Grounding and Bonding of Communications Systems


Comments, Questions and Answers

1.       What is the purpose of grounding and bonding subscriber communication services at the customer premises?

A)        The purpose of grounding and bonding communications systems, as defined in NEC Article 90.1, is to safeguard persons and property from electrical hazards. NEC Articles 250 and 820 describe the specific protection requirements for each type of facility.

2.          Is a ground rod appropriate for grounding telecommunications services at the premises? May I leave these grounds in place and consider my system to be in compliance with the Code?

A)        Generally yes, NEC Articles 800, 810, 820, and 830 permit the use of ground(ing) rods. However, Article 820.100(D) specifies that each ground rod must be bonded to the building grounding electrode system with a No. 6 AWG copper wire using a separate clamp on the rod for attachment of the bonding conductor.

 3.        Must I ground a coaxial feeder cable if after grounding and bonding it at the entrance to an apartment building the cable exits the building to serve another on the same property?

A)        No, NEC Article 820 specifies that feeder cables that run aerially and pass under power conductors must be grounded at the entrance to the next building. 

4.         What are considered approved grounds?

A)        See NEC Articles 800.100, 820.100 and/or 830.100 depending on the type of communication system.

 5.        DPS staff uses clamp-on ammeters to check for sheath current on coaxial cables.  What is the purpose? May I do the same to verify a ground?

A)        Identifying current flow on the coaxial cable is one process used to verify the ground connection’s electrical continuity.

            Where a conventional CATV service coaxial cable is grounded and bonded to a building grounding electrode system, a part of which is the electrical service ground, a current will flow in the coaxial cable sheath if power is being used in the dwelling and if the power load in the dwelling is not balanced.

            In thousands of measurements, our staff has found sheath currents above 3 amperes in some instances. The average has been approximately 0.25 amperes. Low readings are in the area of 0.1 amperes while high reading approaches 0.7 to 0.8 amperes.

             Ohm's Law explains why some coaxial cable sheath currents are so low. The coaxial cable sheath resistance is in parallel with the resistance of the neutral conductor. Current flow in each conductor will be inversely proportional to the resistance of each. The resistance of RG59/u sheath is 100 to 150 times that of a typical neutral conductor in residential service and many times greater than that of a neutral conductor in multiple dwelling service. Therefore, the small currents measured are to be expected.

            DPS staff believes that where there is an electrical load on electrical ground, the presence of current in the coaxial cable sheath indicates that a connection of some kind exists between the CATV coaxial and the electrical service. We do not believe however, that current measurements can or should be substituted for a visual inspection of the installed grounding and bonding connections since current alone does not indicate whether the connection is proper or the ground conductor is adequately sized.

            DPS inspectors use clamp on ammeters from a variety of manufacturers for sheath current measurement. The prime concern in obtaining a meter for this purpose is to choose one with a low range full-scale deflection of not more than 1.5 amperes. Higher ranges are not useful.

 6        What should I do when a subscriber will not provide me with access to their basement to check the ground and bond?

A)       It is necessary to attempt to gain access to the house. If denied, a letter explaining the reason for the inspection should be sent to the subscriber. The letter should indicate that your company is required to inspect the service installation. You should include the Commission address (Three Empire State Plaza Albany, NY 12223-1350)and our toll-free telephone number, (800-342-3377), in any letter to subscribers regarding grounding. The letter may request that the subscriber contact the company within a reasonable time (ten days to two weeks) to make an appointment for the inspection. If the subscriber does not make an appointment, the service provider should notify the subscriber that the service may be suspended.

 7        I provide service to a multi-family dwelling. No tenant has access to the basement. The landlord does not live in the building.  How do I gain access to inspect the grounding and bonding?

A)        New York State Public Service Law, Article 11, Section 228 prohibits a landlord from interfering with the provision of cable television service to his tenants. Denial of access may prevent you from providing safe, adequate and reliable service as is required by New York State Public Service Law, Article 11, Section 224. If you are unable to access a basement to inspect facilities you may serve a notice on the landlord, citing Section 228, requesting access to the building. If you fail to gain access, the drop cable(s) must be disconnected. The provisions of Section 228 gives cable television companies certain legal rights that you may wish to explore with your attorney.

8.         For convenience, I want to install separate service cables for each apartment in a multiple dwelling unit. I bring all drops to a common point on the building; must I run separate ground wires from each to a grounding electrode?

A)        No, ground blocks installed in each drop may be connected together using a single grounding conductor run unspliced to a grounding electrode, provided the grounding conductor is of sufficient capacity to effectively ground the combined drops.

            Alternatively, you may run separate No. 14 AWG grounding conductors from the individual ground blocks to a No.10 AWG or larger grounding conductor that is attached to the building grounding electrode system. The individual No.14 AWG conductors may be attached to the No.10 AWG conductor with split-bolts of appropriate size. This configuration is called a "tapped ground." It is not considered to be a spliced ground.

B)        It may be more appropriate to install a splitter (or splitters) in a box on the house. However, both the box(if metal) and splitters must be bonded together and grounded to the building grounding electrode system.

 9.       Is there a maximum length for a grounding conductor in a house?

A)       Yes, NEC Article 820.100(4) limits the length of a ground conductor to 20 feet in one and two family dwelling units. The NEC also calls for the shortest, straightest, and most direct route (uncoiled); avoiding 90 degree bends for the grounding conductor routed to the nearest point on the building electrode system. The Code also requires the coaxial cable shield to be grounded as close to the building entry point as practical.

 10.     What about the length of a grounding conductor in a Multi Dwelling Unit (MDU)?

A)       NEC Article 820.100(4) recognizes that the maximum length of 20 feet for single family installations may not be practical for some MDU’s installations. However, the NEC encourages keeping ground conductor lengths to a minimum recognizing that: “Similar grounding conductor length limitations applied at apartment buildings and commercial buildings will help to reduce voltages that may be developed between the building’s power and communications systems during lightning events.”

 11.     Interior electrical wiring is generally two-wire with a ground. The wall outlet cover plate is secured by a metal screw. The NEC requires that exposed metal subject to being energized be grounded. May I install a ground block on the rear of the TV set or converter and make a grounding connection to the grounded metal screw on the duplex outlet?

A)       No, the grounding conductor should be connected in accordance with NEC Article 820.100(B) (1),(B) (2), or(B) (3).

 12.     I want to install a service cable in a residence where the siding is all aluminum. May I ground the drop to the siding?

A)        No, see NEC Article 820.100(6)(B)Electrode. Although the Code requires that aluminum siding be grounded, that is not always the case. Thus, that would not be considered an approved ground. Likewise, attaching your grounding conductor to that of the siding ground is not an approved method.

 13.     There is a metal conduit containing the service entrance cable installed between the load side of the electric meter and the customer's electrical distribution panel. May I connect a grounding conductor to the conduit?

A)      Yes, see NEC Article 820.100(6)(B)Electrode, for the type of telecommunications service you are installing. The NEC requires that the metal conduit be effectively grounded when installed by the customer's electrician. It is, therefore, part of the building grounding electrode system. Paint or rust should be removed before attaching the ground clamp.

 14.    I have found many service cables in place that no longer serve customers due to subscriber churn. Is it necessary to ground and bond those inactive cables?

A)     Please refer to FCC rules 76.802 (disposition of cable house wiring) and 76.804 (disposition of home run wiring). Customers have a right to acquire the cable, splitters, etc. beyond the demarcation point. Because the service was required to be grounded/bonded when active, those components would have to remain in place. NEC Article 820.25 also addresses this issue.

15.     I can locate a portion of the building grounding electrode system, but to make the connection between the service cable and the ground I must run the grounding conductor exposed in a finished basement. My customer tells me I cannot run the wire where it is visible, what do I do?

A)      Explain why a ground is necessary, attempt to relocate the drop so as to have a minimum of exposed wire, install the grounding conductor in wire mold, or do not install the service.

16.     What is an Intersystem Bonding Termination (IBT) and how is it applied?
A)       The NEC introduced the Intersystem Bonding Termination (IBT) and expanded and refined its concept in the 1999, 2002, 2005 and 2008 editions. The NEC made grounding to the IBT a first choice when available in Article 820.100 of       the 2008 NEC.  Newer homes should have IBT points accessible for the attachment of grounding conductors. See Article 820.100(6) B)(1)

17.     What is the preferred connection point for attaching the grounding conductor?

A)      See NEC Articles 770.100, 800.100 and 820.100 which specify that:

1.       If the building or structure served has an intersystem bonding termination (IBT), the grounding conductor shall be connected to the IBT, and
2.       If the building or structure served has no IBT, the grounding conductor shall be connected to the nearest accessible location specified in the list at Article 820.100(B) (2).

18.     Is it permissible to attach the ground conductor to metallic water pipes?

A)       Yes, Article 250.52 of the NEC requires internal metallic water piping to be part of the building electrode system. It also allows for attachment of grounding conductors to “the grounded interior metal water piping system within five feet from its point of entrance to the building.”

19.       May I attach a ground wire to the cable clamp at the load side of the electrical meter?
A)       Yes, this is covered in the NEC; Article 820.100(6)(B)(C) Electrode Connection (referenced to 250.70 Methods of Grounding and Bonding Conductor Connection to Electrodes). The grounding conductor is required to be connected to the grounding electrode by a “listed” connector or clamp. If it is not listed for the intended purpose it cannot be used.

20.     You have made reference in previous questions to use of grounding conductors of sufficient ampacity to effectively ground the service cable(s). Please give examples of appropriately sized grounding conductors.

A)        See NEC Article 820.100(A) Grounding Conductor. Copper grounding conductors are generally assumed and required by the NEC to be listed. Aluminum wire must be one AWG size larger. NEC Article 240.4(D)(3-7) and Table 310-17 provide technical specifications for wire size.
            It is important to note the following:

                    1.       The grounding conductor shall not be smaller than No.14 AWG.
                   
                    2.      The bonding conductor must be at least 6 AWG.

            Note:    NEC Table 310-17 lists current carrying capacity of single insulated copper conductors in free air for specified conductor temperature increases. A temperature rise to 60oC (140oF) is considered to be maximum in that which follows:

                              No. 14 AWG         25 Amperes
                              No. 12 AWG         30 Amperes
                              No. 10 AWG         40 Amperes
                              No.  8 AWG          60 Amperes
                              No.  6 AWG          80 Amperes

          B)     While NEC Article 820.100 (A)(2) permits the use of solid or stranded grounding conductors, field experience has shown that stranded conductors of the sizes normally used in coaxial cable grounding cannot be securely gripped by clamps commonly used for grounding. The tendency of the stranded conductor to fray or loosen in the clamp can prevent achieving and maintaining a secure mechanical and electrical connection. Therefore, the use of stranded grounding conductors sized No. 6 AWG or smaller is not recommended.

 21.     When splitting a coaxial cable to serve two, three, or four apartments in a multiple dwelling unit; must each apartment service cable be grounded individually?

A)        Splitters that are listed for the purpose would be sufficient for all cables attached to it. . You should not install ground blocks in the drops following the splitter.

 22.     Where service to a multiple dwelling unit is provided by a hardline coaxial drop feeding a building distribution amplifier where should the ground be installed?

A)        Article 820.3 (A) requires the grounding shall be as close to the building entry point as practicable. Often that is at the input of any building amplifier used. The ground will not be interrupted due to servicing of the amplifier or rearranging of splitters or taps at its output.

 23.     Are installations in mobile home and manufactured housing parks accomplished in the same way as are house drops?

 A)       The NEC addresses additional requirements for Mobile homes in section 820.106. Mobile home and manufactured housing present some unusual installation problems for coaxial cable systems.  Electrical installations in manufactured home parks and recreational vehicle (RV) parks are covered by Articles 550, 551 & 552 of the NEC. You should be aware that some older units and parks may not be wired in compliance with the most recent Code. Therefore, it is critical that caution is exercised at each step of the installation. The requirements for grounding and bonding of telecommunications and coaxial services at mobile homes are addressed in Articles 800.106 and 820.106

          Grounding. Grounding shall comply with Articles 800.106(A)(1) & (A)(2) and 820.106(A)(1) & (A)(2).

          1. Where there is no mobile home service equipment located within 9.0 m (30 ft) of the exterior wall of the unit it serves, the coaxial cable shield ground or surge arrester ground, shall be connected to a grounding conductor in accordance with Article 820.100 (B)(2)or 800.100 (B)(2).

          2. Where there is no mobile home disconnecting means grounded in accordance with Article 250.32 and located within 9.0 m (30 ft) of the exterior wall of the unit it serves, the coaxial cable shield ground, or surge arrester ground, shall be connected to a grounding conductor in accordance with Article 820.100 (B)(2) or 800.100 (B)(2).

           Bonding.  The primary protector grounding terminal, coaxial cable shield grounding terminal, surge arrester grounding terminal, or grounding electrode shall be connected to the metal frame or available grounding terminal of the mobile home with a copper grounding conductor not smaller than 12 AWG under any of the following conditions:

          1. Where there is no mobile home service equipment or disconnecting means as in Article 800.106(A) or 820.106 (A)

          2. Where the mobile home is supplied by a cord and plug connections to grounding electrodes shall comply with Article250.70.

 24.     All preceding questions have dealt with aerial installation of coaxial cable. Are there specific additional requirements for residential underground coaxial cable installation?

 A)       Yes, along with the grounding requirements of the NEC, Part 3 of the NESC has additional Safety Rules for Underground Lines.

          a.           Underground service where the CATV cable is installed in metallic conduit in contact with the earth for ten or more feet may use the conduit as a grounding electrode; however, the metallic cable sheath must be bonded to the conduit and to the customer's electrical service grounding system.

          b.           Underground service where the CATV cable is of the direct burial type or where the conduit used is non-metallic, the CATV cable must be grounded at the nearest point to building entry.

          c.           Where trunk and/or feeder cables are installed to joint trenches, i.e., telephone and power, CATV cable must be bonded to power grounds where power grounds exist and each power supply location. The installation must comply with applicable NEC Code provisions.

          d.          Where trunk and/or feeder cables are buried separate from utilities, the system must be grounded utilizing No. 6 AWG copper grounding conductors and eight feet by 5/8 inch grounding electrodes spaced not more than 1/4 mile apart and at every power supply location.

          e.           Where trunk and/or feeder cables are buried in areas defined as agricultural areas, Department of Agriculture specifications apply. A permit is required. Minimum burial depth of cable is 40 inches. The cable must be grounded as above.

          f.            The NESC defines CATV cables as "communications lines". As such, these cables should be buried at the depths indicated by Section 353D (normally 24 inches). However, under some circumstances a lesser depth maybe appropriate. Some local governments (such as New York City) require the installation of protective metal plates above the cables. It is your responsibility to check local regulations before proceeding.

 25.     My company serves an area where there are many shore-side facilities such as private docks and marinas where people want telecommunications service afloat. Is there an NEC requirement for installations such as these?

 A)       Yes, Article 555 of the NEC covers electrical installations in Marinas and boat yards. Important points to consider in providing telecommunications service to a boat or to a dock-side office, etc. are as follows:

          a.           Grounding of a service cable must not rely on connection to metal raceway, conduit or boxes.  Grounding may be accomplished only by connection to the grounding terminal in the dock-side electrical service equipment enclosure. Note: Telecommunications personnel should not make this connection. It should be addressed by a licensed electrician.

          b.          Where telecommunications service is supplied to a boat or other floating unit, care must be taken to maintain safe clearances under conditions of changing water levels.

          c.           Care must be taken in installation of telecommunications cables to avoid contact with masts, booms, cranes, etc.

          d.           Grounding continuity between a floating unit and an earth ground on shore must be maintained.

 26.       My company serves an area where many large apartment buildings are served by hardline coaxial feeder cables used as drop cable. Are there devices other than pipe straps or conduit clamps suitable for grounding these drops?

A)        Yes, many manufacturers have developed listed devices that are useful in this application. Consult your equipment supplier.

27.      Customers and contractors remove my grounding conductors as work is being done on siding, etc. How may I prevent that?

A)        You probably can not.  However, after installing a ground you should tag it with a conspicuously colored plastic tag with a short "Caution-Do Not Remove" message and your service department telephone number. This should help to reduce the problem.

28.       You recommend that installed grounds be periodically checked. This takes more time on service calls. Why do you recommend this practice?

A)        Many ground connections become loose after a time. This allows corrosion to form under the connection increasing electrical resistance and reducing grounding effectiveness. Measurements of sheath current often indicate no current until the ground connection is cleaned and tightened. Office of Telecommunications inspectors make resistance measurements of grounding connections and from time-to-time report on these measurements. Measurements made before and after tightening screws and clamps and removing corrosion show significant improvements in grounding effectiveness. Therefore, we continue to recommend that telecommunications technical personnel (after the initial installation) routinely inspect the grounding system at subscribers' homes; removing corrosion and tightening fittings,clamps, and screws to restore the best possible electrical path between the drop cable and the grounding electrode.


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