How-To Electrical
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Trans 1) Getting Started Trans
2) Electrical System Basics
3) Service Panel
4) Running Cable
5) Outlets
6) Switches
7) Installing Light Fixtures
8) Common Electrical Codes
9) Replacing Switches & Outlets
10) Repairing Lamps & Cords
11) Glossary

Installing Outlets

wiring illustrationMost switches and outlets are installed after mechanical rough-ins, drywall and paint are completed.

When you shop for devices like switches and outlets, there are several different types to wade through. Make sure to get the device that works properly with the circuit.

The type of switch you install is determined by the circuit's wiring scheme. Outlets are pretty standard, but GFCIs are required in some rooms and box size is another thing to consider.


Sizing Junction Boxes

electrical junction boxAll switches and outlets (receptacles) need a properly-sized junction (electrical) box. For example, a 2" x 3" box with 3 wires (14 gauge) should be 2 1/2" deep. The same box with 5 wires must be 3 1/2" deep.

Installing an undersized box is probably the most common wiring mistake for do-it-yourselfers. When in doubt, it's usually best to use a larger box.

If you're not sure about box size requirements, remember to ask your electrical inspector when submitting diagrams.

Here's one way to calculate minimum box size:

junction box with wires inside1. Count the number of wires for the box. Don't count outlet/switch pigtails and count all ground wires as one.

2. Take that number, add one for each cable clamp, and two for each device (like a switch or outlet).

3. If the box contains only 14-gauge wires, multiply the total by 2 cubic inches. Or, for 12-gauge wires, multiply the total by 2.25 cubic inches.

The result is the minimum allowable volume the box should be. Volumes are usually stamped into the back of the box on the inside.


GFCI Outlets

GFCI Outlets with single pole switchA GFCI (Ground Fault Circuit Interrupter, also GFI) is an outlet designed to prevent electrical shock. It's a little bigger than a normal outlet and has two buttons on the front.

These buttons allow you to check the GFCI monthly to see if it's still working properly. Push in the black "Test" button to kill power to that circuit. Restore power by pushing the red "Reset" button.

A GFCI also monitors the current being used by anything plugged into it. Normally, a balance of current passes through the GFCI.

back side of a standard GFCIIf a misdirection of current, called a "fault to ground," the GFCI senses it and shuts down almost instantly -- which can prevent potentially hazardous shocks.

On the back side of a standard GFCI are four (two sets) terminal screws -- two brass "hot" screws and two silver "neutral" screws.

The bottom brass and silver set -- marked "Line" -- is for incoming wires. The top set -- marked "Load" -- is for wires going to other protected outlets.

The GFCI also has a green "ground" screw on the bottom. That's where the bare copper ground wire connects and provides a path for dangerous current to be safely diverted.

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