Why 6-position plugs in 8-pin jacks cause 4-aspirin headaches

July 1, 2003
Are you seeing damage to 8-pin modular jacks caused by the insertion of 6-position plugs? Universities see this problem every semester.

Are you seeing damage to 8-pin modular jacks caused by the insertion of 6-position plugs? Universities see this problem every semester. Student moves into dorm room, unpacks and plugs in telephone, then sets up and plugs in computer. But the phone is dead and there is no data connection. Oops! Switch the plugs to the proper jacks, and voila!—the phone now works but still not the data connection. Why? Most likely, the shoulders on the 6-position plug, on the end of the silver-satin line cord, flattened pins 1 and 8 inside the data jack. And since almost all data in dorms is Ethernet—and Ethernet uses pins 1, 2, 3, and 6—the bent pin 1 in the data jack is the problem.

If you also have to change a lot of damaged 8-position modular jacks, TIA TR42 wants to know. Send your comments to the Chair of the TIA Technical Committee TR42, Bob Jensen at [email protected] before August 1. Samples of failed jacks should be sent to Bob Jensen at Fluke Networks, Houston Building, 9015 Mountain Ridge Road, Suite 230, Austin, TX 78759.

While manufacturers will not be happy at the prospect of retooling their production lines to produce slightly different 6-position plugs, TR41.9 Technical Regulatory Considerations has agreed to address this issue by tightening the requirements on the 6-position plugs, if they decide that the problem is "significant."

TR41.9 is responsible for maintaining the TIA 968-A, Telephone Terminal Equipment, Technical Requirements for Connection of Terminal Equipment to the Telephone Network—formerly known as FCC Part 68—which specifies technical criteria for terminal equipment for direct connection to the public switched telephone network.

But the plug may not be the only culprit here. TIA/EIA-568B.2 Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components, Section 5.3.5 Reliability states, "To assure reliable operation over the usable life of the cabling system, the connecting hardware used to terminate to 100-ohm balanced twisted-pair cabling shall meet the requirements of Annex A."

Annex A, Reliability Testing of Connecting Hardware for 100-ohm Balanced Twisted-Pair Cabling, states, "For connecting hardware with 8-position modular connectors, the modular connection shall comply with the Level A reliability requirements of IEC 60603-7." The IEC 60603-7 8-position modular jack, recognized as the generic connector interface for all applications using balanced twisted-pair cabling, is required to endure 750 insertion and withdrawal cycles without failure.

The problem: 750 insertion and withdrawal cycles with what? 8-position plugs, 6-position plugs, or some combination of each? There are no provisions for testing with 6-position plugs.

The ability for the jack pins to recover from the plug insertion depends on the material that the pins are made from and the amount of pin-flex the jack design accommodates. Translation—not all jacks will experience damage.

As designers, specifiers, installers, and end users, we have control of the quality of the jacks installed as part of our cabling systems. But the plugs on the equipment cords packaged with everything from telephones to fax machines are controlled by the manufacturers of those products.

This problem has prompted many connecting-hardware manufacturers to change their jack designs. Ask the manufacturer if their 8-position modular connector contacts are configured to survive insertion of a compatible 6-position plug.

TE update

So, where do we stand on the characterization of TIA's latest new space?

We know the function of the telecommunications enclosure (TE)—to serve as a common access point for backbone and building pathways and be able to contain telecommunications equipment, cable terminations, and associated cross-connect cabling.

We know where to locate the TE—permanently secured to the building structure, as close as practicable to the center of the area served.

We know the accessibility and access-control requirements for the TE—easy for authorized access but controlled against unauthorized access. I read this as, "not behind a row of filing cabinets, and with a lock on a suitably sized door."

We know that the TE must not damage cables—we are to use grommets, bushings, and suitable cable-management hardware to protect against sheath abrasion and conductor deformation.

We know the size of the floor area a TE can serve—not more than 3,600 square feet.

We know the size of the TE—large enough to satisfy immediate and future cabling and equipment space needs while being mindful not to exceed cable bend radii.

We know that metallic parts of the TE must be bonded to ground.

We know to install TEs under good lighting and away from drippy (or potentially drippy) sprinkler heads.

Here are some outstanding TE questions and my "best guess" answers:

Q: How many 20-A, 120-V, non-switched, AC duplex electrical outlet receptacles are required to be installed at the TE? One for equipment and one for convenience?

A: One for equipment. Convenience outlets are required in a TR for ... well ... convenience. If a TE is used in a work-area cluster, then there will already be convenience outlets available.

Q: Are the electrical outlet receptacles required to be inside the TE or just nearby?

A: Sorry, no insight here. This one could go either way.

Q: Will the temperature and humidity requirements for equipment rooms (continuous operating temperature ranges of 64º F to 75º F with 30% to 55% relative humidity) be extended to the TE?

A: No, definitely not. Ironically, there are no temperature and humidity requirements for telecommunications rooms in the current TIA-569B draft, and the equipment required to regulate such an operation environment costs around $15,000—which is one of the reasons why you have not seen these same requirements for TRs.

Q: Can TR42.1 stall the publication of TIA-569B until they complete their Addendum 5 to TIA-568B.1, tentatively titled Implementation of Telecommunications Enclosures? The early draft appears to simply add the phrase "and telecommunications enclosure" to each appearance of the phrase "telecommunications room" for all of TIA-568B.1

A: No. For a few months at least, there will be a new space described in TIA-569B with no guidance available in TIA-568B.1 on how it should be properly used in a commercial building cabling system. Until then, remember to use responsibly.

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Donna Ballast is BICSI's standards representative, and a BICSI registered communications distribution designer (RCDD). Send your questions to Donna via e-mail: [email protected]

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