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#219010 01/10/18 01:55 PM
Joined: Jan 2018
Posts: 22
L
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The National Electrical Code definition of Point of Entry for fiber optic cable (NEC 2014, Article 770.2) states:

"The point within a building at which optical fiber cable emerges from an external wall, from a concrete floor slab, from rigid metal conduit (RMC), or from intermediate metal conduit (IMC)."

My question is if a conduit run that contains metal pull boxes is used to create a distant Point of Entry within a building, is this still code compliant, or are pull boxes not allowed?

I would think that it would still be compliant, otherwise a long conduit run without pull boxes could be impractical, but I don’t know if a pull box would be considered as exposing the cable. Code prohibits non fire rated cable from running more than 50’ exposed from the Point of Entry.

2017 / 2014 NEC & Related Books and Study Guides
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G
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As a general rule you don't use the "definition" section to describe methods. That is just defining terms. Go down to section II in article 770 to read more about fiber entering buildings. (starting at 770.47)
If you look at raceways in Chapter 3 of the code you will see that boxes and conduit bodies are considered to be part of the raceway system if they are installed in the correct manner so that part of your question is "yes" they are allowed in that system.


Greg Fretwell
Joined: Jan 2018
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Much appreciated - that answer was right on target.

Article 770.48 was the motivation for my asking the question, but I didn't think of the Chapter 3 information regarding raceway components that you pointed out. Thanks.

Joined: Jan 2018
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Recently had occasion to address this situation again, and I now believe that the conclusion from the original discussion was incorrect. While the requirements of Article 770.48(A) haven’t changed, in the 2017 NEC a paragraph was added to 770.48(A) to clarify those requirements. In particular, it states that to extend the point of entrance, the cable must be "continuously" enclosed in IMC or RMC. That would seem rule out such things as pull boxes which would ordinarily be allowed in a raceway system. Had I looked at the 2017 NEC (instead of 2014) when I originally asked the question, well..……..I wouldn’t have needed to ask.

I know that no one has been losing sleep over this scenario, but I just wanted to set the record straight (at least as I now believe it to be).

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G
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I still think conduit bodies are part of the raceway system, otherwise they would be limited to 4 bends (360 degrees).


Greg Fretwell
Joined: Jan 2018
Posts: 22
L
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I suspect that new paragraph with the "continuously enclosing" wording was inserted in the 2017 NEC explicitly to clarify that conduit raceway system components are not permitted - otherwise why add the paragraph? I don't think the NEC cares about cable pulling difficulty in this situation, and it's one reason why splicing an indoor fire rated fiber cable to the non-rated outside plant fiber cable was a common solution (plus the expense of installing IMC/RMC vs EMT or just indoor innerduct). Today there are fiber cables rated for dual outside/inside plant use that avoid the issues around extending a point of entry for non-rated cable. However, for many applications in the outside plant a non-fire rated PE jacketed cable is still preferred, and so the 770.48(A) conduit requirement comes into play when the termination location is more than 50' from the building entry point and it is desired to bring the outside plant cable to that location - which is the case I looked at.

Note that although the NEC allows for up to 4 x 90 degree bends (360 degrees), in the telecom world only 2 x 90 degree bends (or a total of 180 degrees) are permitted between pull points if one follows the major telecom standards requirements (often required on design prints). These standards also have an allowable bend radius for a given size conduit that is larger than what the NEC accepts due to bend radius limitations on communications cables that aren't applicable to general electrical wiring.


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