Re: Sizing of Telecommunications Equipment Bonding Conductor
First, each operating company (Bell, ATT, Sprint, MCI, etc) has their own operating practices. They are all derived from Telcordia TR-NWT-000295. All other operating companies who do not have an engineering department or standards adopt BICSI or some other organizations standards which are derived from ANSI/IEEE. They are all about the same, and have nothing to do with the NEC. They far exceed any NEC requirements. They are proprietary documents and unfortunately they charge large sums of money for the documents.
Isolated single point ground means all the equipment racks and power source are isolated from the floor, conduits, and any conductive objects and grounded at a single point only. This prevents any outside fault currents from flowing including lightning.
The size of the conductors has nothing to do with NEC 250.122. They far exceed it. Typically you install a FGB (Frame Ground Bus) in the equipment room. The FGB is sourced to a MGB (Master Ground Bus). From the FGB you install an individual 2/0 for each equipment line-up called a frame aisle ground conductor or supplemental. From each supplemental you connect each equipment rack with a short piece of 6 AWG no longer than 3-feet.
Keep in mind if these equipment racks have AC power rather than DC power, then there are special requirements per NEC and interfacing with it to the isolated ground plane. It gets very tricky, and too involved to explain in this forum.
If you send me your email via PM I can send you so info you might find useful
[ January 29, 2004, 07:45 PM: Message edited by: dereckbc ]