Work areas and outlet density

The owner's project manager for Harborview sends a one-line request: two data jacks per desk. Roz reads it aloud to Daniel and asks what is missing. He starts a list. Clinic exam rooms do not have desks. Classrooms need outlets for projectors, lecterns and wall displays. Wireless access points need cabling in the ceiling. Cameras, card readers, nurse call stations, digital signs, printers and building controllers all need connections. By the end of the morning his list has nineteen outlet types, and the owner's one line has become a table. That table is what this lesson is about.

What a work area is

In cabling standards, a work area is the space where occupants use telecommunications equipment: an office, a cubicle, a classroom seat cluster, an exam room, a reception desk. The work area begins at the equipment outlet and includes the cords and equipment that plug into it. The horizontal cabling ends at the outlet, so anything on the work area side, such as a cord, adapter or desk-mounted switch, belongs to the user's equipment rather than to the cabling plant.

For planning, ANSI/TIA-569 uses a work area size of about 10 square meters (100 square feet) of usable floor space when the actual furniture layout is not yet known. Usable space excludes corridors, washrooms, shafts, mechanical rooms and stairs. A floor with 1,800 square meters of usable office space would therefore be planned for about 180 work areas. When the architect supplies a furniture plan, the designer counts real positions instead, and the planning figure becomes a check on whether the plan seems reasonable.

The minimum outlet count

ANSI/TIA-568.1 requires at least two equipment outlets per work area in a commercial building. Each outlet is served by its own 4-pair cable or fiber pair, run as a separate home run to the telecommunications room. At least one of the two must be balanced twisted pair, and the other may be twisted pair or fiber. Many owners specify more, because two outlets at a desk are quickly taken by a computer and a phone, and a docking station, a second computer or a desk camera then needs a third.

The minimum is a floor, not a design. Roz tells Daniel to think about outlet density in terms of devices, not desks. A modern work area may have a laptop on wireless, a desk phone that is really a softphone, two monitors that need no network at all and a docking station that does. The real question for each space is which devices need a wired connection there for the life of the cabling, including devices that do not exist yet.

Outlet types beyond the desk

Much of today's horizontal cabling serves devices that have nothing to do with desks. Wireless access points are the largest group in most buildings. Security cameras, access control readers, intercoms, digital signage, audiovisual equipment, point-of-sale terminals, building automation controllers, lighting control and occupancy sensors are others. ANSI/TIA-862 and the ISO/IEC 11801 part for distributed building services describe a coverage-area approach for these devices, with service outlets placed on a grid in the ceiling so that a device can be added anywhere near one. RCDD-114 covers the systems themselves; this lesson counts the cables they need.

Wireless access point grids

Because wireless designs change as devices change, many designers cable for access points on a regular grid rather than only at today's planned locations. TIA guidance for cabling to wireless access points describes a grid of cells about 18 meters (60 feet) on a side, with cabling to a point near the center of each cell and two Category 6A cables to each location. The wireless designer then places access points within reach of those outlets. When the wireless design is complete and the owner wants exact locations, the grid becomes a check that coverage will not run out as density rises.

Outlets in special environments

Some building types have their own standards for outlet counts. Health care facilities follow ANSI/TIA-1179, which recognizes that patient rooms, intensive care rooms and operating rooms need many more outlets than offices for monitors, pumps, nurse call, beds and clinical displays, and that clinical spaces need specific locations near beds and headwalls. Educational facilities follow ANSI/TIA-4966, which addresses classrooms, labs, lecture halls and dormitories. Residential buildings follow ANSI/TIA-570. Data centers follow ANSI/TIA-942, covered in RCDD-115. On a mixed-use building like Harborview, the clinic floors follow the health care guidance and the classroom floor follows the education guidance, while the offices follow the commercial building standard.

Regulators and owners may add requirements of their own. Clinical outlets may need to be on emergency power, and medical equipment may need outlets in particular places on a headwall. Classrooms may need outlets in the floor for flexible furniture. Accessible design rules in the ADA Standards for Accessible Design set the heights at which outlets and controls must be reachable. The designer must gather all of these before counting.

The outlet schedule

Roz's office turns the outlet list into an outlet schedule: a table that lists every room, its use, the number of each outlet type in it, and the media and category for each. The schedule is the bridge between the owner's needs and the drawings. It feeds the cable count for each telecommunications room, which in turn sizes the patch panels, switches, racks, pathways and power. It also gives the cost estimator the quantities for the bill of materials and the commissioning agent the list of links to test. On large projects the schedule lives in a spreadsheet or a design tool that generates the labels and the test plan automatically.

A good schedule records the reason for each outlet, not just the count. When a value engineering meeting asks which outlets can be cut to save money, the designer can show that a particular room's outlets come from a clinical standard, an accessibility rule or an owner requirement, and which ones are planned spares. Spares are not waste; lesson 11 explains why cutting them is usually false economy.

Outlet placement and mounting

Counting outlets is only half the work; placing them is the other half. Wall outlets are usually mounted at the same height as the power receptacles beside them, and both must meet the accessible reach ranges in the ADA Standards for Accessible Design and the building code adopted locally. Outlets for wall-mounted displays sit behind the display, often with a recessed box so that the plug does not push the screen away from the wall. Ceiling outlets for wireless access points and cameras are placed where the device will be mounted, with enough slack and a box or bracket that the device can be fixed to. Floor boxes serve desks in the middle of large rooms, and they must be coordinated with the structural engineer, because cutting a slab after it is poured is expensive and sometimes impossible.

Each outlet location also needs a pathway to it. A wall outlet needs a box and a conduit or open space in the stud cavity up to the ceiling; an outlet in a concrete or masonry wall needs a conduit set during construction. The cabling designer should mark every outlet type on the drawings with a symbol that the electrical contractor will recognize, because in many projects the electrical contractor installs the boxes and conduits even though the cabling contractor installs the cable. Missing boxes are one of the most common causes of delay and change orders on cabling projects.

Outlet faceplates have a limited number of ports, commonly one to six, and the designer chooses them by location. A classroom lectern with four outlets can use a single four-port plate; a desk with three outlets might use a four-port plate with one blank insert, leaving a spare position that a future cable can use without a new faceplate. Faceplates should carry the outlet identifiers described in lesson 12, printed rather than handwritten, so that a technician can find the matching port in the telecommunications room without a search.

Outlet counts should also be checked against the space that will hold their cables. A classroom with six outlets, two access point cables and a display needs nine cables through its door frame or ceiling, and a corridor serving twenty such rooms carries well over a hundred cables to the telecommunications room. The outlet schedule therefore feeds the pathway design directly, and a late increase in outlets can overfill a tray that was sized for the original count.

Daniel's outlet schedule for Harborview ends up with 1,412 horizontal cables across four floors, against the owner's original estimate of about 600 based on two jacks per desk. Roz takes the schedule to the next design meeting and walks the owner through each outlet type. The project manager approves it, adding that he wishes someone had shown him a table like this before the budget was set.