Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm looking for some useful information about how to design network cabling for a building.

I'm not so much interested in wiring standards such as 568A, but more interested in physically wiring the building.

For example:

Is it better to have all the cabling from all the data points in a building to go back to a central point (where line length permits), or is it better to have a number of local switches linked back to a core switch or router via fibre (or copper) links?

Any useful tips or URLs would be appreciated.

share|improve this question
The best answers will vary based on the size of the building in question. About how many rooms will be wired, what is the density (cube farms, dedicated offices, cramped call center?), and what are the physical dimensions? – mhud Aug 10 '09 at 18:34
Whilst I do have a specific building in mind, I was avoiding the temptation of giving specific details, as I was hoping for some pretty generic advice. If generic advise is not really practical, then the building in question is basically a two storey building, split into six separate units. Each unit being a large open plan space (18m x 10m), some of the units might be sub-divided into individual offices, unfortunately this isn't known at the moment. Each unit will initially need a minimum of 24 data points, but I'd like it to be extendible up to 96 data points per unit. – Bryan Aug 10 '09 at 18:46
What mhud said. There are a myriad of ways to do this, and if you aren't licensed in low-voltage wiring in your locality and don't have experience doing it, you probably shouldn't be doing the nuts and bolts without professional guidance. – Karl Katzke Aug 10 '09 at 18:47
The building also has a dedicated server room, and a few other small rooms / coridoors that will probably have a data point or two for printers and other devices. – Bryan Aug 10 '09 at 18:48
Wiring expertise isn't the issue, we have engineers that have cabled up many a small business (both copper and fibre), however this building is a larger project that requires a degree of planning, rather than just running a ream of cables around a room to a small server room. – Bryan Aug 10 '09 at 18:52
up vote 12 down vote accepted

The short answer re: how much cable to run and where to run it is: It DependsTM.

I like having as few wiring closets as possible, with either copper or fiber risers interconnecting the wiring closets (more runs than you think you'll ever need), and minimizing the number of overall Ethernet switches.. Unless you have some compelling need for more Ethernet switches you typically don't "save" a anything by running fewer long runs from a closet to an area and then "fanning out" from a "workgroup" switch with patch cables, etc. You end up with an unmaintainable mess (power cords kicked out, switches with junk stacked on them by users, etc).

I try to stay away from fiber unless I have a compelling reason (distance, electromagnetic noise, environmentals too harsh for copper, privacy concerns). Multiple copper runs aggregated together can deliver multiple Gb/sec more cheaply, today, than 10G on fiber (both because of the expense of the fiber versus copper cable, and because of the cost of the electronics on the end).

re: running and planning the physical cable plant, an almost verbatim theft from an earlier answer of mine applies:

If you're willing to spend a little money, you can get the "bible" for cabling installers: The "Information Transport Systems Installation Methods Manual" from BICSI. It's $129.00, but it's got an unbelievable amount of detailed information.

  • Run more cable than you think you're going to need. The wire is cheap, the installation labor is not.
  • Use well-labeled wall plates with some kind of documented labeling standard. It shouldn't be complicated, but it should be documented.
  • If you can, create an as-built drawing. It will help you (or the next guy) when problems come up.
  • No matter where you put wall plates, users will put bookcases, desks, 1000 pound safes, etc, in front of them. Try and get in touch with the office space-planning people to see where good wall-plate locations would be.
  • If you're still using traditional non-IP telephones, coordinate with your voice vendor to run a single cable plant for everything if you are able. You can plug RJ-11 jacks into RJ-45 wall plates. Some people say that it's not a good thing to do, but I've seen it done for years w/ no ill effects.
  • Run more cable than you think you're going to need. >smile< Having to put switches in offices because you add IP phones, network-printers, and an Ethernet-attached camera where you thought that only a PC was going to be located is no fun.

If you're worried about legal compliance, check with your local electrical or building inspector. Most states don't classify "low voltage data cable" under electrical inspection guidelines, but you may have fire inspection-releated concerns.

share|improve this answer
I'd add to that "run at least two cables per office", because they might need it, and it's a lot cheaper to just run the jacks and wall plates once. – Bill Weiss Aug 10 '09 at 21:12
One caveat about bundled copper - you will almost never get 100% utilisation from a port-channel (be it LACP or PAgP), as the hashing algorithms used are per flow, not per packet. With a single 10G physical interface, you will actually be able to put 10Gb on the wire. – Murali Suriar Aug 11 '09 at 13:33
@Murali: The cost-to-performance ratio of a few bonded 1Gb ports will be better, today, than a 10Gb port. As soon as 10Gb becomes commodify that won't be true anymore (but, by that time, we'll be bonding multiple 10Gb ports together... >smile<) – Evan Anderson Aug 11 '09 at 13:40
  1. In the United States (not sure about UK, but knowing y'all's laws...), before tackling a cabling project, you should probably have your low voltage license unless the job cost is below $1000. There are exemptions in some areas, but be aware that you might be on the handle for fines for not complying with laws.
  2. If you're not familiar with how to do a large scale infrastructure project like this, then you shouldn't be doing it.
  3. The answer to your questions not only depends on what kind of building, but what kind of infrastructure you're dealing with that's already in place. For example: What kind of conduit is run between the floors? Where is the datacenter? How long will the runs be? How tight are the bends in any conduit? (Under the minimum fiber optic bend radius?) How close to electrical mains is your server room and/or the conduits that the data lines will be traversing? How many ports are we talking and how many hosts? What are their bandwidth needs? What's the intended topology of the network? Are you going to have voice (VOIP) lines run along with the data or will they be sharing a network?

In short: There's a reason that people who do this stuff get paid. Seek a professional.

share|improve this answer
Thanks Karl, you are quite right, however, for info, the company I work for is a rapidly expanding small IT company. Whilst we don't usually get involved in cabling projects, (we tend to maintain the devices on the end of the cables instead), but it's inevitable that this is the kind of job we are going to pick up more and more, hence the reason why I was asking for generic advise rather than site specific details. The installers we have are time served and trained, but they aren't planners, they are installers. – Bryan Aug 10 '09 at 19:07
Bryan, that's what consultants are for! Get one in to teach y'all what variables to take into account. Some of them are highly variable and will depend on the length of the runs you're dealing with... – Karl Katzke Aug 10 '09 at 20:03

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.