appeared to the Technical Committees evaluating the use of Ethernet networks that using such a network as a single means of fire alarm system device and appliance interconnection may present reliability issues.
 
In response to these concerns, the Technical Committees have developed a new circuit designation called “Class N.” They have defined this circuit as including two or more pathways that must have their operational capability verified through end-to-end communication. The redundant path intends to compensate for Ethernet wiring that cannot meet all of the fault monitoring requirements that normally apply to traditional wiring methods used for fire alarm circuits. The use of these computer networks as allowed by the code, along with the feedback from designers, authorities having jurisdiction, and installers will certainly make this topic one of ongoing interest.

De acuerdo a este cambio, bajo ciertas condiciones, y con la disponiblidad de la tecnologia, seria probable conectar partes del sistema de deteccion via la red de computadoras de la empresa. Si bien ya existen soluciones para usar la ethernet para fines de monitoreo ( ejemplos: http://resource.boschsecurity.com/documents/Conettix_DX4020_Installation_Manual_enUS_2672298891.pdf    https://www.notifier.com/salesandsupport/documentation/Datasheets/DN_6928.pdf ) estamos hablando de enviar comunicación vital como estatus de detectores o módulos a los paneles, o conectar redes de paneles como una capa de la red existente.

Estas licencias de la norma permitirían “aprovechar” el cableado estructurado de las empresa para minimizar costos en nuevas instalaciones, como también permitirían hacer una integración natural a los sistemas de detección con otras plataformas de inteligencia de edificios.

De igual forma, agregan una necesidad de formación adicional al ingeniero de diseño, que ahora deberá enfrentar la posibilidad de requerir conocimientos de redes de computadora.

De todas maneras, no hay porque hacer criticas más allá de lo técnico y evaluaciones mas estrictas que las de la confiabilidad de los nuevos sistemas comunicados via ethernet, ya que esto forma parte de la evolución tecnológica.

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