Bonding conduit sleeves

This article discusses where and how the NEC requires bonding and grounding for conduit sleeves.

03/16/2010


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Read the first article in a series from Tim Kuhlman, "Unlocking the code" , about how to decipher the National Electrical Code for easier application on design and construction projects.


Routing communications and data cabling exposed is an acceptable practice under the National Electric Code ( NEC ), providing the proper cabling type has been selected for the defined space. When exposed cabling transitions through a wall, floor or wall cap, conduit sleeves or conduit stubs are installed to provide protection to the cabling. When a conduit sleeve or stub is installed, does it have to be bonded to the building grounding system?

For exposed routed cabling, the nearest grounding conductor could be a few inches away or several feet away depending on the installation (see Figure 1). The sleeve may be a couple of hundred feet from the nearest telecommunications grounding bar or electrical room grounding bar.

 

Key issues

 

Grounding and bonding are two separate functions even though it is common to see the terms used interchangeably. In our example using conduit sleeves, to bond the sleeve would mean to provide electrical continuity from the sleeve to another conductor such as a cable tray, conduit, or enclosure. If the cable tray, conduit, or enclosure were connected (bonded) to the ground system, then the sleeve would be grounded by the bonding. Bonding ensures that the conductive surfaces are at the same voltage potential. Grounding the conductive surfaces places the voltage potential of the surfaces at the same value as the ground reference where the NEC defines the ground as earth.

 

The installation requirements for a telecommunications grounding system are covered in standard Telecommunications Industry Assn. (TIA) J-STD-607-A . This standard is not specifically referenced in the NEC. However, standards ANSI/NECA/BICSI/568-2006 and ANSI/TIA/EIA 568-B are referenced and both of these standards refer to the TIA J-STD-607-A (formerly EIA/TIA-607) for a telecommunications ground system. Following the 607 standard, cable trays and conduits used for distributing telecommunications cabling are bonded to a telecommunication bonding bar in the telecommunications room. The telecommunications bonding bar is bonded to the electrical system building ground. The installation requirements of the 607 standard do not change the NEC requirements or exclusions for bonding conduit sleeves and stubs.

 

Conduit is a raceway, and for the installation requirements in Chapter 3 for raceways to apply to telecommunication cabling, conduit must be specifically referenced in Articles 725 , 770 , or 800 . For Articles 770 and 800, the link back to the raceway articles in Chapter 3 is straightforward. In paragraphs 770.110 and 800.110, the code allows the cabling to be installed in raceway types permitted by Chapter 3 and installed in accordance with it. This is a broad reference to Chapter 3, allowing multiple paragraphs that address raceways to be applied. The link from 725 back to Chapter 3 for the load side of a Class 2 power supplied circuit (Ethernet) and raceways is not as straightforward.

 

Article 725 does not have a similar paragraph stating for raceways that refer to Chapter 3, although raceways are mentioned throughout the article. Article 725.154 addresses the different applications for Class 2 cables where Chapter 3 is referenced as a whole in paragraph 725.154 (B)(2) for the description of risers. It is again stated in 725.154 (E)(2) for “other wiring within buildings in raceways or other wiring.” Other paragraphs that are related to the issue of conduit sleeves and stubs can be found in paragraph 725.24, which refers to 300.4(D) for “Cables and Raceways Parallel to Framing Members.”

 

Chapter 2 is not limited in its scope in Article 725 as Chapter 3 is. Therefore, all the provisions of Chapter 2 apply. Article 770 has limiting language for Chapter 2 in paragraph 770.3. In Article 770, a section of Chapter 2 would have to be referenced in 770 for it to apply. Chapter 8, Article 800, is a standalone chapter and therefore needs a reference back to any of the NEC chapters, including Chapter 2, for Chapter 2 to apply. However, since 770 and 800 have referenced Chapter 3 as a whole for the application of raceway, then it is assumed that any of the provisions in Chapter 2 that relate to the installation of raceways apply.

 

cse1003_fbonding_fig1.gif

Figure 1: A conduit sleeve is in close proximity to a grounded cable tray. Source for all: Tim Kuhlman

 

 

Deciphering the code

 

When conduit sleeves or stubs are installed, the use of electrical metallic tubing (EMT) is a common choice. Thicker wall conduit types can be used, but the thinner EMT is allowed by the code, is easy to work with, and provides the necessary protection to the cabling. Figure 3 is a representation of cables parallel to framing members as described in paragraph 300.4(D). For the telecommunications cabling, the conduit stub extends to just beyond the top of the wall cap.

 

The conduit stub as shown in Figure 3 is not a requirement of the code. A steel plate could be used to protect the cable or the cable could be installed 1e wall cap to protect the cable.

 

Figures 1, 2, and 4 show three scenarios where conduit sleeves are used to extend through a wall and floor to provide cable protection. In Figure 1, there is a transition from cable tray to conduit sleeves and back to tray on the other side of the wall. In this example the sleeve is in close proximity to the cable tray. In Figure 2, there is a significant distance from the cable tray to the conduit sleeves. Figure 4 shows the sleeves penetrating a floor. For each of these scenarios, assuming the wall and floor are not fire-rated assemblies, the conduit sleeve and cable tray can be considered a non-current-carrying conductor. The question remains, “What are the bonding requirements for these scenarios?”

 

 

 

cse1003_fbonding_fig2.gif

Figure 2: This figure shows the conduit sleeve not near a grounded surface.

For the scenarios using cable tray, it will be assumed the cable tray is grounded per the requirements of 392.7 and can perform as a grounding conductor outlined in the provision of 392(B). The general performance requirements for grounding and bonding are addressed in article 250.4. Paragraphs 250.4(A)(2) and 250.4(A)(3) state “non-current-carrying conductive materials enclosing electrical conductors . . . shall be connected to earth (ground) and shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.” Under Chapter 2 Part V Bonding, paragraph 250.96 (A), the bonding requirements for electrical continuity are repeated.

 

Paragraph 300.10 addresses the electrical continuity of metal raceways and enclosures. The paragraph requires metal raceways and other metal enclosures to be “metallically joined together into a continuous electrical conductor . . . so as to provide effective continuity.”

In line with the previous paragraphs, it would appear the sleeves would have to be bonded. The key to not having to bond these is stated in Paragraph 300.10 Exception 1: “short sections of raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be electrically continuous.” This exception in the code appeared in the 1999 issue of the NEC.

 

Paragraph 392.6 [Cable Tray] Installation allows for the cable tray system to be mechanically discontinuous, but electrical continuity must be maintained. Figure 1 shows the cable tray system being interrupted by the wall. A bonding wire can be routed through the sleeves to provide electrical continuity between the trays' sections or the bonding wire can be connected to the metallic EMT and included as part of the tray system. For the scenario shown in Figure 1, it would be prudent to bond the conduit sleeves.

 

cse1003_fbonding_fig3.gif

Figure 3: This figure shows a conduit stub or sleeve in wall.

 

 

In Figure 2, the argument can be made that the cable tray system is not extended to the conduit sleeves. The cable is routed exposed. Neither sleeves nor the J-hooks supports require bonding to the system ground.

 

Paragraph 250.4(A)(4) states that “normally non-current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.” The conduit sleeves and the support wire can be considered non-current-carrying conductors. However, as Figure 2 illustrates, the sleeves and J-hooks are unlikely to become energized, negating the requirements for these to be bonded together or to the tray system. Figure 4 does not show another raceway or cable tray in the proximity of the sleeves. Per paragraph 300.10 Exception 1, these sleeves would not require bonding.

 

Items to note

 

Often, the wall or floor that requires a sleeve to protect exposed cables is also a fire-rated assembly requiring fire stopping. In such cases, the question is whether the fire stopping sleeve or assembly is required to be bonded and grounded. There are two issues to consider. First, does the sleeve meet any of the requirements already discussed for conduit sleeves as isolated sections of conductive material providing protection or part of a bonded system such as the cable tray? The second issue is unique to the fire stopping assembly. Unless it is an engineered solution, the fire stopping assembly is a UL-classified product.

 

A bonding conductor and fastener cannot be arbitrarily connected to a fire stopping assembly without the assembly or the manufacturer of the assembly already have taken into account a method for bonding. If the assembly needs to be bonded, a product should be selected that already has a bonding provision noted by the manufacturer. The bonding and grounding of a fire-stopping assembly cannot interfere with the design function of the assembly.

 

 

 

cse1003_fbonding_fig4.gif

Figure 4: This figure shows conduit sleeves through a floor not near a grounded surface.

Additionally, sleeves are also used to penetrate walls where there is anticipated movement in the structure from one side of the wall to the other. This could be the case where there is a structural isolation break in a building or when two separate buildings share a common wall. Just as the exposed cabling needs to be designed with cable slack for building movement, this also applies to the bonding conductors passing through or attached to the sleeves.

 

A sleeve may be used to transition through a wall or floor where there may be conditioned space on one side of the sleeve and an unconditioned space on the other side. Per article 300.7(A), the sleeve must be sealed and filled with an approved material to prevent warm, moist air from condensing on the cold surface.

Conclusion

As shown in Figure 3, the requirement to install a conduit stub for telecommunication cabling may be a requirement by a local authority having jurisdiction or building specification by the system owner. The same requirement may exist for the sleeves shown in Figures 2 and 4. The NEC does not require these sleeves to be bonded and grounded. Because this exception appeared in only the three latest revisions of the code, legacy owner specifications and code officials may still require the sleeves to be bonded. In an application as shown in Figure 3, where the sleeve is part of a bonded system, bonding of the sleeve is required. If the sleeve in Figure 3 is not part of the bonded system, but is in close proximity of bonded and grounded surfaces, it would be prudent to bond the sleeves.


Click here for the first article in this series from Tim Kuhlman about how to decipher the National Electrical Code for easier application on design and construction projects.


Table 1: Reference table

 

Article 725 Class 2

Article 800 Communications (telephone)

Article 770 Fiber optic cable

725.3: Compliance with other articles and sections 725.154: Applications of Class 2 cables 725.154 (E) (2): In raceway or in accordance with other wiring methods in Chapter 3 Chapter 2 not limitedEntire section applies

90.3: Compliance with other articles and sections for Chapter 8 800.110: Raceways for Communication Wires and Cables. Chapter 3 applies for permitted raceways and their installation Article 250 applies for the grounding and bonding or raceways with all of Chapter 3 being included for raceways

770.3: Compliance with other Articles and Sections 770.110 Raceways for Communication Wires and Cables Chapter 3 applies for permitted raceways and their installation Article 250 applies for the grounding and bonding or raceways with all of Chapter 3 being included for raceways

300.10: Electrical continuity of metals raceways Exception 1: Short sections of sleeves

300.10: Electrical continuity of metals raceways Exception 1: Short sections of sleeves

300.10: Electrical continuity of metals raceways Exception 1: Short sections of sleeves

250.4: General Requirements of Grounding and Bonding

250.4: General Requirements of Grounding and Bonding

250.4: General Requirements of Grounding and Bonding

250.96: Bonding of other enclosures

250.96: Bonding of other enclosures

250.96: Bonding of other enclosures

392.6: Cable Tray Installation

392 not referenced in 800 but listed in table 392.2(A)

392 not referenced in 800 but listed in table 392.2(A)

392.6: Cable Tray Grounding

392 not referenced Bonding required by J-STD-607

392 not referenced. Bonding required by J-STD-607

 




 

 

Author Information

Kuhlman has 20 years of experience in the design and construction of telecommunications infrastructure. He is a member of Consulting-Specifying Engineer's Editorial Advisory Board.

 

 

 

 

Conditions

 

 

• A short section of conduit or raceway

 

 

 

• The conduit sleeve is used to provide protection to exposed routed cables

 

 

 

• The sleeve or stub is routed horizontal through a wall, vertical in a wall, or vertical through a floor.

 

 

 

• DEFINITIONS:

 

 

 

Bonded: “Connected to establish electrical continuity and conductivity”—NEC 2008 Article 100 Definitions

 

 

 

• Grounding: “Connected to ground or to a conductive body that extends the grounding connection”—NEC 2008 Article 100 Definitions

 

 

 

• Conduit stub: Not defined by the NEC. Common definition: a short section of conduit; similar to a conduit sleeve but may be unconnected to another conduit, box, or fitting at one end

 

 

 

• Conduit sleeve: Not directly defined by the NEC. Implied definition: a fitting providing protection to wiring and cable. Can be metallic or nonmetallic. A protective sleeve is typically not connected to another piece of conduit, box, or fitting at either end.

 

 

 

 

 

NEC root articles

 

 

• Data Cabling: UTP Category 5e, 6, 6a common for Ethernet LANs: Article 725 for Class 2 & 3 circuits

 

 

 

• Communications Cabling: UTP Category 5e, 6, 6a common for telephone circuits: Article 800

 

 

 

• Fiber Optic Cabling: Article 770

 

 

 

• Key NEC Article: 300.10 Exception 1: “Short sections of raceways used to provide support for protection of cable assemblies from physical damage shall not be required to be electrically continuous.”

 

 

 

• TIA J STD-607-A: Commercial Building Grounding (Earthing) and Bonding Requirements for Telecommunications.

 

 



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