250.94 Bonding for Communication Systems.
Code Change Summary: Another bonding method was added for intersystem bonding terminations (IBT). As well, a new exception allows the IBT to be omitted where communications systems are not likely to be used.
The rules in 250.94 are all about proper termination of communications system bonding terminals. If done correctly, properly terminating the bonding terminals in a communications system results in preventing a situation where a difference in voltage potential exists between the premises electrical system and the communications system.
In the 2014 NEC®, the only bonding method permitted is an intersystem bonding terminal (IBT). The IBT is only for bonding communications systems and cannot be used for bonding anything else other than communications systems. The IBT is still permitted in the 2017 NEC®.
The IBT is required to be installed external to the service equipment, or for buildings supplied by other than a service, adjacent to the disconnecting means for the building or structure. Having the IBT external to the service or disconnect ensures that those installing communications systems can access the terminal without the need to open an electrical panel that may not be covered within the scope of their license.
In the 2017 NEC®, an additional bonding method is recognized by new text in 250.94(B). The new text allows connections to an aluminum or copper busbar not less than 1/4 in. thick × 2 in. wide and of sufficient length to accommodate at least three terminations for communication systems in addition to other connections. This is already commonly used in multi-occupancy commercial buildings for grounding electrode conductors in accordance with 250.64(D) & (F).
Using the new method would permit communications system bonding conductors as well as other bonding conductors to land on this common busbar. This may provide relief for those installing new gas piping, vacuum or compressed air lines that require bonding. Often a new gas water heater or other appliance is installed on an existing building and proper gas pipe bonding is never done since the scope of the license for the gas piping installer may not allow opening the electric panel to make grounding or bonding terminations.
Below is a preview of Article 250. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC® edition of NFPA 70.
2014 Code Language:
250.94 Bonding for Other Systems. An intersystem bonding termination for connecting intersystem bonding 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: (See NEC® text for six bonding requirements)
2017 Code Language:
250.94 Bonding for Communication Systems. Communications system bonding terminations shall be connected in accordance with (A) or (B).
(A) The Intersystem Bonding Termination Device. An intersystem bonding termination (IBT) for connecting intersystem bonding conductors 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. If an IBT is used, it shall comply with the following:
See NEC® text for six bonding requirements mentioned in 250.94(A). (These did not change but they only apply to the intersystem bonding terminal, NOT the “other means” which is new in 250.94(B))
N (B) Other Means. Connections to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1/4 in. thick × 2 in. wide) and of sufficient length to accommodate at least three terminations for communication systems in addition to other connections. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector. If aluminum busbars are used, the installation shall also comply with 250.64(A).
Exception to (A) and (B): Means for connecting intersystem bonding conductors are not required where communications systems are not likely to be used.
Informational Note: The use of an IBT can reduce electrical noise on communication systems.