Learning, Wiring,

How Much Wire to Leave in an Outlet Box?

In this article, ill teach you how much wire to leave in an outlet box.

Too much wire inside an outlet box can overheat wires and it could lead to an electrical fire. Short wires might cause those wires to break. Is there a middle ground for all of this? Yes, you can avoid the above situations by acting according to the NEC code. If you aren’t familiar with it, ill teach you more below.

In general, you should leave at least 6 inches of wire in the junction box. When the wire is in a horizontal line, it should come out 3 inches from the opening, and the other 3 inches should be inside the box.

I’ll go into more detail below.

The Ideal Wire Length to Leave in an Outlet Box

Leaving the right amount of electrical wire length is crucial for the safety of the wires.

For instance, shorter wires might break due to stretching. If the outlet is located in an area that has freezing temperatures, shorter wires can be a problem for you. So, consider all this before completing the wiring for an electrical outlet.

NEC Code for Wire Slack in a Box

measuring wires in outlet box with tape
Video | Backyard Maine

According to NEC, you should leave at least 6 inches of the wire.

This value depends on one factor; the depth of the outlet box. Most outlet boxes have a depth of 3 to 3.5 inches. So, leaving at least 6 inches is the best option. It will give you 3 inches from the opening of the box. The other 3 inches will be inside the box, given that you leave a total of 6 inches.

cut off extra wires in outlet box
Video | Shopfix

However, leaving 6-8 inches of wire length is the most flexible option if you use an outlet box with a higher depth. Leave 8 inches for an outlet box that has 4 inches of depth.

Be mindful of: When using metal outlet boxes, remember to ground the outlet box. Use an insulated green wire or a bare copper wire for this.

How Much Extra Wire Can I Leave in My Electrical Panel?

Leaving extra wire in the electrical panel for future use is not a bad idea. But how much?

Keep just enough extra wire and place it on the edge of the panel board.

Leaving too much wire inside the panel might cause overheating. This overheating issue is only related to constantly current carrying wires. There are lots of harmless cables inside the main electrical panel such as ground wires. So, you are allowed to keep a considerable amount of ground wires but never leave too much. It will mess up your electrical panel.

There are codes for these questions. You can find them in the following NEC codes.

  • 15(B)(3)(a)
  • 16
  • 20(A)

Be mindful of: You can always splice wires when more length is required.

Electrical Safety Tips

We cannot ignore the safety issues of electrical boxes and wires. So, here are some must-follow safety tips.

Too Short Wires

Short wires might break or cause poor electrical connection. So, make sure to keep a suitable length.

Keep the Wires Inside the Box

All the wire connections should be inside the electrical box. Exposed wires can electrocute someone.

Ground the Electrical Boxes

When using metal electrical boxes, ground them properly using a bare copper wire. Accidently exposed wires might transfer electricity to the metal box.

Too Many Wires

Never put too many wires inside the junction box. The wires can heat up pretty quickly. So, overheating can lead to an electrical fire.

Use Wire Nuts

Use wire nuts for all the electrical wire connections inside the electrical box. This step is an excellent safety precaution. Also, it will protect wire strands to a great extent.

Be mindful of: Whenever dealing with electricity, follow the necessary safety precaution to protect you and your family. (1, 2)

Take a look at some of our related articles below.

(1) electricity – https://ei.lehigh.edu/learners/energy/readings/electricity.pdf
(2) protect you and your family – https://blogs.cdc.gov/publichealthmatters/

Video References


Everyday Home Repairs

Backyard Maine

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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