518-4 Places of Assembly

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dshipcott

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518-4 says that non metalic raceways shall be encased in 2" of concrete. Other than under a concrete slab, can you give an example of an installation that would include a 2" concrete envelope around the conduit?
Is the code refering to non metalic conduit runs outside of the building that feed or support places of assembly?
 
Re: 518-4 Places of Assembly

You could and we sometimes do for service conductors have the carpenters build a form around the raceway and literally encase the raceway in concrete up through walls etc.

For service conductors it may be unavoidable but for feeders and branch circuits in a place of assembly I would just use metal raceways. ;)
 
Re: 518-4 Places of Assembly

Using a metal raceway makes sense.
My question is what is the intent of the code?
Why is that requirement included?
 
Re: 518-4 Places of Assembly

Any non-metallic raceways in side the place of assembly.

In case of fire they do not want the non-metallic raceways to add to the smoke load in the building.
 
Re: 518-4 Places of Assembly

518-4(C)(1) allows non metalic conduit if concealed in a rated wall floor or ceiling. No mention of concrete.
I am trying to imagine an application where the non metalic conduit would be encased in concrete other than underground.
 
Re: 518-4 Places of Assembly

518-4(C)(1) allows the use of non-metallic raceways behind rated finishes in only the listed locations, not all places of assembly.

You have to read all of 518-4(C)(1) for the particular places of assembly it covers.
 
Re: 518-4 Places of Assembly

Thanks for your replys.
So in the exception you can install PVC in a conferance and meeting room but not a Multipurpose room because a multipurpose room is an area listed as a place of assembly not included in the exception.
What does not make sense about that interpretation is that many of the rooms not listed in the exception are interchangeable with the rooms listed in the exception.
 
Re: 518-4 Places of Assembly

Here is the origin of my interest in this subject. A structural engineer stated that a 3/4" PVC conduit installed in a structural concrete deck had to be spaced 2? from the face of the finished concrete. He sighted NEC 518-4 as the reason for the requirement. The structural deck is in between a parking level below and meeting rooms above.
 
Re: 518-4 Places of Assembly

I had heard that a contractor tried to claim that he totally encased the conductors with 2" of concrete because he stacked bags of premix concrete from floor to ceiling. The bags were not mixed, just stacked on top of each other. Has anyone ever heard of someone trying this or worse yet seen it in person?
 
Re: 518-4 Places of Assembly

Here is an example of concrete encasement. Before PVC was approved in the code for general use, it could not be run exposed, underground was OK. There is a outdoor service in an industrial park, with PVC conduit, that has a concrete encasement around the conduit, essentially concrete fence post with a conduit in it. I should take a picture of it sometime. It seems to me the NEC changed in 1981 to allow PVC exposed, after a lawsuit between the PVC and steel conduit industry that went all the way to the Supreme Court.

[ January 30, 2004, 01:04 AM: Message edited by: tom baker ]
 
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