# Sizing of Telecommunications Equipment Bonding Conductor

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#### ferkfitz

##### Member
An associate noted there is a formula to calculate for Sizing of Telecommunications Equipment Bonding Conductors (TEBC) when bonding multiple Equipment Enclosures (or cabinets/racks) for equipment rooms and/or an Information Technology Equipment Room (ITER) - assuming proper/current terminology. The underlying concept is that BICSI(?) approves using qty-2 bonding conductors (one at each end of a row of cabinets) to bond a series of enclosures in leau of connecting separate TEBCs to each cabinet equipment ground bar. Any ideas/suggestions?

#### dereckbc

##### Moderator
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Re: Sizing of Telecommunications Equipment Bonding Conductor

Just so happens I perform this task. What is it you want to know exactly? I would not use a series method, rather a radial/parallel method. The concept is a isolated SPG with respect to the power source.

There are several organizations who publish Telecom grounding specs such as Telcordia, ATIS, ANSI/IEEE, MCI, Lucent, BICSI, etc for a fee.

There is a formula, but it is much easier to use a table based on the length. But the basic formula is the resistance from the OPGP to the equipment shall be less than .005 ohms.

[ January 29, 2004, 06:11 PM: Message edited by: dereckbc ]

#### ferkfitz

##### Member
Re: Sizing of Telecommunications Equipment Bonding Conductor

My preference would be to use a radial method extending only one unit away. This would mean a single TEBC may connect up to qty-3 enclosures - but it does NOT appear to be recognized. What appears to be recognized is a series of cabinets,
with a TEBC at each end (presumably for equal potential & single fault tolerance), connecting to the Telecom Grnd Busbar (TGB).
I presume the AWG size of the TEBC would be sum the individual current (listed or actual) of each cabinet (possibly use 150%) and use NEC Table_250-122 to determine size. As there would be qty-2 TEBC in use, it should more than compensate for a singular device lightning hit (and/or pwr=>Grnd contact).
Prior BICSI doc 'recommended' #6 AWG to each cabinet.
What do you mean by "isolated SPG"?
I haven't found anything yet in ANSI. Just how may documents does one have to pay for to get a 'practical answer'?

#### dereckbc

##### Moderator
Staff member
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 ]

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