Connectors, outlets and work areas

Every structured cabling channel is a chain of cable and connections, and the connections are where most of the performance is won or lost. A Category 6A cable run perfectly through the ceiling will fail if it ends on a Category 5e jack, or on the right jack with the pairs untwisted too far. This lesson covers the connecting hardware of the horizontal: the modular jack and plug, the two wiring schemes, patch panels and punch-down blocks, outlets and faceplates, and the cords that complete the channel at each end. It also covers the work area itself, where the cabling meets its users. The hands-on skills of terminating jacks and panels are taught in LVT-130; this lesson explains what the hardware is and how it is chosen.

The eight-position modular connector

The connector at the end of almost every horizontal channel is the eight-position, eight-contact modular jack and plug, commonly called RJ45. Strictly, RJ45 is an old telephone industry designation for a particular wiring of that connector, and the standards call it an eight-position modular connector, but the informal name is universal. The jack has eight spring contacts in a row, numbered 1 to 8 from left to right when viewed from the front with the latch slot down, and on the back it has insulation displacement contacts into which the cable's eight conductors are pressed. Higher-category jacks are built with small compensating circuits on their internal boards that cancel the crosstalk created inside the plug, which is why jacks are matched to a category and, on warranted systems, to the manufacturer's cable.

The plug is crimped onto stranded cords in a factory. Field-terminated plugs, used for modular plug terminated links to cameras and access points, are made for solid horizontal cable and must be the type specified for that use. Factory-made cords are preferred everywhere else, because their performance is tested and consistent.

T568A and T568B

The four pairs of a cable are identified by color: blue, orange, green and brown, each with a solid-colored conductor and a white conductor striped with that color. TIA-568 defines two ways to assign the pairs to the eight jack positions, called T568A and T568B. Both keep each pair on two positions that the equipment expects to be a pair, and both perform identically. The only difference is that the orange and green pairs swap places.

What matters is consistency. Both ends of a horizontal link must be terminated to the same scheme; a link with T568A at one end and T568B at the other is a crossed link that will fail a wiremap test. TIA-568 lists T568A as the preferred scheme, and many Canadian and US government and institutional specifications require it, while T568B is widely used in commercial work by long habit. Most jacks are printed with color codes for both schemes, which is convenient and also how mistakes happen: an installer reading the wrong row of colors terminates one end to the other scheme. Cobalt Line marks the scheme for each job on its work orders, and Dev checks the first few jacks a new apprentice terminates at both ends.

Cords are wired straight through: position 1 at one end to position 1 at the other, and so on. Crossover cords, which swapped pairs to connect two similar devices directly, are no longer needed because modern equipment detects and corrects the crossover automatically.

# Wiremap check: compare the far-end positions of a link with what each scheme expects
A = ["white-green", "green", "white-orange", "blue", "white-blue", "orange", "white-brown", "brown"]
B = ["white-orange", "orange", "white-green", "blue", "white-blue", "green", "white-brown", "brown"]

def wiremap(near, far):
    # for each near-end position, where does the same conductor land at the far end?
    return [far.index(color) + 1 for color in near]

links = {"2B-A01 (A to A)": (A, A), "2B-A02 (A to B)": (A, B),
         "2B-A03 (pair 1 reversed)": (A, A[:3] + ["white-blue", "blue"] + A[5:])}
for name, (near, far) in links.items():
    m = wiremap(near, far)
    result = "pass" if m == list(range(1, 9)) else "fail"
    print(f"{name:26} far-end positions {m}  {result}")

2B-A01 (A to A)            far-end positions [1, 2, 3, 4, 5, 6, 7, 8]  pass
2B-A02 (A to B)            far-end positions [3, 6, 1, 4, 5, 2, 7, 8]  fail
2B-A03 (pair 1 reversed)   far-end positions [1, 2, 3, 5, 4, 6, 7, 8]  fail

The second link shows the classic crossed pairs: the green and orange pairs land on each other's positions, 1-2 swapped with 3-6. The third shows a reversed pair, the two conductors of pair 1 swapped, which a tester also reports. LVT-130 shows the other wiremap faults: opens, shorts and split pairs, the last of which a simple continuity tester cannot see.

Patch panels and punch-down blocks

In the telecommunications room, the horizontal cables terminate on patch panels: rows of jacks in a rack-mounted frame, usually 24 ports per rack unit. Panels may be flat, with all ports in a straight row, or angled, which lets cords route directly to the vertical cable managers without horizontal managers. Some panels use individual snap-in jack modules, often called keystone style, so that a damaged jack can be replaced alone; others have jacks built into a printed circuit board in groups of six or more. High-density panels fit 48 ports in one unit but need thinner cords and careful cord management. Shielded panels have a metal frame with a bonding point and must be used with shielded jacks.

Voice backbone and some low-speed circuits still terminate on punch-down blocks. The 110 block, a plastic block with rows of insulation displacement slots, is the current standard and is rated for Category 5e and higher in its better versions. The older 66 block, a metal-clip block once common for telephones, is rated only for voice. Cross-connect wires, called jumpers, are punched between blocks to connect backbone pairs to the horizontal pairs serving an analog line.

Outlets, faceplates and boxes

At the work area, the cable ends in a jack mounted in a faceplate. Faceplates hold from one to six or more jacks and fit standard electrical device boxes or low-voltage mounting brackets, which are open rings that attach to the wall board without a full box. Surface-mount boxes are used on block walls, on ceiling grids for wireless access points and wherever a cable cannot be concealed. Floor boxes and poke-through devices serve desks in open areas away from walls, and modular furniture has its own outlet openings with adapter plates.

Mounting heights are set by the drawings and by the accessibility provisions of the building code. A typical office outlet is centered about 18 in above the floor, beside an electrical receptacle, with wall telephone outlets higher. Outlets for wall-mounted displays, card readers, intercoms and wall access points are mounted at the heights the device requires. Each faceplate is labeled with the identifiers of its jacks, in the format covered in Lesson 10, and many owners use colored jack inserts or icons to show the system: blue for data, for example, and a different color for the security network or building systems.

Hospitals show how specialized outlet requirements can become. At St. Brendan's, each patient room has outlets in the headwall behind the bed for the nurse call and patient monitoring systems, at the caregiver workstation, on the wall opposite the bed for the television and patient entertainment system, and in the ceiling for a wireless access point, with counts and locations set by the hospital's standard and by TIA-1179's guidance for healthcare. The outlets in the headwall are mounted in the manufacturer's headwall unit, among medical gas outlets and electrical receptacles, and Maya learns to coordinate their positions with the headwall supplier before rough-in.

Cords and the work area

Cords complete the channel. Patch cords connect panel ports to each other in a cross-connect; equipment cords connect panels to switches; work area cords connect outlets to devices. All of them must be of the same category as the installed cabling, factory-made and tested, and of the right length: long enough to route neatly through the cable managers, short enough to avoid tangles and to stay within the 10 m cord allowance. A cord that is too long ends up coiled in a cable manager or on the floor, and a cord that is too short pulls on the jack.

Cords are the weakest part of any channel because they are handled every day. They are crushed by chair casters, bent sharply behind desks and pulled out by the cable instead of the plug. A failing cord is the most common cause of a desk losing its connection, and the first thing Dev checks on a service call. That is also why the horizontal cabling is tested as a permanent link without cords: the contractor guarantees the permanent part, and the cords are replaceable.

Choosing connecting hardware

On a warranted job, connecting hardware is chosen by the manufacturer's system, not piece by piece. Sanjay specifies one product line of jacks, panels and cords matched to the cable, and the warranty registration lists them. Within that line, he chooses the details that suit the job: angled panels where rack space is tight and vertical managers are generous, keystone-style panels where jacks may need individual replacement, tool-less jacks for crews terminating large numbers quickly, shuttered jacks in dusty spaces and jacks in colors that match the owner's system color scheme. For devices in the ceiling, he chooses between a surface-mount box with a jack and a field-terminated plug, following the owner's preference and the test method the warranty accepts.

Outlets in special environments need special hardware. Outlets in kitchens, washrooms and outdoor locations need covers or sealed jacks; outlets in hospital patient areas may need antimicrobial faceplates that tolerate cleaning chemicals; and outlets in industrial spaces may need ruggedized connectors with sealing gaskets. Each still terminates the same four-pair cable to the same wiring scheme.

Before any jack is terminated on a job, Dev has the crew agree on three things written on the work order: the wiring scheme, the product line and the label format. Problems with any of the three are cheap to prevent and expensive to fix after a few hundred jacks are installed.