Lesson Six, Iowa State Telecom installation correspondence course: cable termination practices are vital for transfer of information.
Insulation Displacement Connection (IDC) termination is the recommended method of copper termination recognized by ANSI/TIA/EIA-568-A for UTP cable terminations. Commonly called punch-down connections, these connections require the use of a small punch-down tool to properly secure the cable to terminal block.
Punch-down connections remove or displace the conductor's insulation as it is seated in the connector. During termination, you press the cable between two edges of a metal clip, which displaces the insulation and exposes the copper conductor. This ensures a solid connection between the copper conductor and terminating clip. Screw-type terminal faceplates commonly used in voice applications are not recommended by ANSI/TIA/EIA-568-A for UTP terminations.
A crimp-style connector for copper and coaxial cable is dependent upon the shape and diameter of the cable. The cable may be round or flat. You must ensure you've selected the proper crimp connector for your specific cable.
The following types of cable are currently recognized by the ANSI/TIA/EIA-568-A standard for use in premises cabling:
- 100 ohm unshielded twisted-pair copper cable (UTP)
- 100 ohm screened twisted-pair copper cable (ScTP)
- 150 ohm shielded twisted-pair copper cable (STP-A)
- Optical fiber cable
PRETERMINATION FUNCTIONS Proper preparation for cable termination not only improves the quality of the job but also decreases the amount of time required for termination. Here's how it works. First, organize the cable by destination. Place the cable to be terminated in close proximity to the point of termination, and properly identify it to make sure it's terminated in the correct position.
Forming and dressing the cable involves properly aligning and positioning the cables in a neat and orderly manner for termination. You must also take into account the length of cable needed to reach the termination. In determining this length, you should leave enough slack in case you need to reterminate for any reason. Cable connection is not complete until all terminations are properly identified and labeled. Let's look at this process step by step.
Organize cable by destination.
- Know the wiring scheme. If you use incompatible parts for terminating, drastic results may occur. With copper IDC terminations, there are three predominant wiring schemes: T568A, T568B, and Universal Service Order Code (USOC). Only the T568A and T568B wiring schemes are compliant with the ANSI/TIA/EIA-568-A standard. (See Fig. 1, on this page).
- For work area terminations, make sure all cables are available and properly labeled at the wall outlet locations. In equipment rooms, make sure you install blocks and/or panels in accordance with the designer's layout.
- Verify the right products are on hand for the application. Modular furniture requires a different variety of outlets than drywall offices, so make sure you specify the product type and manufacturer.
Form and dress cable at the rear of the panel.
- First, prepare the cable for termination by bringing all cables into a bundle.
- On the front side of the rack, dedicate a minimum of one rack space (unit) [44.5 mm (1.75 in.)] of cable management for every two rack spaces (unit) [89 mm (3.5 in.)] of patch panels.
- Dress the cable by ensuring all cables are parallel to each other. Next, smooth them with your hand until they form a neat, orderly bundle.
- Cables may be entering the wiring closet from multiple directions, which frequently results in cables of many different lengths. After determining the proper amount of slack necessary, you should relabel the cables and cut them to uniform lengths. Pay attention to ensure the new labeling matches the old labeling.
- Use tie wraps or hook-and-loop straps to secure the cables. The tie wraps or hook-and-loop straps should be evenly spaced throughout the dressed length. Tighten tie wraps by hand only.
Use the proper cable management hardware.
- Several different types and styles of cable management hardware exist. All of these products are designed to properly support the in-place cables and relieve tension. They also provide support for additional cable you may need to install as a result of a move, add, or change. (See Fig. 2, on this page).
- Because UTP and Shielded Twisted Pair cable are protected from crosstalk and immunity from EMI through the cable's pair twist and lay configuration, make sure you maintain the minimum bend radius of the cable. This protects the integrity of the cable. The minimum bend radius for UTP and STP cable is four times the cable diameter, while optical fiber cable is 10 times the diameter.
COPPER IDC (PUNCH-DOWN) TERMINATION There are four basic types of IDC termination blocks used in the termination of horizontal and backbone copper cabling: the 66-type, 110-type, BIXTM, and LSA. These comprise the majority of the market; however, other devices are available. Several manufacturers provide rack-mountable and wall-mountable IDC termination hardware that can house multiple termination blocks.
To ensure a good connection, you must follow the IDC connecting hardware manufacturer's specifications closely. You also must comply with the proper procedures for:
- Determining the proper method and length of sheath removal.
- Untwisting the twisted-pair cable. (ANSI/TIA/EIA-568-A recommends a maximum of 13 mm [0.5 in.] of untwisted pairs, measured from the last twist to the IDC).
Each type of IDC termination requires you to use a specially designed terminating tool for performing the IDC termination correctly (See Fig. 3, on page 28). Several manufacturers market termination tools with interchangeable blades for use on several styles of IDC termination blocks. It's important to make sure the brand of tool you're using is compatible with the blade.
Sometimes different blades look similar, but there are slight differences in design. Improper matching of termination tool handle and blade can lead to serious personal injury, as well as poor terminations.
The following procedures generally address the proper methods and tools required to terminate copper cable on each type of IDC termination block.
1. Determine method and length of sheath removal. You can perform sheath removal three ways:
Ringing tool: The ringing tool contains a razor blade, set to a depth that allows you to slit the sheath deep enough to separate the sheath, but not nick the inner pairs. To properly use this tool, insert about 13 mm to 19 mm (0.5 in. to 0.75 in.) of the cable into the tool. Turn the tool and then remove the severed sheath with electrician snips.
Electrician's snips: Using the electrician's snips, carefully cut into the sheathing to a depth that exposes the rip-cord. Using the rip-cord, pull down the sheathing until you're ready to remove the proper length of sheath. Then remove the severed sheath with the snips.
Slitter tool: You should carefully insert the slitter tool between the cable sheath and the pairs. Slide the tool carefully down the sheathing until you've prepared the proper amount of sheathing for removal. Then, remove the severed sheath using snips.
2. Using a proper sheath removal tool, remove the cable sheath in accordance with ANSI/TIA/EIA-568-A standards and the termination equipment manufacturer's specifications.
- Remove only enough sheath necessary to terminate the cable pairs and ensure that the twist of the pairs is maintained. A common fallacy in the industry is that you should remove only 50 mm to 76 mm (2 in. to 3 in.) of sheath from the cable. This requirement can vary, depending on the block, type, and size of the cable as well as type of IDC termination hardware manufacturer.
3. Separate, identify and tie off binder groups.
- Binder groups are associated with 50-pair and larger pair-count cables.
- A unique color code identifies each binder group. Cables are grouped in 25-pair increments with each 25-pair group (or subgroup) individually wrapped with a fabric or plastic tape to identify the groupings. Depending upon manufacturer, 25-pair binder groups are combined into identifiable master groups. (See Table, on this page).
- Tie off binder groups to keep them identified until ready to terminate. One helpful hint is to use a copper pair of the same color as the binder group. Twist it snugly, but not tightly to both the sheath end and the outside end of the unsheathed cable binder group. This helps to identify binder groups.
4. Fan out and form cable pairs from each binder group.
- Place cable pairs uniformly so they do not cross or interfere with any other pairs.
- Wire pairs should be parallel with no tension at the point of connection and equal tension on all connections.
THE 66-TYPE TERMINATION BLOCK The 66-type IDC termination block is the choice for connecting voice applications such as PBX, Key Telephone Systems (KTS), and some LANs. Several manufacturers of 66-type termination block designs have updated their termination blocks to handle high-speed data applications and comply with ANSI/TIA/EIA-568-A Cat. 5 specifications. Make sure you're installing the appropriate 66-type IDC termination block in new installations. You typically mount the 66-type termination block on backboards with brackets.
THE 110-TYPE TERMINATION BLOCK Electrical professionals use the 110-type IDC termination hardware in both voice and data cabling applications. You'll find backbone cabling is commonly terminated on wall- or rack-mounted 110-type termination blocks in increments of 50, 100, or 300 pairs as well as on a 900-pair wall mount.
The majority of patch panels are wired in specific configurations (i.e.,T568A, T568B, USOC) and are mainly constructed with 110-type connectors.