Separation of Fire Alarm wiring and other wiring in a manhole.

[charlie b]

New area for me, as I am more of a power guy than a low voltage systems guy.

Fire alarm signals from Building #1 pass though underground ductbanks to a manhole, and from there to a central monitoring panel in Building #2. Other cables also pass through the same manhole. These include (possibly) telephone, data, and fiber optic cables. There are plans to demolish Building #2, and relocate the central monitoring panel into recently constructed Building #3. The project will also replace all the fire alarm wiring within each existing building (not the recently constructed one, though), and between each building and the central monitoring panel.

Question 1: Are there any rules within the NEC, NFPA 72, or other related codes that would require me to provide some type of separation, within the manhole, between the new fire alarm wires that I will be calling upon the contractor to install and the other miscellaneous system wires that will remain in the manhole?

Question 2: If the answer is yes, then what do you think about the suggestion that I call for the new fire alarm cables to be run within Seal-tite, as the method of providing the separation.

 

[gadfly56]

New area for me, as I am more of a power guy than a low voltage systems guy.

Fire alarm signals from Building #1 pass though underground ductbanks to a manhole, and from there to a central monitoring panel in Building #2. Other cables also pass through the same manhole. These include (possibly) telephone, data, and fiber optic cables. There are plans to demolish Building #2, and relocate the central monitoring panel into recently constructed Building #3. The project will also replace all the fire alarm wiring within each existing building (not the recently constructed one, though), and between each building and the central monitoring panel.

Question 1: Are there any rules within the NEC, NFPA 72, or other related codes that would require me to provide some type of separation, within the manhole, between the new fire alarm wires that I will be calling upon the contractor to install and the other miscellaneous system wires that will remain in the manhole?

Question 2: If the answer is yes, then what do you think about the suggestion that I call for the new fire alarm cables to be run within Seal-tite, as the method of providing the separation.

IIRC, you must maintain a 2" separation between Class 2/3 wire and cable and Class 1 power/light wire and cable where they are run together. "Together" being a somewhat flexible concept. If they were in a cable tray you could use a barrier to separate them. If Seal-Tite meets the code and specification requirements I'd say go for it. I might prefer EMT as the interval between supports can be larger, but if you're only using the Seal-Tite to provide separation while transitioning from one duct bank to another within the manhole I guess that won't be such a big deal.

Depending on the fire alarm panel make/model, consider looking into fiber optic only connections from building to building. Most manufacturers offer modules to allow fiber optic linking of networkable panels, even as a retrofit. Advantages are water intrusion will be less of an issue and you'll have fewer potential problems with noise on the panel-to-panel connections.

 

[charlie b]

I need to reopen this discussion, as the project is about to be issued at the 50% design level. I think that the only wires and cables passing through the manholes of interest are fire alarm, telephone, intercom, internet, and fiber. I don?t understand the distinctions between Classes 1, 2, and 3. Can anyone tell me which Class(es) apply to the types of wires and cables I will be dealing with? Would you need more information in order to answer that question?

 

[nhfire77]

I need to reopen this discussion, as the project is about to be issued at the 50% design level. I think that the only wires and cables passing through the manholes of interest are fire alarm, telephone, intercom, internet, and fiber. I don?t understand the distinctions between Classes 1, 2, and 3. Can anyone tell me which Class(es) apply to the types of wires and cables I will be dealing with? Would you need more information in order to answer that question?

Class 2,3 circuits are limited to 100VA Class 1 is not. Class 2 is 50 Volts or less class 3
I believe is 150V or less, to account for 70 volt audio, etc.
Unless you have an unusual system, those should all be class 2.

There are some intercom and FA audio circuits that could be class 1, but I'm doubting those would be inter-building.

If there are no lighting or power circuits sharing the man hole you should be fine with 2" seperation, just as a good practice, but not required.

I second what gadfly said about fiber for FA underground. One very small nick on a conductor will all Lightning in eventually. A high resistance ground fault above the panel detection threshold will allow a transient in.

 

[pjholguin]

Read through article 725 for more information about classes 1, 2, & 3 systems.

I need to reopen this discussion, as the project is about to be issued at the 50% design level. I think that the only wires and cables passing through the manholes of interest are fire alarm, telephone, intercom, internet, and fiber. I don?t understand the distinctions between Classes 1, 2, and 3. Can anyone tell me which Class(es) apply to the types of wires and cables I will be dealing with? Would you need more information in order to answer that question?