I've been researching the use of plenum rated cable in floor boxes. The NEC states that a slab in direct contact with the earth is a wet location. My research indicates that the main issue of water entering the conduit is not from direct entry but from condensation. The slab is cooler than surrounding air during humid times of the year and it takes a while, but eventually the conduit fills with condensation. I've heard around here that takes about five years. Plenum rated cable is not water proof. Water proof data cable is not plenum rated. BICSI states that it is not NEC code for the plenum rated cable to be used in slab. My personal interpretation is that article 800 gives a choice as to whether or not to follow chapter 3 methods in installing communication cabling and that if you don't choose to follow chapter 3 methods then there is nothing prohibiting the use of plenum rated cable. And whether or not you choose to use chapter 3 methods, the advisability of using wet rated cable that is not plenum rated is questionable.
BICSI - the communication people who certify but are not a law making body - recommend that a splice box be placed at least 50' from the communication rack and then the wet rated cable (presumably in conduit) be run from that location to under slab. The 50' is not optional - if a splice is made in a cable within 50' of the rack, there is reflection that can make the cable unusable. Therefore if the facility is a small facility, there may not be much way of placing a splice 50' from the rack. So from there I guess everything is in enclosures and in conduit.
It appears to me that the NEC committee needs to get with BICSI and figure out a how to that is both legal and works. Currently it appears that we have a choice - make it legal, or make it work. (Or spend an arm and a leg and have a slim chance of doing both.)
Superior Essex has a below grade communication guide with a picture of the recommended installation. You can Google it - I don't know that I should place the link here.
Comments?
BICSI - the communication people who certify but are not a law making body - recommend that a splice box be placed at least 50' from the communication rack and then the wet rated cable (presumably in conduit) be run from that location to under slab. The 50' is not optional - if a splice is made in a cable within 50' of the rack, there is reflection that can make the cable unusable. Therefore if the facility is a small facility, there may not be much way of placing a splice 50' from the rack. So from there I guess everything is in enclosures and in conduit.
It appears to me that the NEC committee needs to get with BICSI and figure out a how to that is both legal and works. Currently it appears that we have a choice - make it legal, or make it work. (Or spend an arm and a leg and have a slim chance of doing both.)
Superior Essex has a below grade communication guide with a picture of the recommended installation. You can Google it - I don't know that I should place the link here.
Comments?