This project is continued from Part 5.

Having fished a new run NM-B 12/2 cable from the circuit breaker panel through the crawlspace to the kitchen sink cabinet, I’m ready to wire the junction box and electrical receptacle. The materials used are illustrated in this photo:

Under Sink Electrical Outlet Wiring Parts List

Under Sink Electrical Outlet Material List

Referring to the letters in the above photo, the electrical parts are:

• A) Leviton T5020-W 20-Amp White Tamper-Resistant Single Outlet.
• B) Single gang metal outlet box
• C) Single gang metal outlet box cover with a single 20 AMP receptacle hole (1.594 inch diameter).
  Note: The photo shows a finish wall plate cover for fitting a recessed box in the drywall – which will work fine, however I actually used a simple box cover in the project.
• D) Double Snap Lock® Connector by Sigma Electric. Available at Lowes under as the Gampak 3/8″ BX-MC-Flex Connector, Item #: 111896, Model #: 45505 for about $2 for a bag of two connectors.
• E) 3/8 inch aluminum flexible conduit.
• F and L) NM-B 12/2 electrical cable
  I bought a 50 foot roll for about $32.50. The cost varies with the price of copper and has been going up in recent years.
• G) 4 inch metal box cover.
• H) 4×4 inch square by 1.5 inch deep metal box.
• I) #10-32 green ground screw, sold in bags of 10 screws.
• J) Red twist on Wire Nuts for minimum of two (2) #14 and maximum of four (4) #12 gauge wires.
• K) 3/8 in. Twin Screw Non-Metallic Cable Clamp Connector.
• (See below) 3/8 inch by 25 foot roll of aluminum flexible conduit

Under Sink Electrical Outlet Wiring Options

There are two ways to wire the branch circuit for the under kitchen sink electrical outlet:

A) With a 4 inch square junction box in the sink cabinet, or
B) Without a junction box.

These wiring options are illustrated in the following wiring diagrams.

Option A: 4 inch square junction box:

Under Kitchen Sink Electrical Outlet Wiring Diagram – Junction Box

Option B: No junction box – straight run of flex cable conduit from the kitchen cabinet bottom to the receptacle box:

Under Kitchen Sink Electrical Outlet Wiring Diagram – Straight Run

Comparing the two wiring options:

• Both methods are allowed by the National Electrical Code.
• Option A is a bit more work and requires a few dollars more in materials.
• Option B is simpler, less effort and materials. An electrician will most always use this technique.

I chose Option A. Why?

• I preferred the aluminum flex cable termination in the 4×4 inch junction box via the Double Snap Lock® Connector, instead of just poking the flex cable down a hole in the bottom of the kitchen cabinet.
• Junction boxes provide flexibility for future wiring additions.

Flexible Metal Conduit

NM electrical cable may not be exposed and must be protected per the National Electrical Code. 3/8 inch diameter flexible metal conduit (“flex conduit”) is perfect for this job. The conduit is hollow and the NM-B 12/2 cable is pushed into the conduit. A 25 foot roll cost about $11.00 at the home improvement store.

3/8 inch by 25 foot Roll of Aluminum Flex Conduit

There are two ways of cutting flex conduit:

• Untwist a section and cut it with metal snips.
• Use a hacksaw or power tool

I found it convenient to saw a ~2 foot section for the sink outlet with my Dremel tool and cutoff wheel. Makes for a clean even cut.

Cutting 3/8 inch Flexible Metal Conduit with a Dremel Tool Cutoff Wheel

Wiring the Under Kitchen Sink Junction Box

The yellow NM-B 12/2 cable is not connected to the electrical panel (never work on a live cable!) and hanging loose in the basement.I pulled up some cable to wire the junction box and electrical receptacle in a more comfortable location in the kitchen sink cabinet.

The junction box is wired by:

• Strip 6 inches of the yellow outer insulation jacket from the NM-B 12/2 cable, being careful not to cut the insulation on the black and white wires.
• Remove a 1/2 inch knockout and screw on the 3/8″ NM cable clamp in the side of the 4×4 metal junction box.
• Insert NM-B 12/2 cable through the clamp into the junction box. At least 1/4 inch of the outer yellow insulation jacket must be inside the junction box.
• Strip 5/8 inch of insulation from the black (hot) and white (neutral) wires.
  The red handle wire strippers to the right of the junction box in the photo below do a great job of stripping the insulation without cutting the copper conductors.
• Attach a 7 or 8 inch length of bare copper wire to the green ground screw. The ground wire is looped clockwise around the ground screw and the screw tightened. Trim the ground wire so it’s extends an equal length out of the junction box as NM-B cable wires.

I’ve also measured, cut and prepped the ends of a new section of NM-B 12/2 cable that is 1 foot longer than the metal flex conduit as shown in the foreground:

Wiring the Under Sink Junction Box: NM Cable Clamp & Ground Wire

The NM-B 12/2 cable is pushed through the 3/8 inch metal flex conduit as shown. I left the yellow outer insulation on the 12/2 cable which made for a snug fit. The Sigma Electric Double Snap Lock® connector is pressed onto the end of the flex conduit and snaps in place with metal tangs that won’t pull out. It’s a foolproof and professional system. The Sigma Double Snap Lock connector has a built-in red plastic anti-short bushing to protect the wires from the sharp ends of the flex conduit.

Metal Flex Cable with Sigma Electric Double Snap Lock® Connector

The Sigma Double Snap Lock connector is snapped into a 1/2 inch knockout hole on the opposite of the 4×4 junction box. The insulation is stripped 5/8 inch from the ends of the black and white wires as shown. Take care that all wires are equal length of at least 6 inches.

Under Kitchen Sink Junction Box Wire Connections

Connect the wires in the junction box as follows:

• Twist the bare copper ground wires clockwise together with Linesman pliers.
  - It’s important the wires are twisted together clockwise to match the threads of the wire nut (righty-tighty, lefty-loosey).
  - Linesman pliers have wide short jaws for gripping several wires by the tip of the jaws. The side-cutters are a nice convenience, too.
• Twist on a wire nut to secure the wires.
• Twist and nut the white (neutral) wires together.
• Twist and nut the black (hot) wires together.

Junction Box Wiring with NM-B Cable: Twist the Wires and Secure with Wire Nuts

Do not attach the junction box cover at this time because there is more preparation work to be done.

Wiring the Under Kitchen Sink Receptacle

The Leviton 20 AMP receptacle, single gang metal outlet box, Sigma Electric Double Snap Lock® connector and other end of the flex cable are arranged to wire the kitchen sink outlet. I’ve removed a 1/2 inch knockout on the bottom of the outlet box to receive the Double Snap Lock connector.

3/8″ Metal Flex Cable, Double Snap Lock Connector and Receptacle Box

The NM-B cable is fed through the Double Snap Lock Connector. The snap lock is then snapped on the end of the flex cable until it’s fully seated. The wires and snap lock connector are inserted in the knockout hole and the connector snapped in place. I’ll say it again, I really like the Sigma Double Snap Lock connector.

Metal Flex Cable and Sigma Double Snap Lock Connector

Strip the insulation from the black and white wires using the strip gauge imprinted on the back of the receptacle as shown:

Leviton Electrical Receptacle – Strip Wire Gauge

The Leviton 20 AMP receptacle is back wired per the connection diagram inside the box (yellow arrow). I prefer back wiring when possible because it’s simpler and I like the internal clamping action that secures the wire inside the receptacle. The ground wire is side wired by looping clockwise around the green ground screw.

Wiring the Under Kitchen Sink Electrical Receptacle

I marked and set two drywall anchors in the drywall at the back of the kitchen cabinet to mount the junction box. Here’s a perspective view of the junction box and outlet:

Under Sink Junction Box and Outlet Wiring

I pushed the yellow NM-B 12/2 cable back down into the cabinet bottom to the basement crawlspace to mount the junction box to the drywall anchors with two screws. It was awkward effort because the dishwasher copper water pipe and PVC drain pipe were in the way.

Note that it is in violation of the National Electrical Code (NEC) to place a junction box or outlet on the bottom of the kitchen cabinet. These must be mounted on the wall.

Preparing to Mount the Under Kitchen Sink Junction Box to the Drywall

I mounted the metal junction box to the drywall anchors with two screws (see yellow lines), then held the outlet box against the drywall in a convenient location where it could be reached to plug in the hot water dispenser cord, checked it with a bubble level, marked and set two drywall anchors (see red square). What a pain doing this in such cramped quarters!

Drywall Anchors Set for the Under Sink Outlet

The outlet box is mounted with two screws provided with the drywall anchors:

Under Sink Electrical Box Mounted to the Drywall

I folded the outlet wires into the metal box and mounted the receptacle with the two captive screws. The 4×4 inch metal junction box cover is also installed. Note that mounted the 4 inch steel junction box slightly above the bottom of the cabinet so it wouldn’t get wet in case of a plumbing leak.

Under Kitchen Sink Junction Box and Electrical Outlet

This project is continued in Part 7 where the branch circuit is wired into the ground fault circuit breaker at the main panel.

Take care,

Bob Jackson

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