One Outlet in the Floor Is Usually Three Separate Orders
The most common mistake in this category is treating a floor box as a single item. In practice a working floor outlet is a box, a cover assembly with a flange matched to the floor finish, and the device inside it, and those are frequently three different part numbers. Knowing that before quoting saves a return trip. Lumera groups the whole enclosure range, floor boxes included, under the boxes and enclosures category.
What Is Under the Floor Decides the Box
Everything starts with the construction below the finished surface, because that is what physically constrains the choice.
- New concrete slab: a cast-in box is set and leveled before the pour, sealed against wet concrete, usually with height adjustment to land flush with the finished floor
- Existing concrete slab with occupied space below: a poke-through assembly drops into a cored hole and feeds from the ceiling cavity underneath
- Wood or raised access floor: a shallow box drops between joists or into the plenum, often nonmetallic or stamped steel
The distinction that catches people is the second one. On a retrofit into a finished slab with no chase below, a poke-through is frequently the only legal option, and it is a different product with different code implications from a new-construction box.
Poke-Through and the Fire Rating It Has to Restore
This is the part that generates inspection problems. Coring a hole through a concrete floor between two occupied levels breaks whatever fire resistance rating that floor assembly carried, and the assembly that fills the hole has to put the rating back.
A listed poke-through does that with an intumescent material that expands under heat and seals the opening. That is why it costs more than a plain box, and why an ordinary box dropped into a cored hole is not an acceptable shortcut. The rating belongs to the tested assembly, so use a listed unit and keep the documentation with the job file for the inspector.
Covers and Flanges Are Chosen by the Floor Finish
The cover is where most of the visible cost and most of the ordering confusion sits, and it is selected against the finished floor rather than against the box.
A carpet flange grips the cut carpet edge so it does not fray around the opening. A tile flange sits recessed so stone or tile can be set into it and finish flush. A wood flange trims out against hardwood. Get this wrong and the installation looks unfinished no matter how well the box was set.
The cover itself is a separate decision again. A flush plate closes the opening completely when nothing is plugged in, a hinged flip lid opens for daily access, and a while-in-use style closes over a permanently connected cord. Finishes across the range include brass, nickel-plated brass, and aluminum, normally chosen to match the room rather than the box body.
Lumera groups covers and rings for the wider box range in the electrical box covers and rings collection, and the cover belongs on the same order as the box itself.
Screw Lid or Hinged Lid
Lid style follows how often the outlet is actually used. A screw lid seals tightly and suits a location that is connected once and then left, such as a fixed display or built-in equipment. A hinged or flip lid opens with a finger and stays captive, which suits a conference table or a retail floor where cords come and go daily.
Several assemblies in this range are offered in both styles under adjacent part numbers, differing only in the lid, so read the full product title rather than the base number.
Single-Service or Multi-Service
A single-service box carries power only, which covers most restaurant and retail locations. A multi-service box splits internally into isolated compartments so line-voltage power and low-voltage data can share one opening without sharing a cavity.
That separation is not cosmetic. Keeping power and data physically apart limits interference on the data side and is generally required by the low-voltage standards a structured cabling contractor works to. In an open-plan office or a conference room, multi-service is the right specification, and the cover presents receptacles beside keystone or connector openings.
The receptacles that mount inside the box are ordered separately, and Lumera's receptacles collection covers those devices.
Depth, Volume, and What Will Actually Fit
Floor boxes are constrained in a way wall boxes are not, because the available depth is set by the slab or the joist bay rather than by choice. A shallow box in a raised floor may not have the internal volume the design assumed, and the standard box fill calculation still applies down there.
Work out the fill before selecting, particularly on a multi-service box where the compartment divider consumes usable space. Where the box turns out to be the wrong size, the answer is a different box rather than a forced install, and Lumera's device and outlet boxes collection covers the wider range of sizes.
Foot Traffic, Spills, and Listing
A floor box is walked on, rolled over by chairs and carts, and mopped. Boxes and covers for this use are listed specifically for floor installation, rated to carry foot traffic, and built so cleaning water does not reach the devices inside, which is why a standard box with a flat plate is not a substitute. Match the assembly to the duty the location sees, because a conference room and a restaurant service aisle are not the same case, and the heavier cast assemblies exist for the second one.
Feeding the Box and Installation
The raceway feeding a floor box is usually run before the pour or fished through the ceiling below, and the fittings entering the box have to suit both the raceway type and the box. Lumera's conduit and fittings category covers that hardware.
Installation is licensed electrician work, and on a cast-in box it also has to be coordinated with the pour, which fixes the box position and height long before the finish floor exists. Confirm the finished floor thickness with the general contractor before setting height, because a box that ends up proud of the tile or buried under it is an expensive correction.
Floor Box FAQs
What is the difference between a poke-through and a cast-in floor box?
A cast-in box is set before a new concrete slab is poured and sealed against the wet concrete. A poke-through drops into a cored hole in an existing floor and feeds from the space below. Use cast-in for new construction and poke-through for retrofits into a finished slab.
Does a poke-through affect the floor's fire rating?
Coring the hole breaks it, and the assembly has to restore it. A listed poke-through contains intumescent material that expands under heat to seal the opening, which is why an ordinary floor box cannot be substituted into a cored hole. Keep the listing documentation with the job file for inspection.
How do I choose the right cover and flange?
Choose against the finished floor, not the box. A carpet flange grips the cut carpet edge, a tile flange recesses so stone or tile finishes flush, and a wood flange trims against hardwood. Then pick the cover style separately: flush plate, hinged flip lid, or a while-in-use type for a permanently connected cord.
Can one floor box carry both power and data?
Yes, using a multi-service box that divides internally into isolated compartments. The separation limits interference on the data side and is generally required by low-voltage cabling standards. A single-service box carries power only and suits most retail and restaurant locations.
Can I use a regular electrical box in the floor?
No. Floor boxes and their covers are listed specifically for floor use, rated to be walked on, and built so mopping water does not reach the devices inside. A standard box with a flat plate meets none of those requirements even where it physically fits.
Do I need to order the cover separately from the box?
Usually yes, and it is the most common ordering gap in this category. A working floor outlet is typically three purchases: the box, the cover assembly with the flange matched to the floor finish, and the device inside. Check what each listing actually includes before ordering.
