desnov74,
Don't know if you already received an answer to your questions by other means. I just saw this post today so sorry it's late. I looked through NFPA 72. It doesn't address overvoltage devices (generally points you to the NEC). In Article 760.32 of the NEC, I was directed to Parts II, III, or IV or Article 800. Here's what I found in Part III of Article 800:
800.90 Protective Devices.
(A) Application. A listed primary protector shall be provided on each circuit run partly or entirely in aerial wire or aerial cable not confined within a block. Also, a listed primary protector shall be provided on each circuit, aerial or underground, located within the block containing the building served so as to be exposed to accidental contact with electric light or power conductors operating at over 300 volts to ground. In addition, where there exists a lightning exposure, each interbuilding circuit on a premises shall be protected by a listed primary protector at each end of the interbuilding circuit. Installation of primary protectors shall also comply with 110.3(B).
FPN No. 1: On a circuit not exposed to accidental contact with power conductors, providing a listed primary protector in accordance with this article helps protect against other hazards, such as lightning and above-normal voltages induced by fault currents on power circuits in proximity to the communications circuit.
FPN No. 2: Interbuilding circuits are considered to have a lightning exposure unless one or more of the following conditions exist:
(1) Circuits in large metropolitan areas where buildings are close together and sufficiently high to intercept lightning.
(2) Interbuilding cable runs of 42 m (140 ft) or less, directly buried or in underground conduit, where a continuous metallic cable shield or a continuous metallic conduit containing the cable is connected to each building grounding electrode system.
(3) Areas having an average of five or fewer thunderstorm days per year and earth resistivity of less than 100 ohm-meters. Such areas are found along the Pacific coast.
In my interpretation, the NEC tells us to install overvoltage device if the fire alarm (communications) circuits between buildings are run in proximity to light/electric circuits of 300 volts or more; or where there is lightning exposure (see FPNs above). If your circuit is underground, you should be okay not to use an overvoltage device as long as the circuit is protected by properly grounded metallic conduit and the circuit is 140 ft or less.
As a recommendation...you may want to consider contacting the panel manufacturer and asking them if they believe you need the overvoltage device given your particular design/installation and building configuration(s)/heights, etc.
Hope this helps.
If anyone out there has a different opinion/interpretation, please share. I'm still learning too.
Shawn Lee
