Can You Leave Extension Cords Outside?

The emergency generator has an electric start that depends on the battery having power. I need to run an extension cord from the house to the shed if I want the electric start to work. So I wondered if it would be safe to leave an outdoor extension cord outdoors for the whole winter.

An outdoor extension cord is highly resistant to weather, but it’s not going to last forever in snow, ice, rain, and wind. Outdoor cords do withstand these elements for years, but will eventually win out over the cord’s strength. Use an outdoor extension cord for as long as you need it. When you’re done with it, bring it back to a warm, dry place.

Internationally, bad extension cords cause 50,000 fires and 490 deaths every year.

A bad extension cord is one that:

  • is overloaded
  • is the wrong size,
  • is fully loaded without a break in service,
  • is unable to vent its heat (something is on top of it)

Outdoor extension cords are only safer than indoor cords. They’re not indestructible. They do not put a force field around your vulnerabilities.


I am a homeowner and a researcher. I am not an electrician. I present this info with care, however, only an electrician can give you definitive extension cord solutions.

Can You Use Any Extension Cord Outside?

Watt's Wire outdoor extreme extension cord

You would think that an “outdoor” extension cord would be perfectly safe outside.

An undamaged outdoor cord is safe outside, it’s just not perfectly safe.

A good outdoor cord will last for years, even if it lives outside 24x7x365.

It’s just that its useful life will last a lot longer if you give it a occasionally lower its load, or bring it into a warm area..

Dangers include animal bites, debris in the outlet, water and abrasion damage. The sun can crack the outer jack, and vehicles rolling over them do not help the cause.

Protecting it in a warm, dry place will extend the cord’s useful life.

What is the Difference Between Indoor and Outdoor Extension Cords?

Outdoor extension cords have thicker electrical wires and thicker jackets.

The jacket has a “W” printed on it indicating it’s designed for outdoor use.

The “gauge” refers to the thickness of the internal wires that carry the electricity.

When wire gauge, thicker is better as it safely carries more electricity.

Well, someone from Bizarro World decided to make wire gauge meanings a bit of nonsense, so you need to understand how to reverse your thinking.

The higher the gauge, the weaker the wire. The lower the gauge, the stronger the wire.

The strongest household wire is 10 gauge. A heavy dut outdoor extenions cord is usually 12 guage.

Which Part Conducts Electricity?

Watt's Wire cords are 12 gauge

The wires inside the jacket conduct the electrons from the wall to the tool or lights.

The extension cord jacket is the rubbery coating surrounding the wires.

The thicker and stronger the jacket, the more protection it provides the wires inside.

This jacket protects the inner wires from rain, snow, and sunshine.

Never use an extension cord with a broken jacket.

You might get a shock or risk a fire.

How to Tell if an Extension Cord is for Outdoor Use

The US government requires extension cord manufacturers to place the letter “W” on cords designed for outdoor use.

Use only “W” cords outside.

When you use a “W” cord outside, you should plug it into a GFCI (Ground Fault Circuit Interruption)  outlet.

Modern codes require a portion of outlets in homes be include GFCI outlets.

The GFCI outlets have built-in circuit breakers that switch off power flow when input and output power does not match.

In other words, if the cord’s wires get wet, the electricity flow will become unbalance (and unsafe). The circuit breaker shuts down the electricity flow to prevent a shock or fire.

When Do You Need an Outdoor Extension Cord?

Use an outdoor rated “W” extension cord for all electrical cord use outside. Just don’t use an indoor cord outside.

Use an outdoor extension cord for every outdoor electrical connection

Even if you are just doing something in the garage, use an outdoor extension cord.

Suppose you brought an indoor cord outside to recharge a weed whacker.

You would leave the tool while it charged.

Maybe you come back later, and need a cord to run the hedge trimmer.

The battery is full, so you can take the cord. That is easier than going inside to get the “outdoor” extension cord.

You take the indoor cord and use it outside.

Now the phone rings inside, so you leave your project.

You need to pick up your kids. The indoor wire is outside. You leave it “just for a moment” while you run the errand.

Are you seeing where this is going?

There is just no point in taking an indoor cord into the garage.

It is too tempting to use that indoor cord on an outdoor project. This is why you risk electric shock and a fire hazard.

Use an outdoor extension cord to:

  • run power from the garage to the outdoors
  • light Christmas lights
  • run electric yard tools
  • recharge yard tool batteries
  • run security cameras
  • run temporary lights

Consider hiring an electrician to hard-wire your security cameras and lights.

Use an electrician to wire security cameras and outdoor lights.

Outdoor cords are tougher than indoor cords, but they are not indestructible.

Are Outdoor Extension Cords Dangerous?

Outdoor extension cords are dangerous if they are not to required specifications or if they are damaged.

That damage can include water getting inside the female end, a break in the jacket, or the prongs getting loose.

This guide (PDF document, opens in new browser window) will teach you how to avoid fires, lacerations, burns, and shocks. Learn how long a cord can be before it is unsafe.

How to Make Using an Outdoor Extension Cord Safe

Stage the cord so that it is not a tripping hazard. Run the wire along the building structure.

Inspect the wire for jacket damage.

Do not use an extension cord if you can see its internal wires.

Are Outdoor Extension Cords Waterproof?

Before using the hosue, find the outlet end. Check it for water. Dry it if necessary.

For regular maintenance putx dielectric grease in the receptacles to keep water out.

Assume high danger near water.

Water and electricity can be lethal.

Talk to an electrician about the use of electricity near pools, ponds, or other bodies of water.

Is it Safe to Connect Two Outdoor Extension Cords Together?

You can connect two wires, but it is safer to buy one long one.

If you do connect to extension cords, use a rain guard to protect the connection from the elements.

A rain guard is a box you put over the two ends where they connect to each other.

What is the Gauge of an Outdoor Extension Cord

There is more to this subject than what is below.

Re-read the safety presentation for more information.

Gauge does not affect the cord’s indoor/outdoor rating.

A 12-gauge wire carries a heavy load both inside and outside the home.

A 20-gauge wire can handle only small jobs, but is OK to use if it’s in a “W” jacket.

The changes of a 20-gauge cord being useful outdoors are small.

Use a 16-gauge cord for lamps, fans.

Use 12 gauge for the garage vacuum cleaner and table saws.

What is the Best Outdoor Extension Cord?

I like this brand. It’s higher quality than any other I’ve found.

Click here to view.