Unlisted Cable entering a building

[John Adams]

LOTS of opinions on the 50 foot rule for unlisted cables (in my case telecomm cables)
I teach telecomm courses worldwide mainly for the US military and have done so for 20+ years. This is my opinion
The 50 foot limitation can be exceeding if the proper (NEC compliant) conduit system is placed as the raceway in the building. For metallic cables I must use RMC, IMC only. For non-metallic cable (fiber optics with no metallic components such as armor), I can use RMC, IMC, EMT, and PVC. If this practice is acceptable to the AHJ, I'm thinking I'm OK. The key to this is make sure we understand "point of entrance per the NEC.

Your thoughts?

 

[tom baker]

There are NEC rules on this in Chapter 8 (the unused pages).
Many of us are not familiar with these rules.
Can you summarize and post?

 

[John Adams]

Hey Tom
I go back to the very old days of telecomm cables all being copper and the outside sheaths being PVC or lead sheath. But today belongs to fiber and will continue to be the cable of choice for MANY years. Because of the hazardous potential of cable sheaths (rapid fire spread and not so nice fumes, the NEC only allows us to go no further than 50 feet (including slack that we always leave) into the building. That 50 ft rule is measured from the point of entrance which is usually as the cable breaks through the outer walls, ceilings or floors. But it allows the "point of entrance to be extended by doing what I said in my original quote.
hope that helps Tom

 

[don_resqcapt19]

This was addressed in a 2017 code change to 800.48.

800.48 Unlisted Cables Entering Buildings.
Unlisted outside plant communications cables shall be permitted to be installed in building spaces other than risers, ducts used for environmental air, plenums used for environmental air, and other spaces used for environmental air, where the length of the cable within the building, measured from its point of entrance, does not exceed 15 m (50 ft) and the cable enters the building from the outside and is terminated in an enclosure or on a listed primary protector. The point of entrance shall be permitted to be extended from the penetration of the external wall or floor slab by continuously enclosing the entrance cables in rigid metal conduit (RMC) or intermediate metal conduit (IMC) to the point of emergence.

The bold text was added, but it only permits the extension of the point of entrance where the unlisted cable is installed in RMC or IMC. The other wiring methods you mentioned are not permitted by the NEC to extend the point of entrance.
That rule is found in 805.48 in the 2020 code.

 

[John Adams]

This was addressed in a 2017 code change to 800.48.

The bold text was added, but it only permits the extension of the point of entrance where the unlisted cable is installed in RMC or IMC. The other wiring methods you mentioned are not permitted by the NEC to extend the point of entrance.
That rule is found in 805.48 in the 2020 code.

Don
You're looking in 800...................look at 770 Fiber Optic Cables. Thats where you'll find RMC, IMC, EMT, and PVC.

 

[don_resqcapt19]

Don
You're looking in 800...................look at 770 Fiber Optic Cables. Thats where you'll find RMC, IMC, EMT, and PVC.

There is nothing in 770.48(B) that actually changes the point of entrance by the use of a raceway. It simply permits the fiber to be installed in those raceways. The only permission to extend the point of entrance is found in 770.48(A) and as with the copper cables, it is limited to using RMC or IMC.

 

[hbiss]

The difference between copper OSP and fiber is that the copper will have a flooding compound (grease or gel) to keep water from entering and migrating. Fiber does not. The flooding compound in many instances is flammable which is why large count copper indoor terminals will have enclosed compartments on the OSP side.

It looks like this is why the NEC wants only RMC and IMC used with copper while with fiber you can use anything.

-Hal

 

[Electromatic]

Loose tube fiber optic cables are also usually gel-filled. I don't know that I've ever looked into the properties (flammable, etc.) of the gel, but I do know I'd rather work with tight-buffered fiber given the choice.

 

[tom baker]

The difference between copper OSP and fiber is that the copper will have a flooding compound (grease or gel) to keep water from entering and migrating. Fiber does not. The flooding compound in many instances is flammable which is why large count copper indoor terminals will have enclosed compartments on the OSP side.

-Hal

The flooding compound is called icky pick. gets on everything and hard to get off
I have seen outside non listed coax inside a building melt from a car pole accident. once inside the bldg, install a protector and ground

 

[John Adams]

There is nothing in 770.48(B) that actually changes the point of entrance by the use of a raceway. It simply permits the fiber to be installed in those raceways. The only permission to extend the point of entrance is found in 770.48(A) and as with the copper cables, it is limited to using RMC or IMC.

Don-

2020 770.48 (B) seems to indicate RMC, IMC, PVC, and EMT. What am I misreading or misunderstanding? Thanks for your help

 

[hbiss]

Not looking at the 2020. Don't go by it unless it applies to you. We are on the 2017 here.

-Hal