150 ft requirement for IDF room?

[David Christian]

Hi guys,

I have a question need your help and suggestion. I really appreciate any suggestions and ideas.

I recently just start to design a project with about 80 units and 3 retail stores and 1 leasing office.

This week I attended the meeting with the architect, contractor and owner. The electrical contractor noted that distance from residential unit to IDF room must be less than 150 ft.

Is this code requirement or TV coax cable maximum distance requirement? If so, I think I need to provide at least 3 IDF rooms to meet this requirement.

I also want to know whether I need to provide separate IDF room only for leasing office.

Thank you very much!

 

[GoldDigger]

Other then attenuation at very high frequencies, there is no technical limit on the length of TV cable. Interactive (two way) systems may also have time latency issues for some protocols.
Digital network signal (such at ethernet over CAT5) may have cable length limitations though.
The longer runs to the IDF will be using different media or protocols, possibly fiber.

 

[zbang]

Lessee-
Cable TV- no practical limit within buildings
POTS and DSL lines - no practical limit within buildings
Twisted-pair Ethernet - 100m (330')

I know of no 150' requirement, residential or commercial, in any code. EC mentioned it, what's their citation for it? Certainly many condo or apartment blocks have one LV closet for an entire building. OTOH, with that many cable drops, they won't all be home-run to a main closet, so the system will probably have at least one amp and a pile of splitters spread around the building; they have to go somewhere.

Also, an IDF could be a 2' cube in a mechanical room, not necessarily a dedicated room, or even closet.

 

[hbiss]

Sounds like the cable company maintaining their requirements for drops from pole or pedestal to house. They normally use a RG6 size cable up to 150' but more than that they go to something larger like RG11 or even hardline.

In this instance the IDFs will have taps like on the pole with a run to each apartment, hence the 150' max requirement. There, it will split to the individual wall plate runs. So I'm sure they specified an RG6 size cable for the EC to install.

It will be up to the cable company to provide and install the hardline, taps and required amps within the building to supply however many IDFs are needed. I guess you just have to make room for them.

-Hal

 

[JFletcher]

No requirement I know of either, even by TDMM standards. Many hotels exceed 150' from wallplate to IDF (if there is one) because the IDF will be at the far end of a floor. Practically, Ive run CATV RG6 up to 360' in a building and not had any problems. Do not use any splices on long runs. Not because they really degrade the connection, but they will be impossible to find/access once the building is complete.

It certainly doesnt hurt to have more IDFs and get the cable co to run their trunk lines and taps closer to point of use. as zbang wrote, twisted pair ethernet (data) does have a hard limit of 100M before you need switches or what not, and that is usually the limiting factor.

150' is a pipe dream tho. Tons of hotels have no IDFs or they are at the end of the hall, and the cable drops from tap to wallplate routinely exceed 200'. as Hal would no doubt mention, run all home runs and let the cable co do the terminations both sides; some will require that, and some have their own guys do the cable start to finish - they sometimes dont want to inherit problems from someone else's install. Also, some cable co's will give you the cable they want installed, so it never hurts to ask.

 

[hbiss]

No requirement I know of either...

I have no doubt that the cable company was consulted about the design and this is where the requirement came from, for the reason I mentioned above.

I also have no doubt that other contractors, left to their own devices on other jobs did what they felt like then had the cable company come in after it was finished to try and make it work. The fact that they were able to get satisfactory results doesn't mean that the EC did the right thing.

There are plenty of older hotels and motels wired with RG59 or long runs of RG6 that are cost prohibitive or impossible to rewire, so dealing with high loss cable in today's Ghz systems can sometimes be done. But that sort of thing shouldn't be an issue with new builds just because the EC or GC doesn't want to bother dealing with the cable company design department.

-Hal