Today I’m installing the vanity light and switch. The main effort is pulling the new wire through the walls, wiring in the new junction boxes and wall switch.
This photo points out the new vanity light bar and wall switch. You can also read Part 13 of this project which covers the vanity installation and plumbing connections.
The following photo is the situation before I started the job – compare with the finished job above.
Basement Bathroom Vanity Light Electrical Wiring
The key materials needed for this project are (from left to right):
- Light switch – I chose the square rocker style.
- “Old work” junction box for the light switch.
- Metal “new work” square junction box with cover.
- NM cable connectors (brown bag).
- Round “old work” junction box for the vanity light bar.
Educate yourself before working with electricity and know the basics of the Building Code requirements. You can get yourself shocked, killed and/or burn down the house. If you’re unsure or uncomfortable with electricity and residential wiring, hire a licensed electrician.
Before you begin:
- Identify your the electrical wiring configuration. Know which wires are connected back to the main electrical panel and which are branch extensions.
- What is the existing load on the circuit you plan to use for the new line extension? If there are too many devices (loads) on the circuit, you may need to run new wiring back to the main electrical panel and install a new circuit breaker.
- Make a wiring diagram of the “current state” and “future state” (a.k.a. before and after). This will help to prevent getting your wires crossed. (Pun intended).
- Turn off the power at the main electrical panel by switching off the circuit breaker. Is the power off? Check the circuit with a test probe or meter. Are you sure it’s off? Check again.
Before and After Bathroom Wiring Diagrams
This is wiring diagram for the bathroom before I started work. I was lucky that the GFCI outlet was on a “home run” circuit back to the main electrical panel and had just one branch circuit to the other wall outlet beside the sink. Click on the diagram for a full size view.
The new wiring diagram is illustrated below. The changes I had to make are:
- Install a junction box in the ceiling crawlspace to make the various new circuit connections.
- Remove the original wiring to the GFCI outlet and run a new line from the junction box to the GFCI. It’s necessary to remove the original wiring because there wouldn’t be enough slack to make the new splice connections at the junction box when I cut the wire in two.
- Install the junction box for the light switch and run a new wire.
- Install the junction box for the vanity light and run a new wire.
Click on the diagram for a full size view.
I shut off the circuit breaker and disconnected the line side wires (i.e. coming from the electrical panel) from the GFCI outlet. The line side wires are at the top of junction box.
Line side wires (top) disconnected. The load side (bottom wires in wall box) feed the 2nd electrical outlet by the sink.
Construction string is duct taped to the line side wires. The line side wires will be pulled up from the ceiling crawlspace and cut to provide power to the junction box in the ceiling crawlspace.
Old Work Junction Box Drywall Cutout
Before pulling the line side wire into the ceiling crawlspace, I measure and cut a hole in the drywall for the light switch junction box. A carpenter’s level is used to ensure the box is plumb and the outline traced on the wall with pencil.
This is the position of the light switch box traced on the wall, ready to be cut out with a Rotozip spiral saw.
The cutout for the light switch junction box. The Rotozip cuts drywall like butter.
Pulling New NM-B 14/2 Electrical Cable
This is a key point - the line side wires from the GFCI are pulled out of the GFCI junction box and out of the hole for the light switch as shown below. The reason is the new wire run for the light switch will be pulled with the old line wire into the ceiling crawlspace. If you miss this point, you’ve created significant extra work for yourself because you’ll have to fish the light switch wires from scratch.
The new run of NM 14/2 electrical wiring (that’s Non-Metallic 14 gauge, 2 conductor with ground wire) for the light switch is duct taped to the GFCI line side wires. The wire is being spooled from a box (not shown).
Working now in the ceiling crawlspace above the bathroom, this is the line side wire that will be pulled up from the GFCI outline with the new wire for the light switch.
After removing a wire staple inside the wall above the GFCI junction box, I was able pull the new light switch wire into the attic crawlspace with the construction string. The old line side wire is to the left of the duct taped joint.
Ceiling Electrical Junction Box Installation
A metal junction box is used for the splice connections in the ceiling crawlspace. NM cable connectors will protect the wires from the sharp edges of the knockout holes and clamp the wires in place for strain relief.
Four knockouts are removed from the junction box, one for each of the new wire legs per the wiring diagram. NM connectors are installed and the junction box fastened to a ceiling joist with two wood screws.
Bathroom Ceiling Junction Box Wiring
The old run of line side wire cut to length and mounted to the junction box as shown. A new length of NM 14/2 wire is duct taped to the construction string to be pulled to the GFCI outlet.
The new run of wire pulled down through wall and out of the GFCI junction box. This is why the construction needed to be pulled up with the old line side wire from the GFCI, such that the new wire could be pulled back the same pathway – thereby avoiding tedious job of fishing a new wire. Also, the new wire for the light switch is hanging out of the hole in the drywall.
Next, a generous length of new wire is spooled off in the ceiling crawlspace to reach the vanity junction box that I’ll install shortly.
The four wires are labeled as shown with permanent marker and clamped to the junction box. About 8 inches of wire extends inside the junction box to make the splice connections.
Following the wiring diagram, the ground wires are twisted and nutted together. I generally make the ground connections first for safety. I’m using nuts rated for four (4) to six (6) individual 14 gauge wires.
Per the wiring diagram, the hot wires for the 1) line side, 2) GFCI outlet and 3) vanity light switch are twisted and nutted together. You can see why labeling the wires with permanent marker is so important to keep track of everything. The white (neutral) wire from the vanity light switch is relabeled as hot by coloring the end with a black permanent marker. You can also relabel a neutral white wire as as “hot” by wrapping it with a black electricians tape.
The hot wire to the vanity light and return hot wire from the light switch are nutted together as shown below.
The remaining neutral (white) wires are twisted together with needle nose pliers and held with a wire nut. Remember, “righty-tighty and lefty-loosy” when twisting and nutting wires.
Tightening the wire nut on the neutral (white) wires.
Bend and fold the nutted wire connections into the junction box such that the metal cover can be attached as shown:
Metal Junction Box Ground Screw
Almost forgot to install the #10-32 green ground screw and ground wire in the steel electrical junction box (see the red arrow). Metal junction boxes must be grounded per the National Electrical Code (NEC). The junction box ground wire is taken from a scrap section of NM-B 14/2 cable, looped around the #10 ground screw, then twisted and nutted to the other ground wires. The #10 green ground screw is not included with the junction box and available in a package of 10 for about $1.
The lid is attached to the junction box with the two screws provided with the box.
The new wires are fastened within 12 inches of the junction box with insulated electrician’s staples. The staples should be hammered in just enough to prevent the wire from slipping, but not so tight that it pinches the insulation or kinks the wire.
Here’s a look back at the ceiling crawlspace and the location of the junction box. I fastened a piece of plywood to the ceiling joists so I’d have a place to sit while wiring up the new junction box. This simple plywood seat made working in a cramped space much more tolerable. Click on the image for a full size view.
GFCI Electrical Outlet Wiring
With the crawlspace wiring completed, work moves back to the bathroom. The GFCI ground connection is made with a “pigtail” (short piece of wire) to the line- and load side grounds and nutted together.
The line side hot and neutral wires are “backwired” to the GFCI outlet. I prefer backwiring when possible because it’s neater and a bit quicker. “Backwiring” means the outlet is designed with small holes for the wires to enter through back of the outlet that are captured by a screw-down clamp. I recommend back-wiring only on quality outlets that use the screw and clamp system as shown here. If in doubt, side-wire the outlet in the traditional way by wrapping the wire around the screw in a clockwise direction (i.e. “righty tighty”) and tighten the screw firmly down on the wire.
In Part 15 of this series, the the light switch and junction box for the vanity light are wired.
Be careful and take care,
Copyright © 2013 HandymanHowTo.com Reproduction strictly prohibited.