When you do any major home renovations, you’ll often find your electrical wires are too short to reach the desired location. While you may think you can join two wires together, it is wrong and can cause accidents.
Electrical work is required for various reasons, and home improvement enthusiasts want to know how to do it safely. One of the most commonly asked questions is about junction boxes. Is it possible for extending electrical wire with junction box?
It is possible using a junction box to extend wire, yet you need to comfortably splice two or more wires or cables to the existing wire, and the box needs to remain accessible.
In our guide, you can learn more about adding new wire into your home using a new junction box. By the end, you’ll know enough to add three or more wires to your existing circuit safely.
How Do You Extend The Length Of Electrical Wires?
To make DIY electrical upgrades or simply install a light fixture, you’ll need to understand how to splice wires. (Learn How To Break Up Concrete With Chemicals)
Knowing how to splice wires to your existing wire properly guarantees your electrical repairs and upgrades go smoothly.
Before Splicing Wires
Our instructions assume you’re splicing two Romex wires of the same wire sizes and type together.
Many electricians favor the Romex wire for residential applications. The size and kind of wire are shown on the outer insulation by the markings “12/2 NMC with ground,” which shows a 12-gauge wire with two inner insulated conductors (a black wire “common” and a white wire”neutral”), as well as a non-insulated grounding wire.
Other Romex wire in use for residential construction is:
- 12/3: A 12-gauge wire with three inner insulated conductors and a grounding conductor used on switches and light fixtures.
- 10/2: A 10-gauge wire with two insulated inner conductors and ground used for water heaters.
- 10/3: A ten-gauge wire with three insulated inner conductors and ground used in electric clothes dryers.
- 6/3: A six-gauge wire using three insulated inner conductors and a ground found in electric ranges and ovens.
Splicing Electrical Wires Safety Precautions
Turn off the circuit breaker before working with electrical wires, as electricity can cause serious injury.
How Many Wires Can Be Spliced In A Junction Box?
Any electrical work you do needs checking by a qualified electrician to ensure it is up to code.
Wiring junction boxes can extend circuits, add additional sockets to existing circuits, add lighting points, and carry electricity from one place to another.
They are used to safely link conducting wires or extend a spur from an electrical circuit.
However, if you remove a lot of the protective sleeve from wires, bare live wires can be easily seen and pose a big risk.
The advantage of junction boxes is that all conducting wires and connectors are contained within the box, leaving no exposed wire to be touched or damaged. (Learn How Long Is Paint Good For)
Junction Box Amp Rating
Junction boxes are rated in amps to protect themselves, you, and your home circuit. Make that you have the correct box for the job.
A 30 amp junction box is required for a ring main and a radial circuit, although a lighting circuit requires a 20 amp junction box.
The current of the circuit on which it will be used must be reflected in the rating. A higher amp rated junction box can be used on a lower amp rated circuit, but not the other way around:
- Ring mains and radial circuits = 30 amp
- Lighting circuits = 20 amp
Junction boxes come with three, four, five, or six terminals, so figure out which you’ll need for your project.
The connections are made at the terminals by entering the wire core from either side of the wiring run and then screwing the terminal shut to form a secure electrical connector and join.
A single screw terminal has one connection point where you feed wires in from both directions.
These are commonly found in Standard junction boxes and enable the coupling of a greater range of cable core sizes than the other terminal kinds.
Can I Splice Wires In A Junction Box?
Wires should never be connected outside of an electrical junction box. Junction boxes protect connections from damage and confine sparks and heat generated by a loose connection or short circuit in electrical wiring connections.
Install a box and reconnect the Romex wire inside it if connections aren’t contained in an electrical box.
Other mistakes are often made from how many wires to use and which is the right wire gauge for the job. (Learn How To Turn Off Hard-wired Smoke Alarm)
Here’s a list of errors made and the solutions:
You Cut Wires Too Short
It makes it hard to connect wires if you cut them too short and leave you with poor connections. Leave the wires long enough so that they are at least 3 inches from the box.
Fix: Extend wires
Short wires are easy to fix. First, add 6-inch extensions to the wires that are already there. Then, you can quickly get a wire connector from hardware stores and home centers.
You Leave Plastic-Sheathed Cable Unprotected
It’s easy to damage a plastic-sheathed cable that’s left exposed between the parts of the frame. That’s why the electrical code says that cable should be protected in these places. Wire and cable are especially at risk if they’re run over or under wall and ceiling framing.
Fix: Install a 2 x 2
Nail or screw a 1-1/2-inch-thick piece of wood next to the cable to protect it from damage. If you want to attach the cable to the board, you can use staples. If you run the wire across a wall, you’ll need a metal conduit.
Installing Three-Slot Receptacle With No Ground Wire
Such mistakes can be common, and the fix is also straightforward.
Fix: Install a Two-Slot Outlet
Many people think that if they have two-slot outlets, they should change them to three-slot outlets to plug in three-prong plugs onto the existing wires. But, unfortunately, it needs a ground wire to do this.
Fitting Junction Boxes Behind a Wall
There must be no gaps between the electrical boxes and the wall surface if the wall is made of a material that can catch fire. Boxes hidden behind flammable materials like wood are a fire hazard because the wood is exposed to heat and sparks.
Fix: Use a Box Extension
The only thing that needs to be done is to add a metal or plastic box extension. Then, connect the metal extension to the plastic box’s ground wire with a grounding clip and a short piece of wire.
You Install Cable Without Clamp
People who don’t keep their cables in place can put a lot of stress on the connections. In addition, there are sharp edges on the outside of metal boxes that can cut the insulation on the wires.
Single plastic boxes don’t need internal cable clamps, but the cable must be stapled within 8 in. of the box to keep it in place.
People who use bigger plastic boxes must have built-in cable clamps, and the cables must be stapled inside 1/2 in. of the box. To connect wires to metal boxes, you must use an approved cable clamp. Some junction boxes have a knockout hole, so that positioning could differ.
Fix: Install Clamps
Ensure that the cable sheath is inside the box and that about 1/4 of it is visible inside the box. Some metal boxes have built-in clamps for connecting wires or cable leaving the box. If the box you’re using doesn’t come with clamps, buy clamps and put them in when you add the cable to the box.
You Try to Overfill Electrical Boxes
If there are way too many wires in a box, they can get hot, short-circuit, and even start to catch fire! The National Electrical Code says that boxes must be a specific size to keep this from happening.
Fix: Install a larger box
If you only have two wires in a lower-rated circuit, it is an easy fix. However, it would help if you were sure you have the correct size box for when there are more than only two cables inside.
To determine the minimum box size required, add how many wires and items are inside the box:
- 1 = for each hot wire and neutral wire that enters the box
- 1 = for all your combined numbers of ground wires
- 1 = all your combined cable clamps
- 2 = for each connected device (switch or outlets, although not including light fixtures)
Once you have your total, multiply by 2.00 when using a 14-gauge wire. If you use 12-gauge wire, multiply by 2.25 to determine the minimum box size required in cubic inches.
When you select your electrical junction box, pick a box with at least this much volume.
When checking, you can see plastic boxes have their volume stamped on them. Steel box capacities will be listed in the electrical code as they won’t be labeled. To get the volume, you’ll need to measure the interior’s height, width, and depth.
You Reverse Hot and Neutral Wires
A fatal shock could happen if you connect the black hot wires of an outlet to the neutral wire terminal, which is the other end of the wire.
There should always be a white wire that goes from an outlet or light fixture to the neutral side, which should always be marked with a silver or light-colored screw to show it’s there.
Connect the hot wire to the other terminal. If you have a green or bare copper wire, that’s the ground. So you’ll have a green ground screw that you can connect to, as well as a ground wire or a ground box.
How Do You Extend A Wall Wiring?
If you want to branch off from a current circuit to power a new light socket, disconnect the power and ensure the circuit is isolated before wiring your junction box.
Strip the cables with wire strippers to disclose the cable cores. Don’t strip past the sides of the junction box, as the cable needs to be intact as it enters your junction box. (Learn How To Hang String Lights In Backyard Without Trees)
Try to expose around 1/2 inch of the cable core only. Cover the earth with green and yellow earth sheathing.
You can close the junction box once it has been secured to a secure place and the wiring has been connected to the terminals and checked.
The cover of electrical junction boxes is secured to the base by screwing the securing screw through the cover. To close the junction box cover, adjusting the existing wiring inside the junction box is essential. Avoid forcing the cover shut as you could harm the cables or cause the wire connectors to loosen.