The following information is provided as-is and with no warranty, express or implied. You should consult the relevant building authorities, officials, and legal counsel for questions on these matters. If you take legal or building code advice from a random guy on Reddit, you're going to have a bad time
Structured Cabling, Plenums, and You: A brief guide to cabling in your buildings
Why are you writing this? Every now and then on /r/sysadmin, /r/networking, or /r/msp, there are questions about running cabling in your company's building or one of your customer's buildings. People ask what kind of cable to buy, can they run it next to this or that, and so on. This guide attempts to answer some legal and code questions and is not a how-to guide on running cable.
Who are you again? This guide will be written from the perspective of a contractor (me) operating in Florida, in the United States. I hold an Alarm Systems 1 Electrical Contractor license. In the state of Florida, this qualifies me to install ALL cabling inside and outside structures provided that that cabling does not carry more than 98 volts, as well as installation and maintenance of fire and burglar alarms. My MSP acquired this license so that we can legally run cabling for customers in addition to the IT Services we provide.
Before going any further, let me introduce the Prime Directive
The Prime Directive - Hire a properly qualified contractor
In almost all cases, cabling work should be done by a properly qualified contractor. Not everybody who will take your money is a properly qualified contractor.
How do I find a properly qualified contractor? First, get an idea of what you want done. Have your scope of work statement condensed down a few bullet points. Then, call your local government offices and explain that you want some work done and you need to know what license a prospective contractor will need. They will direct you to Code Enforcement, Building Inspections, Contractor Licensing, or some other similarly named department. Once you're on the phone with them, explain in brief the scope of work and ask what license would be required to do so. They will give you the information you need and how to verify a license.
Then, when you are seeking bids to do the work or you just start randomly Googling local companies and calling them, make sure they have the right license or a license that exceeds the requirements. The State of Florida maintains myfloridalicense.com where you can lookup license holders. Your state or locality might have a similar service.
I don't need no stinkin' contractor. I can do this myself!
Maybe. However, allow me to introduce you to the almighty power of "someone else's problem" (SEP).
Situation: You need 100 Ethernet cables installed for your new office.
Option1: You and your buddy do the installation
Option2: You follow The Prime Directive
Problem 1: The cabling is installed too close to 277volt lines which feed overhead lighting. Your VoIP phones crackle and hiss all the time
Option1: You and your buddy must cut and re-pull 100 cables via a different route to fix the problem
Option2: SEP!
Problem 2: The installed cabling is Copper-Clad Aluminum cabling that you got from Amazon for $90 a box and it's shit because CCA is shit and should never be installed
Option1: You and your buddy must cut and re-pull 100 cables using a different supplier to fix the problem
Option2: SEP!
Problem 3: An installer falls off a ladder and injures his back while leaning way over a ceiling tile to reach something. The ceiling grid takes major damage and he's out of work for awhile
Option1: Workers Compensation denies your claim and you have to do a shitton of appeals because your company does NOT carry insurance for that sort of thing
Option2: SEP!
Problem 4: The Fire Marshall comes in to inspect something else and notices a bundle of ethernet cables that weren't there before. He checks the label and finds out that they aren't plenum-rated and they should be. He demands that these cables be replaced immediately and threatens to revoke your Certificate of Occupancy until it's done.
Option1: You get to explain to your boss how you shut down the company for a month to save some money because you don't understand code
Option2: SEP!
I hope I've made my point. Just because it's "just low voltage" doesn't mean that code doesn't apply. The United States National Electrical Code (NEC, NFPA 70) has huuuuuuge sections that dictate the running of low voltage cabling, fiber optics, etc.
"Okay, so are you saying I need a license just to plugin a printer to an Ethernet cable?!"
No, I'm not. Here is a GENERAL rule of thumb (see italicized bit at the start of this post) for whether you need a license:
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Does the cable run start AND finish in the same room?
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Can you SEE the entire cable run from start to finish while standing in a normally-occupied space WITHOUT using any special tools? If a cable is tucked behind a desk or a file cabinet, that's fine
If the answer to both of those is yes, then you probably do not require a license to install or modify it. If you're not sure, Prime Directive. The Building Code people will tell you. It's literally their job.
"Right, so what's all this business about Plenum spaces?"
When people ask on here about plenum-rated cabling, it always makes me nervous. Because if you are talking about running plenum v. non-plenum cabling (CMP vs CMR/CM) then you're talking about a scope of work that would require a license to do, at least where I operate. In which case you shouldn't be asking Reddit, you should be following the Prime Directive. If you ARE licensed to do that kind of work... you should KNOW the answer and not be asking on Reddit.
That said, Plenum-rated cabling (CMP) is required when cabling is being run in a "plenum space". A Plenum Space is a space that is used for return air back to the building's air conditioning or heating system. Plenum-rated cabling has an outer jacket that, if exposed to extreme heat or open flame, will not release toxic gasses. You can see how this would be VeryBad™ if you have toxic gasses being pumped all over the building by your air conditioning or heating system. Most commonly, a Plenum Space is the area above ceiling tiles or below a false floor IF that is being used as an air return space.
Just because it's above ceiling tiles does not necessarily mean it's a plenum space, though it might be If you have a question, then PRIME DIRECTIVE
If your building has ducted returns for the HVAC system, then the area above the ceiling tiles is likely NOT a plenum space. If your building does NOT have ducted returns for the HVAC system, then the area above the ceiling tiles MIGHT be a plenum space.
Plenum Space - Plenum-rated cable required
Not a Plenum Space - Plenum-rated cabling permitted, but not required
"So what if I just buy and run plenum-rated cabling everywhere? I can do that right?"
Yes, you can. However nobody likes doing this for two reasons.
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Plenum-rated cabling is between 1.5 and 3 times more expensive than non-plenum rated cable.
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Plenum-rated cabling is ASS to work with. It seriously sucks. It's stiff, it hates turning corners, it usually requires more feed-points for longer runs, its outer jacket cracks easier if you bend it too far. It's just ass. Nobody likes it. We only use it when we have no other choice.
We dislike it so much that usually we'll redraw plans to avoid plenum spaces, if possible. If we're just passing through a plenum space from one floor to another, we'll install (or have the Sparkies install) a bigass set of 2 or 4 inch EMT conduits with proper fire-stop to allow our wiring to pass through the space. That way we don't have to use Plenum-rated. This may differ in your jurisdiction. Some areas require plenum-rated cabling even if it's inside conduit if that conduit passes through a plenum space. And some places like highly sensitive medical facilities require plenum-rated cabling everywhere because of REASONS. So, if you have a question then PRIME DIRECTIVE.
"Something you said here isn't accurate. In MY jurisdiction, we're allowed to do X Y or Z..."
You're probably right. I assume you followed the Prime Directive , in which case, knock yourself out!
"This doesn't apply to fiber-optic cables right? They don't carry voltage, after all!"
Sorry, NEC goes BRRRRRRRR. Article 770 of the National Electrical Code (NEC, NFPA70) governs the installation of Fiber optic cabling. Yes, you still need to be licensed in my jurisdiction to install it.
Thank you for reading this brief guide on code and plenums. I will add / edit sections over time as I think of stuff.
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