Comm Grounding System

[mikeybmdb32]

Can anyone help me figure out what the purpose of a telecommunications grounding system is? Since the TMGB is ultimately bonded to the service ground system, I?m not understanding why communications equipment cannot just be bonded directly to the ground at the service entrance as opposed to the TMGB. Also, it seems to me that all that the telecommunications grounding system is only bonded to is the panelboards which feed the communications equipment ? is this correct or does it actually have to bond to the communications equipment itself?

 

[dereckbc]

I think I can help you as I work in the Telecom industry as a PPE. Since you use the term TMGB (Telecommunication Ground Bar) I assume you are referring to BICSI standards?

Typically on a single floor pad construction building it is preferred the TMGB connect to the nearest building ground electrode like the ground ring if possible. However BICSI is not tailored to a communications building built for that purpose. It tailors to a typical business complex where Telecom is a second thought and not the main purpose of the building.

In Telecom or switching offices all the equipment is powered from 48 volts battery plants, or dedicated UPS. In those application a dedicated ground bar is dedicated to the DC plant or UPS as a single point ground system reference. But in a commercial application such as I believe what you are doing is not dedicated to that purpose. So what BICSI is saying is to install a ground bar connected with a dedicated conductor to the AC panel equipment ground bar that feeds power to the communication equipment being served by the TMGB. It is a supplemental ground for passive equipment like a X-Connect or patch panels where no active equipment with a power supply or AC or DC service is needed to power the equipment. It satisfies the NEC requirement for all electrical equipment must be grounded grounded or bonded.

In other words it is just a convenient misc ground bar to bond all the passive equipment racks to a equipment ground that does not have an Equipment Ground Conductor installed. By connecting to the AC panel servicing the equipment it ensures the lowest impedance to clear a fault. Keep in mind since passive equipment rack do not have AC power, the ground is not paired with with phase conductors or a single wire ground and the impedance of single wire grounds will be higher than if paired with phase conductors hence the oversize requirements.

Another way to look at it is the Telecom installers who come in behind you and install equipment make less money than you do and do not have a license or knowledge of electrical systems. It keeps them out of electrical panels and power distribution Keeps us safe and employed.

Hope that helps.

 

[dicklaxt]

They are more than likely looking for a clean ground,,,,,,,,meaning eventually it all gets tied to the same earth but when its isolated before it gets there it's kinda like pouring water uphill,in other words all the bad faults should be dissipated.

Heres a sketch recommended by one of the leading instrument panel vendors,this may be very similar to your needs if not exact.

dick