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How to Install a Floor Outlet

Say goodbye to hazardous extension cords

how to install a recessed floor outlet boxFamily Handyman

Sometimes electricity is just not where you need it, especially in big rooms and in older houses. A floor outlet may be the perfect way to solve the problem.

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Time
A full day
Complexity
Intermediate
Cost
$51–100

Put an outlet where you need it

Until someone comes up with a better idea, we’re stuck with plugging lamps into outlets to get light. But what if you want a lamp in the middle of the room where there’s no outlet? You don’t have to resort to ugly and dangerous extension cords. We’ll show you how easy it is to put the power where you need it by installing a handsome, stampede-proof, moisture-proof outlet in your floor (assuming your floor’s not concrete!).

Cutting in and mounting the steel outlet box is a job anyone with basic carpentry skills can handle. Connecting the power is a little trickier because it requires you to locate a suitable circuit and make electrical connections. If you’re uncertain how to do it, consult a basic house wiring book or a local electrician for help.

Before starting any electrical work, contact your electrical inspections department for a permit. A permit fee is a small price to pay for the assurance that the wiring is safe, and you might even get some free advice from the inspector. (See Top 10 Electrical Mistakes to see some common mistakes to avoid.)

Besides basic tools like a hammer, tape measure and screwdrivers, you’ll need a drill and a 3/32-in. bit, 3/8-in. and 5/8-in. spade bits and a jigsaw. You’ll also need a needle-nose pliers, a pocketknife or utility knife, a wire stripper and a voltage tester.

CAUTION!

If you’re pulling power from an existing junction box or receptacle, check the color of the bare wire ends. If they’re gray rather than dull brown, they’re made of aluminum rather than copper. Call in a licensed electrician to connect the old aluminum wires to the new copper wires.

Buy a special floor assembly – a regular wall outlet won’t do

Photo 1: Find a location for a recessed floor outlet box

Measure from a reference point, such as the radiator heating pipes shown, to locate the floor outlet so it falls between the 2×10 floor joists. Then use an 8-in. straight length of clothes hanger, snipped off at an angle to form a point, as a locator bit. Start the drill slowly while holding the hanger to keep it from whipping around as you drill through the flooring.

Photo 2: Find the clothes hanger bit

Find the protruding clothes hanger in the open ceiling below. If there are no obstructions and this is a suitable spot for a floor outlet, proceed with the installation.

The National Electrical Code requires floor outlets to be a part of an approved assembly consisting of a metal box, gasket seal, special receptacle and strong cover plate with a moisture-proof cover. You can’t just mount a regular wall outlet in the floor. The first time someone stepped on it, it would break. Besides, mopping a floor around an outlet that doesn’t have a moisture-proof cover could cause corroded connections, or worse, give you a lethal shock.

The residential floor box assembly we’re using may be available at home centers, but if you can’t find one there, you’ll find a selection at a local electrical supply store that caters to professionals. You can find a Tamper Resistant Receptacle Floor Box Kit online, available through our affiliation with Amazon.com.

In addition to the floor box assembly, buy enough cable to connect the outlet to the power source. With a few local exceptions, you can use plastic-sheathed cable (technically called Type NM-B). Use 14-gauge wire if the circuit you’re connecting to is protected with a 15-amp fuse or circuit breaker (12-gauge wire for 20-amp circuits).

You’ll also need at least one plastic cable clamp (Photo 6), wire connectors (Photo 10), 1/2-in. plastic staples (Photo 10) and 1/2-in. x No. 4 flathead screws.

Pick a location you can reach with the power cable for a recessed floor outlet box

Photo 3: Cut a hole for the recessed floor outlet box

Outline the outlet box on the floor. Drill two 3/8-in. holes at the corners where the screws protrude from the sides of the metal box and two more where the outlet mounting screws go. Now use a jigsaw with a wood-cutting blade to complete the box cutout. Apply masking tape to protect the floor finish.

Photo 4: Make the recessed floor outlet box flush

Chisel shallow notches to accept the mounting ears. Then place the box in the hole and drill 3/32-in. pilot holes for the four mounting screws. Determine where the wire will enter the box and remove the appropriate round metal knockout plug with a needle-nose pliers. Screw a No. 10-32 green grounding screw into the threaded hole in the bottom of the box. Then attach the box to the floor with the 1/2 in. No. 4 flathead screws.

You can put a floor outlet anywhere, but getting the cable there can be tough. So keep routing problems in mind when you choose a location. Floors over unfinished basements or crawlspaces are easy to reach from below. Concrete floors are tougher because you have to cut a trench to the nearest power source. Floors with a finished ceiling below present a challenge that can usually be overcome with some ingenuity. See Fishing Electrical Wire for details on how to pull cable through finished walls and ceilings.

Locate the floor joists before you cut the outlet hole. Use heat vents, cable or plumbing pipes that penetrate the floor and are visible from below as reference points. Drill a small hole through the floor (Photo 1) where you intend to place the outlet and locate the bit from the open ceiling below. If you drilled directly over a joist, you won’t be able to see the bit. Move over a few inches and try again. Patch the misplaced hole in the floor with matching wood putty. We used a cut-off clothes hanger as a drill bit because it’s cheap, handy and easy to spot from below. This homemade clothes hanger bit is a must for carpeted floors because the smooth sides won’t catch the carpet fibers like a regular drill bit.

Find a circuit to supply power

Photo 5: Run the cable

Run plastic-sheathed cable from the floor outlet to the power source. See the guidelines in the next step for drilling and stapling the cable.

Photo 6: Lock the wires into the box

Attach the cable to the new box. First slit the plastic sheathing with a utility knife or special slitting tool to expose 12 in. of the enclosed wires. Then secure a plastic cable clamp to the cable, allowing 1/4 in. of the plastic sheathing to extend beyond the clamp. Push the wires into the box and snap the cable clamp into the knockout hole. Now secure the cable within 12 in. of the metal box with a plastic cable staple.

Most open ceilings have light-fixture boxes and metal or plastic junction boxes where a number of cables are joined. Both offer potential sources of power for your floor outlet, but a ceiling light box like the one shown (Photo 9) that’s switched with a pull chain rather than a wall switch is most likely to contain “hot” wires suitable for connecting the floor outlet.

Turn off the circuit breaker or unscrew the fuse that controls the circuit you’ve chosen. If your light fixture box is like ours, just turn on the light and have a helper watch it as you switch off the circuit breakers one at a time until the light goes out. Leave this circuit breaker switched off.

If the electrical junction box you’ve picked doesn’t have a light fixture, you’ll have to use a voltage tester to determine which circuit breaker or fuse to turn off. This process can be complex. If you don’t have electrical experience or are unsure how to do this, don’t hesitate to enlist the help of a licensed electrician.

A word of warning is in order here. Some electrical boxes contain more than one circuit. Before doing any work in the box, test all the wires in a box with a simple neon voltage tester (Photo 9) to make sure they’re “dead.”

The electrical code requires two additional steps to ensure safety:

  1. Determine if the circuit you want to use can handle the additional outlet without overloading. Do this by shutting off the circuit at the main panel. Then go through the house turning on lights and other electrical items. Add up the wattage for everything that doesn’t go on, including things that are normally plugged in, such as stereos and televisions. Then add the wattage of the lamp you’ll be plugging into the floor outlet. The National Electrical Code (NEC) allows a total of 1,800 watts for a 15-amp circuit; 2,400 for a 20-amp circuit. The amp rating of the circuit is printed on the circuit breaker or fuse. If the total wattage exceeds these amounts, you’ll have to find a new circuit. Also, as a rule of thumb, don’t use a circuit if it has any device drawing more than 7.5 amps either plugged in or directly wired to it.
  2. To figure out if there’s enough space in the box for the minimum box size required by the NEC, add: 1 for each hot and neutral wire entering the box, 1 for all the ground wires combined, 1 for all the clamps combined, and 2 for each device (switch or receptacle) installed in the box. Multiply this figure by 2 for 14-gauge wire and 2.25 for 12-gauge wire to get the minimum box volume in cubic inches. Plastic boxes have their volume stamped inside. Steel box capacities are listed in the electrical code. Call the electrical inspector for that information. If the box you want to use isn’t big enough, add a box extension or replace the box with a larger one. For more information on sizing an electrical circuit, see Preventing Electrical Overloads.

CAUTION!

The electrical code prohibits any connections to “dedicated” circuits, such as 20-amp small-appliance circuits in kitchens and dining areas, 20-amp laundry circuits and 20-amp bathroom circuits. If you’re unsure about your circuit, ask the electrical inspector.

A first-rate electrical job mostly means getting the details right

Photo 7: Wire the receptacle

Snip off the wires so they’re at least 6 in. long and protrude from the top of the metal box at least 3 in. Strip 5/8 in. of insulation from the black and white wires with a wire stripper. Connect the bare ground wire to the metal box by looping it once in a clockwise direction around the green grounding screw and tightening the screw. Loop the end of the same bare grounding wire clockwise around the grounding screw on the receptacle and tighten the screw. Connect the black wire to the brass screw and the white wire to the silver screw.

Photo 8: Add the cover

Mount the receptacle to the outlet box. Fold the wires neatly and push the outlet into the box. Screw the outlet to the metal box with the machine screws. Then position the foam gasket over the receptacle and attach the brass cover plate with the small cover plate screws. Screw the brass plug with the rubber O-ring seal into the hole to protect the outlet from dirt and moisture when it’s not in use.

Photo 9: Test for live wires

Switch off the circuit breaker or remove the fuse at the main panel to disconnect the power to the wires in the junction box you’re hooking up to. Double-check that the power is off by holding one lead of a voltage tester against one light-fixture terminal screw and the other against the bare copper grounding wire. Check the other terminal the same way. If the tester lights up, the power is still on. Do not continue until you find and turn off the correct circuit breaker.

Photo 10: Connect the new wires

Punch out one of the knockouts in the plastic or steel junction box. Push the wires into the box until 1/4 in. of the sheathing is visible inside of the box, then clamp them in place. Remove the wire connectors one at a time. Line up the end of each new wire in turn with the ends of the existing wires and reconnect them with a new wire connector. Connect the bare ground wire to the ground wires, the neutral white wire to the neutral white wires, and the black wire to the red or black hot wire or wires.

Photos 2, 3 and 4 show how to cut in and install the steel outlet box that’s included with the floor outlet assembly. Mount the box. Then run the cable from your power source to the floor outlet.

Follow these rules if you have to drill through joists.

    • Avoid drilling holes in the center one-third of the span or length of the floor joist.
    • Holes must be a minimum of 2 in. from the top and bottom edge of the joist. Staple the cable with special 1/2-in. plastic NM cable staples every 4-1/2 ft. where it runs along the joist. (TIP: For a neater, easier job, unroll the cable and remove the twists before installing it.) Don’t staple either end of the cable yet, and leave at least 1 ft. of extra cable on each end.

Photos 6 – 8 show how to wire the new outlet. For more information, see How to Make Safe Wire Connections.

When the floor outlet connections are complete, move to the basement and connect the other end of the wires to the power in the ceiling box (Photos 9 and 10). You’ll have to remove a “knockout” plug with a screwdriver or needle-nose pliers to provide a hole for the cable to enter the box. Attach the cable to the box with a cable clamp. Many boxes have built-in clamps. Connect the wires as shown in Photo 10. Match the wire connectors you’re using to the number of wires being connected. Red connectors like the ones we’re using can usually connect up to five 14-gauge or four 12-gauge wires, but check the manufacturer’s specifications on the package to be sure. Replace the light fixture or cover plate to complete the wiring job.

For outlet installations on carpeted floors, the top edge of the outlet box must be flush with the carpet. Flipping the outlet ears over before mounting the box is one easy way to accomplish this.

Your new floor outlet is strong enough to withstand occasional abuse, and with the cover and gaskets in place you’ll be able to damp-mop the floor without worrying about getting shocked or damaging the wiring. Keep a record of the manufacturer’s name in case you lose the cover and have to order a new one.

Required Tools for this Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • 4-in-1 screwdriver
  • Cordless drill
  • Drill bit set
  • Jigsaw
  • Needle-nose pliers
  • Non-contact voltage tester
  • Utility knife
  • Voltage tester
  • Wire stripper/cutter
  • Wood chisel

Required Materials for this Project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Electrical cable
  • Floor box assembly
  • Metal coat hanger
  • No. 4 x 1/2-in. flathead screws
  • Plastic cable clamps
  • Plastic staples
  • Wire connectors