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Know Your Electrical System: The Junction Box

Look around your house and notice the plastic or metal cases that are connected to the wirings of your electrical fixtures. You may have seen these electrical boxes a couple of times but you just don’t know what they’re called and what they’re for. You just know that they’re part of your electrical wiring system.

Today’s your lucky day because we might have something to add to your vocabulary: junction box!

What is a Junction Box?

The junction box is an electrical casing that houses and protects your circuit cables and wires. These encased wires are called ROMEX and they come in various colours such as black for hot wire, white for neutral, and green or copper for grounding wire. The junction box is the safe zone where ROMEX wires coming from the main electrical panel meet those wirings that proceed to various electrical outputs such as switches and plug sockets.

Standard junction boxes measure 2.5 inches by 3.5 inches which can be made of metal or plastic material such as PVC, ABS, or fibreglass. They can be found around your house or building affixed to framings which contain the merging of two or more electrical wires. 

Junction boxes have a detachable cover which must be always accessible in case you need to alter your electrical wirings.

What’s a Junction Box for?

The junction box has various uses but they’re mainly for branching out power from the main electrical panel to multiple outlets or fixtures. This means that you don’t have to employ long cables to connect your electrical fixtures to the main electrical panel because the junction box makes it possible by splicing these wires.

Aside from this, the junction box is also used to:

  • protect wire splices from dirt and dust, moisture, and animals such as rats and mice from chewing on your wires
  • locate electrical wires easily
  • prevent wire tampering
  • stop fire inside the junction box from spreading

Factors to Consider

When working on your junction box at home, it is important to think through these factors:

  • Protection value
  • Type of wire connections and the number of terminals
  • Material that makes up the junction box
  • Size and shape

Installing a Junction Box

When installing a junction box, it is ideal and safer to connect a new ROMEX wire from the main electrical panel to the junction box instead of just working on an existing electrical box. This way, you are preventing a short circuit from happening which can cause a fire.

Before you work on your junction box (or anything electricity-related), make it a habit to take safety precautions first and turn off the main power. After which, you can begin mounting your box to a sturdy and accessible framing. Pull in all the spliced wires separately through the holes called knockouts in metal boxes and then clamp them using cable clamps in plastic junction boxes. 

Strip ¾ insulation at the terminal portion of each wire and then twist the cables together starting with the green or copper ground wires, and then the white neutral, and lastly, the black live wires. You have to make sure that same-coloured wires have the same diameters. Finally, cover your junction box tightly and securely.


Because working with wires is a challenging task, it must be noted that you should work carefully and expertly. Aside from this, poorly set up junction boxes can cause house fires and damage to properties. While installing and working with junction boxes can be a DIY job, surely, you wouldn’t risk your life or property for your electrical project.

Sydney Eastern Suburbs Electrician can work with your junction box for you. We have great a team of licensed and professional level 2 electricians that are capable to all your electrical needs. We are around Sydney to manage your electrical problems from the most basic to more complex electrical work. We ensure your safety and the integrity of your electrical wiring system.

Want us to help you install and alter your junction box for you? We’re open 24/7! Contact us now at (02) 8378 2827.

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