Hi guys. I have been googling for the past hour trying to find some information on low voltage requirements pertaining to commercial work.
99.9% of my commercial work is retro, and I am about to start working up a quote for a new building. Well, it's not new, the exterior is existing, the interior will be new.
It got me to thinking about the requirements for voice/data/audio cabling. For instance, wood structure vs. metal structure.
I understand that speakers need to be in cans, but what other requirements are there? EMT for instance? I do allot of retro data and voice cabling in schools, I always use emt conduit and/or fireblock when going thru walls or between floors.
Thanks all...

Plenum rating?

Hi Fred. I understand plenum vs. riser. I guess to be more specific, I am refering to the use of conduit. Using standard open back low voltage boxes vs. closed boxes.
When EMT conduit has to be used.
Are there any NEC standards that reference commercial low voltage wiring?

You need to find out what NEC codes (year) your local inspector uses. Some cities are many years behind the current NEC codes.

By the way Fred, Dave B. is an awesome guy to work with....

Thanks T.C.
I am wondering about current code requirements.

I have an example for you. A couple of months ago I had an electrician tell me that low voltage wiring can no longer be sitting on a drop ceiling. It must be tied up off the ceiling.
Last week I watched an electrician run romex in a suspended ceiling, and lay it on the ceiling tiles.
No, I didn't say anything :)
Is low voltage wiring really that free so far as where we run, and how we run our cabling?
By the way, most of the time, I secure my wiring above the tiles. I do this because I spend allot of time cursing people who don't, when I'm trying to put a ceiling tile back into place, and fire alarm wire keeps popping out.

Each state has its own reuirements as far as what is required. You must find out what is required in your area.

Most low voltage companies never read the NEC or do their jobs by the book. Many states dont even require low voltage to be inspected.

A good place for information is the Mike Holt website which also includes a forum which addresses low voltage.

Any specific advice you receive here is useless until you know what is required in your state. Many counties and cities within a state also tack on their own unique code requirements. What state are you in ?????

Here's some general items for considerations that I've learned through osmosis. Of course some items may be different based on your AHJ but I've found these to be rather universal...

1) speakers need not be in boxes unless ceiling is plenum rated i.e. the air return is non-ducted.
2) All freewire or LV cabling must be off the ceiling tile and grid. This is mainly to prevent chafing and snags on the grids sharp edges (shorts).
3) Plenum rated cable is needed for freewiring in plenum rated ceilings only. To simplify, plenum rated cable does not give off noxious fumes when exposed to fire and has a slower burn rate. you can use CL rated cable in plenum ceilings as long as it's in conduit.
4)all drops down the wall must be in rigid conduit and terminate in a box. Which is bitch because getting a VC in box sucks. Use depp back boxes for everything. Use a grommet where the free wire goes into the conduit.
5) We usually wrte the spec so conduit is "by others" that way we can just show up and fly, plus the EC can do it cheaper.
6) If the client wants to save money, frequently we'll pull the wire and hang loops above the drop locations and sell the job as a prewire only "for future use". Then after CO we'll come in and drop all the wires down the wall freewired so the owner can avoid all the additional conduit costs. Generally we only do this for video and audio runs. Telco and data is different, it has to be there.

My .02

Brian @ Connect Source

We just did 27 data drops in an office/commercial building. I was battling some of the same issues. A lot of the existing drops WERE in rigid conduit, and closed back boxes. BUT, where they wanted NEW drops, they already had LV boxes (no back) and no conduit installed. They had pulls strings all ready for us to pull the drops. So, we used they boxes and no conduit that they provided. Hopefully we'll be ok.

Don't forget fire rating, most fire districts will not allow two boxes in the same wall cavity back to back unless you wrap the box in fire putty.

This is the stuff I'm talking about....
briremo, thanks for your list.
idodishez, I've found myself in similar situations. Doing work, and crossing my fingers.
That's why I'm asking this question.
cma, that's not one that I was aware of.
Thanks guys. Anyone else have anything to add?

Whenever you're dealing with code and you don't know what it is, get into the mindset of keeping people from being electrocuted, burned up, breathing poisonous fumes, or having stuff drop out of the ceiling on them.

That last one is why stuff should not be laid across ceiling tiles. Also, Romex on a ceiling tile, in a fire, will first create poisonous fumes (is there plenum Romex?). Then, when the insulation melts, it will electrically energize the entire T-bar grid until a circuit breaker blows.


I first saw this enforced in a TI build-out in 1988. The code, taken literally, said that each low-voltage wire must be separated from each other wire by some distance which I forget. The upshot was that the code made it legally impossible to run 3-pair phone wire out to ten new stations. The answer? Ask the inspector what to do. He said to tie them together, just as we normally do, and attach ties so they are supported from the T-bar support wires that hold up the T-bar frame. Wires are to be between six and 12 incches above the ceiling tiles; supports are to be 48" max apart from one another. I can't see how this might have loosened up in the intervening time, but it might have gotten more stringent.


It is also amazing just how far you will go to meeting code if you just do the things like this that would keep you from being irritated if you had to service it.

Take the time to introduce yourself to the inspectors in your area and always ask them IN ADVANCE when you have a question how *they* want to interpret the NEC code.

So few people do this they will remember & maybe even respect you for asking.

It's been my experience they have a MUCH better attitude when approached like this.

The reason everybody you'll ask has different experiences & opinions is it's all in how *their* local inspectors read the code from area-to-area & year-to-year.

The CORRECT answer is usually whatever your local guys say it is, and they can change their minds as they need and/or want to. They are not always just being inconsistent for sport, they learn about new *issues* all the time, just like we do. Some of their issues make the front pages, so that's their mindset sometimes.




Edit... Ernie types faster than I do..


Yeah... what he said.

The National Electric Code (NEC) is published by the National Fire Protection Association 800-344-3555. Call them and request a catalog. You can order hundreds of code books written by NFPA. The NEC is NFPA70. It has requirements for low voltage grounding, TV Antennas, Cable TV, telephone lines, fire alarm wiring, security wiring, computer, intercom, music systems, satellite dishes etc. as well as requirements for high voltage. I would recommend that you purchase the NEC Handbook instead of the NEC code book. The Handbook has all of the NEC code plus commentary about why the code requires certain things. Knowing why helps you understand the need to do it the right way. It has a good explanation why the cable TV ground, antenna ground, satellite dish ground, telephone ground, security system ground and electrical panel ground must be tied together. Some areas may require permits to do low voltage work and other areas do not. Check with the AHJ (Authority Having Jurisdiction). The AHJ may be the local building department. If your local jurisdiction has adopted a version of the NEC then IT IS THE LAW. Even if you are not required to pull a permit, YOU ARE REQUIRED TO FOLLOW ALL REQUIREMENTS OF THE NEC THAT PERTAIN TO THE LOW VOLTAGE WORK YOU DO. If lightning strikes a building and someone is injured or a fire starts or expensive equipment is damaged because your low voltage work was not properly run or grounded, the insurance company and the attorneys will be contacting you. Remember Olin’s Law, “There will be a fatal fire tomorrow, and the next day you will be in court explaining why you did what you did and why you didn’t do what you didn’t do”.

Whew! I’ll step off the soap box now.