I Was Wrong… Or Was I? Part 2
The NEC and the NESC Codes on Bonding and Grounding
I received an email from Percy E. Pool, P.E. (retired protection engineer) commenting on my December 2011 column, Are You Really Ready for The Triple Play?, Percy had concerns on the validity of my statements on bonding and grounding at the Network Interface. Please see last month’s column, February 2012, for the first part of my response. Following is Part Two.
In an endeavor to answer Mr. Poole’s comments, I consulted with expert, Bob Olgeirson, manager of Telecom Training & Safety Inc., a non-profit organization providing technical and safety information and training to the employees of 14 telecom companies in and around North Dakota. Bob is a former instructor/adjunct professor of electronics, with 37 years in telecommunications/electronics; 17 of those years he spent in training, and 20 years working and supervising communications maintenance. Bob’s NEC and NESC research on bonding and grounding is follows:
The NEC and NESC are embedded (whole or in part) in state codes and are enforced through legal statues. They also represent standards of performance for liability purposes. From a telecom standpoint, the NEC covers the customer premises and the NESC covers plant equipment owned or exclusively maintained by the telecom utility.
The point where these 2 codes come together is the NID, including grounding of the NID. Usually the codes agree, but this year because they are published at different times they are not identical. Following are brief descriptions as they apply to the 2 codes.
• The National Electrical Code (NEC) is published by the National Fire Protection Association (NFPA) and is applicable to customer premises. It does not apply to “communications equipment under the exclusive control of communications utilities located outdoors or in building spaces used exclusively for such installations.” NEC 2011
• The National Electrical Safety Code (NESC) is published by the Institute of Electronics and Electrical Engineers (IEEE) and is applicable to the power and telecommunications industries. It covers transmission and distribution of communication signals and data through equipment installed and maintained under the exclusive control of utilities or their authorized representatives.
• Referenced NEC Paragraphs (underlines added):
NEC 2011, 250.53 Grounding Electrode System Installation
(A) Rod, Pipe, and Plate Electrodes. Rod, pipe and plate electrodes shall meet the requirements of 250.53 (A)(1) through (3).
(1) Below Permanent Moisture level. If practicable, rod, pipe and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from non-conductive coatings such as paint or enamel.
(2) Supplemental Electrode Required. A single rod, pipe, or plate electrode shall be supplemented by and additional electrode of a type specified in 250. 52(A)(2) through (A)(8). The supplemental electrode shall be permitted to be bonded to one of the following:
(1) Rod, pipe, or plate electrode
(2) Grounding electrode conductor
(3) Grounded service conductor
Exception: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required.
(3) Supplemental Electrode. If multiple rod, pipe or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft.) apart.
Previous NEC 25 ohm requirement
NEC 2008 250.56 Resistance of Rod, Pipe, and Plate Electrodes.
A single electrode consisting of a rod, pipe, or plate that does not have a resistance to ground of 25 ohms or less shall be augmented by one additional electrode of any of the types specified by 250.52(A)(4) through (A)(8). Where multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft.) apart.
NEC 2011, 800.156 Dwelling Unit Communications Outlet.
For new construction, a minimum of one communications outlet shall be installed within the dwelling and cabled to the service provider demarcation point.
NEC 2011, 250.94 Bonding for Other Systems.
An intersystem bonding termination for connecting intersystem bonding and conductors required for other systems shall be provided external to enclosures at the service equipment or metering equipment enclosure and at the disconnecting means for any additional buildings or structures. The intersystem bonding termination shall comply with the following:
(1) Be accessible for connection and inspection.
(2) Consist of a set of off terminals with the capacity for connection of not less than three intersystem bonding conductors.
(3) Not interfere with opening the enclosure for a service, building or structure disconnecting means, or metering equipment.
NEC 2011, 800.100 Cable and Primary Protector Bonding and Grounding.
The primary protector and the metallic member(s) cable sheath shall be bonded or grounded as specified in 800.100(A) through (D).
(A) Bonding Conductor or Grounding Electrode Conductor.
(1) Insulation. The bonding conductor or grounding electrode conductor shall be insulated and shall be listed and shall be permitted to be insulated, covered or bare.
(2) Material. The bonding conductor or grounding electrode conductor shall be copper or other corrosion-resistant conductive material, stranded or solid.
(3) Size. The bonding conductor or grounding electrode conductor shall not be smaller than 14 AWG. It shall have a current-carrying capacity not less than the grounded metallic sheath member(s) and of the protected conductor(s) of the communications cable. The bonding conductor shall not be required to exceed 6 AWG.
(4) Length. The primary protector bonding conductor or grounding electrode conductor shall be as short as practicable. In one- and two-family dwellings, the primary protector bonding conductor grounding electrode conductor shall be as short as practicable, not to exceed 6.0 m (20 ft.) in length.
(5) Run in straight line. The bonding conductor or grounding electrode conductor shall be run in as straight a line as practicable.
(6) Physical protection. Bonding conductor or grounding electrode conductors shall be protected where exposed to physical damage….
NEC 2011, 250.64 Grounding Electrode Conductor Installation.
Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F).
(A) Aluminum or Copper-Clad Aluminum Conductors. Bare aluminum or copper-clad aluminum electrode conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum electrode conductors shall not be terminated within 450 mm (18 in.) of the earth.
(B) Securing and Protection Against Physical Damage. Where exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried. Grounding electrode conductors shall be permitted to be installed on or through framing members. A 4 AWG or larger copper or aluminum grounding electrode conductor shall be protected if exposed to physical damage. A 6 AWG grounding electrode conductor that is free from exposure to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection if it is securely fastened to the construction; otherwise, it shall be protected in rigid metal conduit (RMC), intermediate metal conduit, (IMC) rigid polyvinyl conduit (PVC), reinforced thermosetting resin conduit (RTRC), electrical metallic tubing (EMT), or cable armor. Grounding electrode conductors smaller than 6 AWG shall be protected in RMC, IMC, PVC, RTRC, EMT, or cable armor.
The above codes would drive a Philadelphia lawyer to drink, and they just cover the safety aspect. From a technical aspect, insufficient and improper bonding and grounding have an adverse affect on bandwidth. If you have thoughts on this or anything that’s interesting or troublesome within your job, please let me know: firstname.lastname@example.org or 831.818.3930.