One of the early decisions you must make when planning your network is where to place the wiring closet(s), - since this will be where you will have to install many of the networking cables and networking devices. (Note: Detailed examples and practice for wiring closets are provided.) The most important decision is the selection of the Main Distribution Facility/Facilities (MDF). There are standards governing MDFs and IDFs, and you will learn some of these standards while learning how to select the network wiring closet(s). If possible, tour your own school's (or one of your local business') MDF/IDF.

Finally, you will learn how to plan your network so that you can avoid some of the problems related to negative effects on networks caused by AC electricity from the power company. 

TIA/EIA-568-A specifies that, in an Ethernet LAN, the horizontal cabling runs must be attached to a central point in a star topology. The central point is the wiring closet, and is where the patch panel and the hub must be installed. The wiring closet must be large enough to accommodate all of the equipment and wiring that will be placed in it, and include extra space to accommodate any future growth. Naturally, the size of the closet will vary with the size of the LAN, and the types of equipment required to operate it. A small LAN needs only a space the size of a large filing cabinet, while a massive LAN requires a whole room.

TIA/EIA-569 specifies that each floor must have a minimum of one wiring closet and that additional wiring closets should be provided for each 1,000 m², when the area of the floor that is served exceeds 1,000 m², or the horizontal cabling distance exceeds 90 m.

Any location that you select for a wiring closet must satisfy certain environmental requirements that include, but are not limited to, power supply and heating/ventilation/air conditioning (HVAC) issues. In addition, the location must be secure from unauthorized access, and must meet all applicable building and safety codes.

Any room, or closet that you choose to serve as a wiring closet should adhere to guidelines governing such items as the following:

• materials for walls, floors, and ceilings
• temperature and humidity
• locations and types of lighting
• power outlets
• room and equipment access
• cable access and support

If there is only one wiring closet in a building, or if the wiring closet serves as the MDF, then the floor on which it is located must be able to bear the load specified by the installation instructions included with the required equipment, with a minimum capability of 4.8 kPA (100 lb/ft²). Where the wiring closet serves as an IDF, the floor must be able to bear a minimum load of 2.4 kPA (50 lb/ft²). Whenever possible, the room should have a raised floor, in order to accommodate incoming horizontal cables that run from the work areas. If this is not possible, then it should have a 30.5 cm ladder rack installed in a configuration designed to support all proposed equipment and cable. Floor coverings should be tile, or some other type of finished surface. This helps control dust, and shields equipment from static electricity.

A minimum of two walls should be covered with 20mm A-C plywood that is at least 2.4m high. If the wiring closet serves as the MDF for the building, then the telephone point of presence (POP), may be located inside the room. In such a case, the interior walls of the POP site, behind the PBX, should be covered from floor to ceiling with 20mm plywood, with minimum of 4.6 m of wall space provided for the terminations and related equipment. In addition, fire prevention materials that meet all applicable codes (e.g. fire-rated plywood, fire-retardant paint on all interior walls, etc.) should be used in the construction of the wiring closet. Rooms must not have a dropped, or false, ceiling. Failure to observe this specification could result in an insecure facility, allowing possible unauthorized access.

The wiring closet should include sufficient HVAC to maintain a room temperature of approximately 21° C, when all LAN equipment is in full operation. There should be no water or steam pipes running through or above the room, with the exception of a sprinkler system, which may be required by local fire codes. Relative humidity should be maintained at a level between 30%-50%. Failure to adhere to these particular specifications could result in serious corrosion of the copper wires that are contained within the UTP and STP. Such corrosion would deter efficient functioning of the network.

If there is only one wiring closet in a building, or if the closet serves as the MDF, it should have a minimum of two dedicated, non-switched, AC duplex electrical outlet receptacles, each on separate circuits. It should also have at least one duplex power outlet positioned every 1.8 m along each wall of the room, and should be positioned 150 mm above the floor. A wall switch, that controls the room’s main lighting, should be placed immediately inside the door.

While florescent lighting should be avoided for cable pathways because of the outside interference that it generates, it can be used in wiring closets with proper installation. Lighting requirements for a telecommunications closet specify a minimum of 500 lx (brightness of light equal to 50 foot candles), and that light fixtures be mounted a minimum of 2.6 m above the floor.

The door of a wiring closet should be at least .9 m wide, and should swing open out of the room, thus ensuring an easy exit for workers. The lock should be located on the outside of the door, but allow anyone who is on the inside to exit at any time.

A wiring hub and patch panel may be mounted to a wall with a hinged wall bracket, or with a distribution rack. If the choice is a hinged wall bracket, the bracket must be attached to the plywood that covers the underlying wall surface. The purpose of the hinge is to allow the assembly to swing out so that workers and repairmen can easily access the back side of the wall. Care must be taken, however, to allow 48 cm for the panel to swing out from the wall.

If the choice is a distribution rack, then it must have a minimum 15.2 cm of wall clearance for the equipment, plus another 30.5-45.5 cm for physical access by workmen and repairmen. A 55.9 cm floor plate, used to mount the distribution rack, will provide stability, and will determine the minimum distance for its final position.

If the patch panel, hub and other equipment are mounted in a full equipment cabinet, they require at least 76.2 cm of clearance in front, in order for the door to swing open. Typically, such equipment cabinets are 1.8 m high x .74 m wide x .66 m deep.

If a wiring closet serves as an MDF, all cable running from it - to IDFs, computers, and communications rooms on other floors of the same building - should be protected by 10.2 cm conduit or sleeved core. Likewise, all such cable running into the IDFs should be run through the same 10.2 cm conduit or sleeved cores. The exact amount of conduit that is required is determined by the amount of fiber optic, UTP, and STP cable that must be supported in each wiring closet, computer, or communications room. Care should be taken to include additional lengths of conduit in order to provide for future growth. To meet this specification, a minimum of two excess sleeved cores or conduits should be kept in each wiring closet. Where construction permits, all conduit and sleeved core should be kept to within 15.2 cm of the walls.

All horizontal cabling that runs from work areas to a wiring closet should be run under a raised floor. When this is not possible, the cabling should be run through 10.2 cm sleeves that are placed above door level. In order to ensure proper support, the cable should run from the sleeve directly onto a 30.5 cm ladder rack in the room. When used in this manner, to support cable, the ladder rack should be installed in a configuration which supports the equipment layout.

Finally, any wall/ceiling openings that provide access for the conduit, or sleeved core, must be sealed with smoke and flame-retardant materials that meet all applicable codes