Open office cabling: consolidation points and multi-user outlets

The second floor of Harbourview is planned as an open office for the college's administration, with rows of benching desks, a few glass meeting rooms and furniture that the facilities manager says will be rearranged at least twice in the first five years. She asks Roz a fair question: if the desks move, do the cables have to be pulled again? In a traditional design the answer is often yes, because each cable runs from the telecommunications room to a fixed outlet that may end up under a filing cabinet. Open office cabling is the set of design tools that let horizontal cabling adapt to moving furniture without being replaced.

The problem with fixed outlets in open offices

Horizontal cabling is meant to be permanent, but open office furniture is not. When workstations move, fixed outlets end up in the wrong places, and the usual fixes are bad ones: long work area cords snaking across the floor, cords run through furniture never designed for them, or new cables pulled into a crowded ceiling while old ones are abandoned. Abandoned cable is a real problem. It adds fire load, blocks pathways and, under the Canadian Electrical Code and many fire codes, may have to be removed. Designers therefore want a way to separate the permanent part of the cabling from the part that follows the furniture.

The standards give two tools for this, both permitted by ANSI/TIA-568.1 and described in ISO/IEC 11801 in similar terms: the consolidation point and the multi-user telecommunications outlet assembly, usually shortened to MUTOA. Both place an intermediate point in the open office so that the long, permanent part of each run can stay where it is while the short part near the furniture changes.

The consolidation point

A consolidation point is an interconnection point within the horizontal cabling, between the horizontal cross-connect and the equipment outlet. The permanent cable runs from the telecommunications room to the consolidation point, usually in a zone enclosure in the ceiling, under a raised floor or on a building column. A shorter cable then runs from the consolidation point to the outlet at the furniture. When the furniture moves, only the short cable is moved or replaced; the long run back to the room stays in place.

The standards set several rules for consolidation points. There may be only one consolidation point in any horizontal link. It must be an interconnection, with cable from each side terminated on connecting hardware, never a cross-connect with patch cords. It should be at least 15 metres from the telecommunications room, because closely spaced connections near the room can add crosstalk and return loss problems at high frequencies. It should serve no more than 12 work areas, so that one enclosure does not concentrate too many links. And it must be in a permanent, accessible location, not inside movable furniture and not hidden above a fixed ceiling with no access.

The cable from the consolidation point to the outlet is part of the permanent link, not a cord. That means the total length from the room to the outlet, through the consolidation point, is still limited to 90 metres, and it is tested as one permanent link. Consolidation point hardware must also be at least the same category as the rest of the link.

The multi-user telecommunications outlet assembly

A MUTOA takes a different approach. Instead of extending the permanent cabling to outlets at each desk, it ends the horizontal cabling at a group of outlets in a single fixed location, such as a column or a wall near a cluster of desks. Users then connect to the MUTOA with longer work area cords, routed through the furniture, that can be changed whenever the desks move. The horizontal cabling never changes at all.

Because the work area cords are longer than usual, the channel needs a different length budget. Cords use stranded conductors, which have higher insertion loss than the solid conductors in horizontal cable, so each metre of cord counts for more than a metre of cable. ANSI/TIA-568.1 therefore gives a formula for the maximum combined cord length when the horizontal cable is shorter than 90 metres:

Here C is the maximum combined length of the work area cord, the equipment cord and any patch cords, H is the length of the horizontal cable, and D is a de-rating factor for the cord type: 0.2 for 24 AWG cords and 0.5 for 26 AWG cords. The work area cord alone may then be W = C − T, where T is the length of the cords in the telecommunications room, usually taken as 5 metres. For 24 AWG cords, the work area cord may be no longer than 22 metres; for 26 AWG cords, no longer than 17 metres.

A MUTOA also follows the 12-work-area limit, must be in a permanent location such as a column or wall rather than in the ceiling or in furniture, and must be labelled so that each cord can be traced to its work area. Each cord should be labelled at both ends with the work area it serves, and the MUTOA should show the maximum allowed cord length.

Choosing between them

Both tools serve the same goal, but they suit different situations. A consolidation point is better when desks have outlets in the furniture and the users expect a normal short cord at each desk. It puts the flexible part of the system in the cabling contractor's hands: moving a desk means a planned move of a short cable. A MUTOA is better when furniture moves very often or when the owner wants users or facilities staff to make changes without a cabling contractor, because a cord can be unplugged and rerouted by anyone. Its drawback is long cords in furniture, which must be managed carefully to avoid damage and clutter.

Zone cabling is the broader approach of which consolidation points are one part. In a zone design, the floor is divided into zones of a few hundred square metres, each with an enclosure that serves every outlet type in the zone: desks, wireless, cameras and building systems. The zone enclosure can be a consolidation point, a MUTOA, or for building systems a place where service outlets are clustered. The same idea appears in ceiling-mounted enclosures for wireless and in floor boxes in raised-floor offices.

Furniture coordination

Open office cabling succeeds or fails on coordination with the furniture supplier. Systems furniture often has raceways in the base, the beam or the spine where cables can run between desks, with knockouts for outlets. The cabling designer needs the furniture drawings early to know where those raceways are, how much cable they can hold and whether they separate power from communications cables, because many furniture raceways have separate channels for each. Running communications cable in the same compartment as power cable is a code problem and an interference problem.

The point where cables enter the furniture is often the weakest part of the design. A cable that drops from a ceiling consolidation point to a desk usually needs a service pole or a power and data pole, which must be placed where it does not block movement or sightlines. Cables that enter from a floor box need grommets and strain relief. In each case, the designer should specify the entry method and show it on the drawings, and the furniture installer and cabling installer should agree on who supplies and installs each part.

Finally, the moves themselves need a process. The facilities team should have a simple procedure for a desk move: record the old and new locations, move or replace the short cable or cord, update the records and test the link. Without that procedure, the open office tools that were meant to keep the cabling tidy can produce a new kind of mess, with undocumented cords and abandoned short cables in the ceiling.

On Harbourview, Daniel and Roz choose consolidation points for the administration floor, with six zone enclosures in the ceiling, each serving up to ten desks and the wireless and camera outlets nearby. The facilities manager is pleased that a desk move will mean replacing a few short cables, not pulling new runs from the room. For the college's flexible project room, where tables move every week, they specify a MUTOA on each of two columns.