Floor boxes and associated raceway

[ZSIM]

Greetings. I am looking to learn something about floor boxes that perhaps I've been negligent of in my career so far.

I've always been under the impression that floor boxes, when installed in slab-on-grade concrete flooring, utilized "in-slab" raceway. It is not something I've come across often, but the products I've seen from Legrand, Arlington, etc. usually depict and suggest the raceway running in the slab.

I have an individual however who is telling me that we should never run the conduit in-slab; the raceway should always be run under the slab (for both new work and old work). In their judgement for an existing facility you would cut the slab from box location to wall, but then trench down slightly to install the raceway in the base/subbase under the pad.

I cannot find a product that necessarily supports this method of installation, and it seems to add significant labor plus the possibility of moisture ingress into the raceway system by being in the mediums under the slab... but I am very inexperienced here and looking for what the better approach generally is considered.

What is your preference (in-slab or under slab) and which do find to be the superior installation method? Thank you.

 

[infinity]

I see zero reason not to run in the slab. If the building owner is worried about chopping or cutting the slab in the future then they should pay extra to not have the raceway within the concrete.

 

[Sberry]

Dealers choice. If its something I ever wanna work on/add to want it under, lets it thermal on its own under a little sand. Anything encased is hard to work on.

 

[hillbilly1]

Nothing wrong with putting it in the slab, if it’s too shallow, cracks may form afterwards though. There always is an issue of cutting into it later, but the slab can be x-ray’d to locate. Some stores no longer allow it in the slab because of the danger of cutting it or driving an anchor through it. Floor duct (D-duct, or Walker duct, just to name a few) was popular for cash register lines many years ago, but due to frequent remodeling not lining up, rodent damage to wiring, power poles from the ceiling is now the norm.

 

[ZSIM]

Thank you all for the feedback. It’s helpful to know I’m not completely in the dark sometimes!

 

[Fred B]

plus the possibility of moisture ingress into the raceway system by being in the mediums under the slab...

Seen that exact thing. Pipe full and floor box with several inches of water in it. When tried to pull wire found conduit had separated and shifted in the gravel medium. Another crew was tasked to cut in a new conduit and ended up cutting through another live circuit pipe. Needless to say sparks flew.