Mike Dolt Enterprises
Mike Dolt Enterprises
User: aaronbailey52, Location: Massachusetts
Asked on: Thursday, April 14, 2011 at 5:34 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:12 am EDT
Question: 250.52 (2011)Note: Concrete containing insulation, vapor barriers, films or similar items separating it from the earth isn?t considered to be in ?direct contact? with the earth.100 (2008)Location, Wet. Installations underground or in concrete slabs or masonry in direct contact with the earth;For 250.52, the conclusion I've drawn from much too much googling is that there is a consensus as to it being critical for the bottom of a slab or footing to be in direct contact with the earth, i.e. no vapor barrier beneath, even though the concrete is in direct contact with the earth from the sides. Is it reasonable or is it bonkers to then consider conduit in slab on grade above a vapor barrier to be in a wet location, even though per 250.52 it is not in direct contact with the earth, even though it is???I have a contractor who installed plenum data cables in slab on grade and several "buildings" per NEC definition of building all tied to one grounding electrode (triad tied to centrally located ground bus bar in one of them). All electrical rooms are bonded to building steel, or will be (why would they power everything up before finishing all grounding and bonding connections??? Is that stupid or are my thoughts clouded by the moisture behind my ears???). So, if my footings, etc, are not in direct earth contact, my structural steel is not a grounding electrode. But, if I'm not in direct earth contact with my slab/footings, then how do I get my plenum rated cables replaced when I'm sure they will fill up with water, eventually.
Regarding the Wet Location Classification
250.52
Concrete in direct contact with the earth is considered a wet location because it can absorb moisture from the ground. However, if the concrete is separated from the earth by an insulating material, vapor barrier, or similar items, it is not considered a wet location.
100
Conduit in slab on grade that is not in direct contact with the earth is not considered a wet location. This is because the vapor barrier beneath the slab prevents moisture from the earth from reaching the conduit.
Conclusion
Based on these definitions, it is reasonable to conclude that conduit in slab on grade above a vapor barrier is not in a wet location, even though the concrete surrounding the conduit is.
Grounding Considerations
If the footings are not in direct contact with the earth, the structural steel cannot be used as a grounding electrode. In this case, you can use a separate grounding electrode, such as a ground rod or concrete-encased electrode. The electrical rooms should be bonded to the grounding electrode to ensure proper grounding of the electrical system.
Plenum Cables
If you are concerned about moisture entering the plenum cables, you can consider using a different type of cable that is rated for wet locations. Alternatively, you can install the plenum cables in a conduit or raceway that is sealed to prevent moisture ingress.
Additional Thoughts: It is always advisable to follow the manufacturer's instructions for the installation of cables and electrical equipment.* It is also important to have a licensed electrician inspect and test the electrical system to ensure it meets all applicable codes and standards. Flag for review