Cables and fables

Installing data cabling around an old office building can provide a contractor with all sorts of problems. Solid floors, null ceiling voids and masses of redundant cable are just a few. And to add insult to injury, in classified buildings, you’ll find they’ve not been designed to take cable runs. But finding a solution for the open-plan office environment needn’t be such a tough nut to crack. Especially if contractors take on board the right sort of advice at an early stage.

For instance, it may be necessary to provide voice and data outlets in central locations, which creates a specific set of problems. Structured cabling systems need not be limited by the more traditional “strapped to the walls” style of installation.

Depending on the size of the contract, you may have the luxury of a fully raised flooring system, which will considerably ease your burden. Or, you may have to make do with using whatever ceiling space you can get access to. Either way, you must adopt a professional solution for your installation.

When designing a cabling system, consider the products now available, that help to maximise the space available under the floor or in the ceiling void. Besides the widely used floor box, holding half a dozen voice or data outlets, there is also the MuTOA or Multi-User Telecommunications Outlet Assembly.

MuTOA magic

A MuTOA is a very versatile way of installing cables under a raised floor. It groups all the wall outlets together in one place. The patch lead, therefore, needs to be longer than the normally allotted 3 m. By running the cable group from the MuTOA out under the floor, you can exit from the floor void via a floor grommet or hive into the desk system. The standard work area group should be eight, up to a maximum of 12.

A patch lead up to 20 m long from the MuTOA can be used to connect directly to the desktop apparatus. Remember, as the patch lead length increases, the horizontal cable length decreases in direct proportion plus 20% to compensate for the additional increase in attenuation, due to the patch cord being made of stranded and not solid core cable.

The MuTOA must be securely fixed in a fully accessible area, preferably adjacent to the desk systems being wired, prior to each incoming line being terminated to its respective RJ 45 outlet. It must not be located in ceiling spaces, under access flooring, or in any obstructed area. And don’t install in office furniture or partitions that can or will be moved.

Probably the most significant benefit of MuTOAs is that open floor areas can be swiftly reconfigured by using the full length of the patch lead. This can be done by non-technical installation personnel who are already on site, since the only cabling requirement is to install the patch lead between the MuTOA and the desktop apparatus.

It should also comply with most manufacturers’ warranty programmes’ link tests with regards to moves and changes because the horizontal run from the equipment room to the MuTOA is not disconnected or repulled during relocations.

When laying cables in an underfloor space, it is always preferable to use cable basket to provide a secure platform to support the cables. Never be tempted to lay data cables directly onto the floor as this can lead to damage due to disturbance by other workers on site. Remember, this is valuable space and has to be shared with pipework and electrical installations, not to mention heating and ventilating ducting.

Another method of avoiding laying cables directly on the floor is to use “J” hooks, especially when installing with a raised floor or in the ceiling void. Under the floor, they are attached to the upright stays of the floor using a simple clip fastening and should be spaced at approximately 1·5 m intervals. The cable bundle is then placed in the “J” hook and secured, holding it safely off the floor.

There is a similar system for use in the ceiling void, but never lay cable across a suspended ceiling. It is a disaster waiting to happen.

On the whole, “J” hooks are an easy to use, and cheaper, alternative to cable basket, although they offer less overall protection.

Care should be taken to ensure that data cables are not laid in close proximity to power cables to avoid the problem of induced noise. As a general rule, avoid parallel runs of power and data cables unless there is a minimum gap of at least 150 mm. Even then, keep these runs to a minimum or use a metal shield separator. Never be tempted to take the easy option and use an existing electrical tray work as a platform for the data cables.

If you have to cross over power cables, do so at right angles and construct a simple bridge out of tray or basket, or use J hooks again to carry the data cables up and over.

Finally, it’s always a good idea to identify data cabling so that other contractors who follow on from you are aware of its presence. Tie a label to the cable runs stating “Data Cables”. These labels should be clearly readable and fixed in a prominent position at approximately every 3 m. There is no guarantee, but it may well prevent subsequent disturbance.