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are metal or plastic enclosures used as housings for wiring connections. The connections within are called branch circuits and usually represent the end of a conduit run. Junction boxes make wire access easy, since all one must do is remove the covering to make alterations, repairs, or additions to a conduit. Junction boxes also protect wiring from the elements or environment, which can sometimes be corrosive or otherwise harmful to wiring material. Finally, junction boxes protect wiring from unwanted tampering, whether malicious or unintentional.Junction Box Wiring Basics
Essentially, a junction box houses wire connections in order to split off power from a single source to multiple outlets. For instance, a
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might contain one wire power source that is connected through multiple wires to power several different lights.Junction boxes are usually between 2 ½ to 3 ½ inches long and made of metal or hard plastic. The functional difference between plastic and metal depends whether or not the junction box is supposed to support any weight. Some metal junction boxes can support light fixtures; plastic junction boxes cannot withstand this weight. Additional differences include installation, in that plastic junction boxes are typically quicker and easier to install than metal ones. However, a standard junction box designed to simple cover wire splices can be either metal or plastic.
Wire Splices in Junction Boxes
All wire splices must be contained within a junction box for a building to meet electric code, although sometimes splices are missed and may present hazards as a result. Any exposed wiring can be dangerous, but exposed wire splices are especially prone to accident because they can be tripped over, expel sparks or misrepresent themselves be misperceived as playthings by children or pets.
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are helpful for wire splices because they also allow one to easily locate the wire splice area.Instructions
Shut off the Power and Test the Wires
Turn off the power to the circuit you'll be working on by switching off the appropriate
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in your home's service panel (circuit breaker box). Test all of the wires you'll be working on with a non-contact voltage tester. The test should confirm that no voltage is present in any of the wires.Set up Clamps for Each Cable
Install a cable clamp for each cable, as needed. Standard plastic
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do not have knockouts and contain internal cable clamps. Metal boxes usually have internal clamps; if yours does not, install a locknut-type clamp for each cable. Insert the threaded end of the clamp through a knockout hole and secure the clamp inside the box with the ring-shaped nut. Tighten the nut with pliers.Secure the Cables
Feed the cables through the clamps and into the box. The cable sheathing (outer jacket) should extend 1/4 to 1/2 inch into the box beyond the clamp, and the individual conducting wires should extend about 6 inches into the box. If necessary, trim the wires as needed and strip 3/4 inch of insulation from the end of each wire, using wire strippers.
Secure the cables by tightening the screws on the clamps, being careful not to overtighten and damage the cables. Plastic boxes usually have spring-tabs for clamps and do not require tightening.
Join the Wires
Join the wires together with approved wire connectors, following the manufacturer's instructions:
Join the bare copper (or green insulated) ground wires together first. If the box is metal, add a pigtail—a 6-inch length of the same type of ground wire—to the ground wire connection, then connect the loose end of the pigtail to the ground screw on the box. Special green wire nut connectors are generally used to join the grounding wires together.
Join the white (neutral) wires together, then join the black (hot) wires together, using a wire nut or other approved connector for each wire pair. If there are red (hot) wires, join them together, as well. Confirm that all wires are secure by gently tugging on each wire.
Finish the Job
Carefully fold the wires into the box. Install the box cover, securing it with two screws. Code requires that the cover must be a solid "blank" without holes. Restore power to the circuit by switching on the circuit
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