September, 2010
Inspection News and Views from the American Society of Home Inspectors

NEC 250.94 – Bonding for Other Systems


Bonding for Other Systems, as covered in Section 250.94 of the National Electrical Code, is a mandatory requirement that demands serious attention by electricians, electrical contractors, electrical inspectors and others associated with the design and construction of buildings and structures. It is also an important issue for those companies and individuals involved with the delivery of communications and entertainment services to their customer's facilities. And, it should not escape the attention of home inspection professionals. Compliance with this Code rule is an essential and necessary part of any electrical installation and is applicable to ALL types of buildings and structures. This article addresses 250.94 as it applies to one- and two-family dwellings, although most of the information provided can be applied to all types of buildings and structures.

The term 'bonding' is used throughout this article as that is the operative term in 250.94. It is recognized by the author that grounding is also accomplished as a direct result of meeting this requirement.

Why bond other systems?

First and foremost, bonding for other systems is an electrical safety concern. After all, that's what the National Electrical Code is all about. The 2008 NEC Handbook tells us that separate systems must be bonded together to reduce the voltages that can occur between them due to lightning or accidental contact with power lines. Lack of proper bonding can result in a severe shock and fire hazard. These voltages, where proper bonding is not in place, are brief events that can easily reach thousands of volts—even tens of thousands of volts in some cases.

In addition to the safety concerns, the increased use of electronic equipment in residential dwellings, some of it quite sensitive, has made proper bonding and grounding of all systems that much more important. Improper and inadequate bonding and grounding have a direct and negative impact, not only on safety, but also on the reliability and performance of equipment and systems.

Section 250.94 addresses the intersystem bonding required at the service entrance of a building or structure. The Code requires primary protectors and/or ground blocks at the point of entrance to a structure where cables containing metallic conductors are used to bring communication, entertainment and similar services into the structure from the outside. These protection devices are then required to be bonded to the power (electrical) bonding and grounding system. This requirement certainly includes telephone companies, cable television companies and companies delivering services that require externally mounted antennas.

The Code points out that telephone services, cable television services and antenna-based services are typical of those other systems that must be bonded together, and does not limit the definition of other systems to just those services. The rule applies by reference or inference to other systems such as those employed for security, fire, irrigation, lightning protection, etc.

The interior bonding and grounding requirements for communications and other sensitive electronic equipment installed within buildings and structures are addressed elsewhere in the Code and in other standards.

Enter the intersystem bonding termination

Section 250.94 has been substantially revised in the 2008 Code, thereby affecting all new installations and existing installations where alterations are made. As part of this revision, the Code has identified a new device called the Intersystem Bonding Termination or IBT. The 2008 NEC defines the IBT as "a device that provides a means for connecting communications system(s), grounding conductor(s) and bonding conductor(s) at the service equipment or at the disconnecting means for buildings or structures supplied by a feeder or branch circuit."

Photo: IBT Device. Photo courtesy of Arlington Industries.

The photograph above is an example of an IBT device that is attached to the electrical system's grounding electrode conductor (the large, bare conductor on the right). Insulated conductors from three 'other systems' are connected to this termination device. There is a cover for this device that is not shown here.

The IBT provides a single, easily identifiable, physical termination device to which bonding (grounding) conductors of all other systems are to be connected. No struggle to locate an acceptable bonding location. No need for additional listed hardware to facilitate the connection. The installer simply connects the protection device's bonding (grounding) conductor to the IBT terminal and … DONE!

The IBT will, over time, reduce significantly the number of hardware application and connection point violations committed by installers of other systems. It will also bring some order to the grounding and bond process as all providers are now required to bond to the same bonding point, at least on new structures.

The requirements of Section 250.94 are not complicated and are outlined here.

From the 2008 Code (NFPA 70), Article 250, Part V. Bonding, 250.94 Bonding for Other Systems.

The Code first states the mandatory requirement for an intersystem bonding termination: that it must be external to enclosures (other than its own optional enclosure or cover); and acceptable mounting locations.

An intersystem bonding termination [IBT] for connecting intersystem bonding and grounding conductors required for other systems shall be provided
  • external to enclosures

    The IBT cannot be installed inside of an electrical enclosure, especially one that would be off-limits to technology workers. It can be located within its own nonmetallic enclosure or have a nonmetallic cover.
  • at the service equipment

    The IBT is to be located as close to the service equipment (electrical service entrance point) as practicable, and preferably on the outside of one- and two-family dwellings. It is almost always located inside of most other types of buildings and structures.
  • or metering equipment enclosure [the underlined portion will be included in the 2011 Code]

    The metering equipment enclosure has been an acceptable bonding location for a long time. This additional language will clarify that acceptability.
  • and at the disconnecting means for any additional buildings or structures.

    An IBT is also required at any additional building or buildings on the premises that are served by feeders or branch circuits (typically served from a primary or principal building or structure), and should be located as close as practicable to the disconnecting means of those additional buildings or structures.
Next, the Code addresses IBT accessibility, capacity, and the concern for avoiding physical interference with access to electrical enclosures.

The intersystem bonding termination shall …
  • be accessible for connection and inspection

    The IBT cannot be hidden or located in a place that is not readily accessible to installers and inspectors … Readily accessible means capable of being reached quickly for operation or inspections without requiring one to climb over or remove obstacles or resort to ladders and so forth.
  • have the capacity for connection of not less than three intersystem bonding conductors.

    The IBT is typically a bonding bar having a minimum of three connection points for communication system bonding and grounding conductors. It will also have a connection point to accommodate a 6-AWG or 4-AWG bonding/grounding conductor that bonds it to the electrical system ground.
  • not interfere with opening a service or metering equipment enclosure.

    A common violation is found where a connection device used to facilitate communication system bonding is improperly attached to a metering equipment enclosure and interferes with removal of the enclosure cover.
And finally, the Code specifies acceptable methods for establishing the intersystem bonding termination.
The intersystem bonding termination shall be one of the following:
  1. A set of terminals securely mounted and electrically connected to the meter enclosure or service equipment enclosure. The terminals shall be listed as grounding and bonding equipment [the underlined portions will be included in the 2011 Code].

  2. A bonding bar near the service equipment enclosure, meter enclosure or raceway for service conductors. The bonding bar shall be connected with a minimum 6-AWG copper conductor to an equipment grounding conductor(s) in the service equipment enclosure, meter enclosure or exposed nonflexible metallic raceway.

  3. A bonding bar near the grounding electrode conductor. The bonding bar shall be connected to the grounding electrode conductor with a minimum 6-AWG copper conductor.

The language from the previous edition of the Code is now the exception in the 2008 Code and still applies for identification purposes where installations were made prior to implementation of the 2008 Code. The exception is not included here because any new installation, and any alteration or repair of an existing installation, is required to comply with the current (2008) Code. While this new requirement does not apply to existing installations that remain unaltered, most structures, dwellings in particular, can be upgraded to comply with the current rule without great difficulty or expense. In many cases, such an upgrade is likely to result in improved bonding, thereby enhancing safety and improving the protection, reliability and performance of other systems.


Illustration: Code-permitted ground points for the IBT device.


Finally, the installers of other systems will have a designated location and device to which they are to connect their bonding (grounding) conductors. It is going to take some time, but as the IBT becomes more commonplace, it should dramatically reduce the number of bonding and grounding violations associated with installations of other systems.

Intersystem Bonding Termination devices are available from a number of sources to facilitate compliance with Section 250.94. Manufacturers include Arlington Industries, Burndy, Electric Motion Company, Erico, Greaves, Harger, Ilsco, Thomas and Betts, and others. Most electrical distributors stock one or more of these products.

The author suggests that a best-practice IBT deployment would include an interior IBT device at the service equipment location — typically the main electrical panel — and an exterior IBT device at the service entrance location. Such a plan will accommodate almost every possible grounding and bonding scenario for one- and two-family residential dwellings. The Code requires only one such device, preferably mounted on the exterior in the case of residential structures.

The following reminder is offered to those installing or inspecting the intersystem bonding termination. Where a bonding conductor is part of the IBT installation, it should be kept as short and as straight as possible. This is essential to proper performance of any bonding and grounding system. The NEC Section tells us that they should not be any longer than necessary to complete the connection, and that unnecessary bends and loops are to be avoided.

The Minnesota Department of Labor & Industry, Construction Codes and Licensing Division sent an e-mail message to all Minnesota electrical inspectors back in November of 2006. It stated, in part, "Please be certain that an accessible means for connecting intersystem bonding is provided at the service equipment for communication systems, radio and television equipment, CATV, and rod- and dish-type antenna systems. Refer to the requirements and fine print notes at Code 250.94 … ". The requirements in 250.94 have been altered since this message was sent, but the imperative has not changed.

A two-page, condensed version of this article is available as a PDF and can be found on the author's website at The author encourages copying and distribution of that document to all interested parties, particularly electricians and electrical contractors.

A note to home inspection professionals: Part of what makes a dwelling a safe environment is properly bonded and grounded telephone, cable TV and antenna-based services. It is disturbing how often this is not the case for one or more of the communication and entertainment services delivered to the typical dwelling. The author plans to address this topic in a future article.

A Little History

The author does not know (as of this writing) just when the 'bonding for other systems' rule first appeared in the Code. The requirement for protectors on outside communication and signaling circuits, and the bonding of those protectors to the electrical system, dates back to the original National Electrical Code, first published in 1897. The rule has been in the Code for a number of years. It moved around some, being located in Section 250-71(b) of the 1993 Code and in Section 250-92(b) of the 1999 Code before finding what appears to be its dedicated and permanent home in Section 250.94. It remained relatively unchanged during that period of time, with minor additions as various new technologies made their appearance.

The Code has, for some time, required that a facility must have at least one of the following means to provide for bonding of other systems:

  1. A non-flexible metal raceway, or

  2.  An accessible grounding conductor, or

  3. An "other means" [such as a properly bonded and grounded 6-AWG pigtail per 250.94, FPN No. 1]
Electrical-Pre2008NEC.jpgThe bonding (grounding) conductors for other systems can then be connected to one of these points using listed devices or fittings (hardware) that are identified for the specific purpose.
Until a few decades ago virtually every residential dwelling had a metal service entrance raceway and an accessible grounding electrode conductor. The intent of bonding for other systems was accommodated as part of the basic electrical installation without giving it a thought, even before the Code addressed it in a specific fashion. In any case, bonding for other systems has been largely ignored by electrical installers and electrical inspectors, particularly where residential construction is involved. And …communication and entertainment service providers bonded their protection devices to the most convenient bonding point they could find. In too many cases, these bonding connections are violations of the Code.


Change is Inevitable

There have been many changes in the electrical industry in recent years that now mandate more careful attention to this rule by all concerned. These changes have affected all types of buildings and structures, and certainly residential dwellings.

1. The replacement of the non-flexible metal raceway with PVC raceway as the service entrance raceway of choice.
This obviously involved savings in material and labor, and was a more suitable choice as newer electrical services are much more likely to be located underground.

2. The disappearance of the accessible grounding electrode conductor on newer homes. There are a number of reasons for this occurrence as electrical services and grounding requirements have evolved, not the least of which is the advent of the mandatory use of the concrete-encased electrode (rebar in the footing).

The accessible grounding electrode conductor may have well have been the most popular, and most utilized, bonding point by telephone companies for many decades.

3. The metering enclosure is located at the utility transformer near the property line rather than on or at the dwelling. This is an increasingly common occurrence in rural areas.

Metal meter enclosures often have been the one available, accessible and Code-permissible bonding point on many newer dwellings. Bonding to a meter enclosure probably comes in second to the accessible grounding electrode conductor as a communication system bonding point.

The 2008 NEC Handbook points out that with the increased use of plastic water pipe, the increasing tendency for service equipment (often flush-mounted) to be installed in finished areas, where the grounding electrode conductor is often concealed, and the increase of plastic service-entrance conduit, communications and entertainment service installers no longer have access to an acceptable bonding point for connecting bonding jumpers of grounding conductors.

The lack of a suitable bonding point on many newer structures (dwellings in particular), and no doubt the lack of proper training and supervision by some entertainment and communication service providers, has resulted in large numbers of communication system bonding violations. The Minnesota Department of Labor and Industry, Construction Codes and Licensing Division, has more than amply documented these violations. The New York State Department of Public Service has also documented large numbers of such violations.