From the June, 2013 Issue of Cabling Installation & Maintenance Magazine
We received multiple pieces of feedback after publishing the article entitled "6 common mistakes to avoid in telecom technology grounding" (February 2013, page 9), authored by Mo Masghati, director of new product development with ITW Linx. Additionally, the article was the subject of discussion in some social-media boards.
As is often the case when the subject of grounding comes up, the correspondence included significant technical detail. Space limitations prohibit us from providing the feedback in its entirety here, but the following pages reflect the tenor of the commentary and, to the extent possible, detail as well.
Reader William Bush, an EMC design engineer and Lightning Protection Institute-certified designer/inspector, provided the following.
This type of article is a marketing piece, placed with good intentions but severely lacking in technical competence. To be fair, this situation has been happening in magazines since the days of early divestiture. At a minimum, critical statements and facts should be accompanied by a citation to the resource utilized. There is also responsibility attributable to the publisher for ensuring the article will be reasonably competent. Just publishing an article that "appeals to consumer concerns" does not ensure its accuracy or applicability. Just mention lightning and grounding and most people conjure up "magical practices" are somehow necessary.
The opening paragraph is misleading. The importance of grounding is not overlooked as the applicable local code (typically the National Electrical Code) requires adequate grounding of the power system(s), bonding to any lightning protection system (LPS) employed, and intersystem bonding (direct or by SPD [surge-protection device]) to any communication lines entering the building. Further, ATIS 0600318, TIA 607-A, TIA 607-B and BICSI TDMM echo these same requirements.
Application guidelines for SPDs (both communications and AC power) are adequately provided for by IEEE SPDC (Surge Protection Devices Committee). Concentrating on only one type of port (comms) will not prevent upset or damage unless the remaining ports are also addressed in concert. This usually means a multi-service (AC, paired comms, coax comms, etc.) and multiport (paired comms, Ethernet, coax, etc.) SPD (a.k.a. surge reference equalizer) is required at the unit equipment. Also, at the service provider entrance location proper bonding and grounding of exposed (lightning and power cross) conductors is required in accordance with NEC requirements and the recommendation of ATIS 0600318. This involves direct grounding of metal cable sheathing and coax cable shields plus SPDs for the cable pairs and coax center conductor. Further, intersystem bonding of the grounding electrodes for the AC power and comms services is also required by the NEC and ATIS 0600318. The NEC-required one common grounding electrode system for a premises is thus maintained. A useful one-document treatment is provided in IEEE Std. 1100-2005 Recommendations for Powering and Grounding Electronic Equipment.
Mr. Bush then addressed several of the specific "common mistakes" addressed in Mr. Masghati's article. The first such mistake was dubbed "Not understanding impedance guidelines." Mr. Bush offered the following.
I am not aware of any FCC requirement for a 1 Ohm or less ground. The effectiveness of the SPD depends upon its time to operate, its rated clamping voltage, and its remnant voltage passed on to the protected equipment. The SPD's clamping voltage and the transient voltage buildup in its connecting lead (to its ground reference location—such as the telecommunications main grounding busbar) determines the impinging total voltage surge upon the device. The intersystem bonding of the common grounding electrode system ensures the SPD's clamping voltage is the only overvoltage as referenced to local earth grounding medium—or whatever serves as the local grounding medium (such as an airplane frame). There is a new treatment on this item in IEEE C62.72 draft 2012 that confirms the above statement.
However, the overvoltage of the local grounding medium (such as earth) can be significant relative to remote earth ground. This overvoltage is termed "ground potential rise—GPR" and can cause SPDs to "backfire" and use the protected circuits to access a remote ground. In this sense, having the local earth ground value as close as practical to remote earth ground value has some limited benefit where metallic links connect across campuses, etc. But even in this case, the metallic links at the other campus locations should have direct grounding and SPDs also applied, in accordance to the previously mentioned standards. GPR is considered a special electrical protection application for electrical substations and communications towers and is primarily covered in IEEE 367-2012 and ATIS 0600334.
In response to these and other comments supplied by Mr. Bush, the article's author, Mr. Masghati, responded.
We are delighted to see the article has sparked conversation and dialogue on this very important topic. We thank Mr. Bush for his interest and insights.
There seems to have been some misunderstanding about the intention and focus of the article. Our article never implied that there are not specific grounding codes or regulations. In fact, we commonly cite these codes. Our point is that these codes are sometimes overlooked or misunderstood by installers. A vast majority of the calls we receive regarding damaged telecom technology can be traced to a ground- ing error of some type. Hence our desire to put together a "tips" piece to provide insights into commonly made mistakes. Our perspective was more "in the trenches" than "on the books."
As the title of the article indicates, we focused specifically on mistakes in grounding telecom technology. This technology is by nature extremely sensitive as it is low voltage and transmits data at high speeds. Many of Mr. Bush's points seem to refer to general electrical safety for buildings and individuals.
The grounding requirements for protecting sensitive telecom equipment somewhat differ from general cabling grounding requirements. For example, Mr. Bush's comments on "Grounding Mistake 1" make a lot of sense when viewed in the context of grounding for residential purposes. However, for telecom equipment (the focus of the article), the sensitivity of complicated technology means that high-level data management facilities require greater protection. We recommend following FCC recommendations (not requirements) of ensuring 1 Ohm or less for these applications.
We're not pretending this point/counterpoint closes the book on this type of conversation. In our experience any conversation related to grounding can and often does take on a life of its own. Please email your feedback to our editor, [email protected]. We will continue to cover this and other topics you deem to be worthwhile and valuable. –Ed. ::
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