XFMR Electrical GEC at Telecommunications Ground Bar (Previous Question/New Post)

[msimms]

I've raised this question before, but didn't seem to generate a lot of notice so I'll try and ask it again based on new information found. I've attached a one-line to provide a visual of the installation.

A contractor has taken a GEC from each of two (2) dry-type transformers both located in a telecommunications room, to a telecommunications ground bar (TMGB). Each dry type XFMR (480-208/120) feeds a power panel serving telecom loads; each power panel per TIA-607-A is required to have a bonding jumper to the TMGB. The same TMGB is also required (per the same TIA standard) to bond to building steel and in my interpretation is to be used for telecommunications equipment bonding only. The TMGB is then is then bonded to a Main Ground Bar via 4/0AWG located in another room, with the MGB designed as the common connection point for each grounding electrode defined under 250.52, which is allowed per 250.30(A)(6), 250.64(D)(1)(3), and 250.66(F)(3) (example references located). The MGB serves as part of a common connection point for building grounding electrodes to meet 250.50 regarding the grounding electrode system. Three questions:
(1) The TMGB is already properly bonded to the MGB as mentioned. Since the TMGB also bonds to building steel, and even though it’s considered only for telecommunications, is there a chance that the GEC from each transformer is allowed to go to that TMGB even if its an intermix of electrical and telecom grounds?
(2) Are there concerns with the required bonding jumper also terminating at the same TMGB, with any potential ground loops being created with the GEC also terminating at the same location?
(3) Would electrical noise be a concern given the transformer’s direct connection the TMGB, being imposed on the telecom equipment?

 

[electrofelon]

I dont have the wording in front of me now, but i do not believe that the TMGB is an allowed location to land the GEC for an SDS. Although it ultimately goes to where you need to be, it is essentially being spliced on the TMGB.

I doubt there will be any problems with ground loops or "noise"

 

[ron]

Although TIA-607-A is a great reference, there are plenty of other grounding and bonding references that differ slightly regarding what you describe such as IEEE Std 1100 (Recommended Practice for Powering and Grounding Electronic Equipment). Since none of them are adopted codes, which takes precedence is often contractual or per manufacturer's instructions.

I didn't have enough time to review the conductor sizes you mentioned but in general, often NEC 250.30(A)(6)(b)(2) allows for a common grounding electrode conductor busbar to be used for multiple SDS and doesn't prohibit use of that common grounding electrode conductor for other non-required bonding such as telecom.

 

[electrofelon]

Although TIA-607-A is a great reference, there are plenty of other grounding and bond references that differ slightly regarding what you describe such as IEEE Std 1100 (Recommended Practice for Powering and Grounding Electronic Equipment). Since none of them are adopted codes, which takes precedence is often contractual or per manufacturer's instructions.

I didn't have enough time to review the conductor sizes you mentioned but in general, often NEC 250.30(A)(6)(b)(2) allows for a common grounding electrode conductor busbar to be used for multiple SDS and doesn't prohibit use of that common grounding electrode conductor for other non-required bonding such as telecom.

Ok I agree. The TMGB, for NEC SDS purposes, can be considered the allowed SDS grounding busbar, as long as it meets the required dimensions. I never noticed the GEC busbar provision was allowed for SDS's.

 

[msimms]

So the TIA-607-A is the contractual reference alongside 2014 NEC in my case. I contacted BICSI as well who like myself desired only telecom bonds back at the TMGB, before using the telecom bonding conductor to bond to the main ground bar. None of the documentation they have includes bonding the XFMR GEC to the telecom bar. For this research I've been doing, I've gone through the NEC and IEEE references including 1100 amongst others; the most that I'm able to confirm is the requirement that telecommunications system is supposed to at least bond back to the electrical system ground to avoid differences in voltage conditions between grounded metal objects during faults and/or lightning. Nothing shows an allowance of mixed electrical (in this instance XFMR GECs) and telecom connections at the same bar, however nothing clearly states that it's not allowed either; hence the question. The TMGB in this instance meets the 1/4"x 2" requirement per the NEC, but is not directly connected to building steel (yet).

So based on the responses here:
1) Hypothetically, if the XFMR GECs remained at the TMGB, is it interpreted that if the TMGB is only bonded to the MGB (which is considered a common point for grounding electrode connections) that this still satisfies the NEC? That the TMGB via its connection to MGB in our case serves as an extension of the grounding electrode system, hence allowing essentially a busbar to busbar to grounding electrode connection?

2) Also, reading of 250.30(A)(4) for SDS indicates the location best suited is either metal water pipe or structural metal; only use others per 250.52(A) if these are not available based on Exception #1. Is this an order of precedence? Why the requirement to send the GEC to only one of these two electrodes first?

 

[infinity]

Going from memory here, aren't you required to use the building steel for the transformer grounding electrode and not solely a common grounding electrode?

 

[jaggedben]

Regarding your question 2 in your last post, this section was substantially revised in the 2017 NEC to simply say that the SDS must be grounded to the building grounding electrode system. So no, I don't think the order or precedence is of importance. Or maybe it was thought so at one time but opinions have changed.

 

[jaggedben]

Going from memory here, aren't you required to use the building steel for the transformer grounding electrode and not solely a common grounding electrode?

No. Not by the NEC anyway. For one thing, the building might not have structural steel, and conceivably might not even have water service either. In 2014 this is covered by the exception and in 2017 you simply use the building GES.

Actually, in the 2017 NEC I've lost track of which section even permits you to ground an SDS to building steel.

 

[jaggedben]

Actually, in the 2017 NEC I've lost track of which section even permits you to ground an SDS to building steel.

Nevermind, that would be 250.68(C)(2). Note there are some specific requirements to qualify.

 

[infinity]

Doesn't 250.30(A)(4) clearly indicate which electrodes you must use if they're available?

250.30(A)(4) Grounding Electrode. The grounding electrode shall
be as near as practicable to, and preferably in the same area
as, the grounding electrode conductor connection to the
system. The grounding electrode shall be the nearest of one
of the following:
(1) Metal water pipe grounding electrode as specified in
250.52(A)(1)
(2) Structural metal grounding electrode as specified in
250.52(A)(2)

 

[jaggedben]

...
(2) Are there concerns with the required bonding jumper also terminating at the same TMGB, with any potential ground loops being created with the GEC also terminating at the same location?
(3) Would electrical noise be a concern given the transformer’s direct connection the TMGB, being imposed on the telecom equipment?

A ground loop would be created if the telcom equipment has an internal grounding connection between the power source EGC and the grounding connection that goes to the TMGB. This is true regardless of where the transformer is grounded, since both connections would ultimately be bonded to the MGB. If the transformers are grounded to the TMGB, the ground loop will be shorter, which to my knowledge would probably be better (smaller antenna loop). I don't know whether any of this is a real concern at all. I think it would really depend on the application and the particular equipment.

 

[jaggedben]

Doesn't 250.30(A)(4) clearly indicate which electrodes you must use if they're available?

If you're still on the 2014 NEC, yes. If you're on the 2017 NEC all that language was replaced, and it simply says to use the building grounding electrode system.

 

[jaggedben]

The other NEC sections that might be relevant to this thread are the intersystem bonding sections, 250.94 and various identical .100(B)(2) sections in 770, 800, and so on. In the 2017 NEC 250.94(B) seems to allow for communication system connections to busbars with other connections. 2014 NEC doesn't have that section.

 

[infinity]

If you're still on the 2014 NEC, yes. If you're on the 2017 NEC all that language was replaced, and it simply says to use the building grounding electrode system.

Yeah we're still on the 2014. I like the 2017 better.

 

[msimms]

Thanks everyone; again as a note, we're under the 2014 NEC, but that doesn't mean I won't at least reference 2017 for information.
[MENTION=129901]jaggedben[/MENTION] - we don't have intersystem bonding in place here, but I did take into account 800.100(B)(2) regarding grounding means requirements. Again, a lot of this has more to do with the line of demarcation between electrical system grounding and telecom system grounding. I now see the updated (2017) NEC 250.94(B) statement "for communication systems in addition to other connections" that may be interpreted to allow potential electrical and telecom on the same bar, but its still somewhat ambiguous in my mind. What I also referred to was Informational Figure 800(a) which aligns with our installation; all of our electrodes are bonded together back at the MGB and our connection between the TMGB and MGB (via Telecom Bonding Conductor) is meeting this installation method IMO (i.e. - no separate comm grounding electrode). The closest form of electrical and telecom bonding otherwise is the required equipment bonding jumper (ACEG) to the TMGB from the panelboard per TIA-607-A, however again nothing from a transformer much less a GEC.

So the 2017 NEC updated the allowed methods of connection to the GES, whereas 2014 doesn't directly allow it without a first set of if-thens. Assuming the GES is interconnected as we have it here, if the TMGB were not bonded to building steel (again hypothetically), would it be considered connected to the GES if its only bonded to the MGB and not directly to any specific electrode? Again, per 250.64(C), there are continuation requirements for the GEC, except if the conditions are in place per 250.30(A)(5), (A)(6), 250.30(B)(1), and 250.68(C). In our case again, we go from TMGB to MGB to electrode.

Since this blends into the TIA-607-A requirements (and again, I'm still reviewing IEEE 1100 and 142), anyone who works in the telecom installation world have an opinion about electrical XFMR GEC bonded to the same point as the telecom (ITE) bonds? Any reference-able documentation?

 

[infinity]

Since your under the 2014 you are required to do what's outlined in post #10. That means that your building steel must be used as the grounding electrode for the transformer.