Outdoor Wires: How are they different from Indoor Wires?

Suppose you are an electrician or wiring enthusiast working on your home cables.

In that case, you must choose cables compatible with your work environment.

You can choose between outdoor wires or indoor, whatever type best suits your application. 

Remember, using the wrong type of wire at a place may cause a short circuit, seriously damaging your assets.

Hence, it’s better to understand the difference between wires and their usage.

Let’s look further into the matter. 

Outdoor Electrical Wire vs. Indoor Electrical Wire: Similarities

Here are some similarities between Indoor and outdoor wires.

  • Both types of wires can power up outlets, lights, and electronic fixtures
  • The rating of voltage is around 600V
  • You can find them in standard sizes of 14-2, 12-2, 10-2, and 8-2

Outdoor Electrical Wire vs. Indoor Electrical Wire: Differences

Indoor wires, including connecting bulbs, fans, and power outlets, are best for interior wiring.

On the other hand, outdoor wires are designed to endure high temperatures and extreme weather. Hence, they differ in construction as well. 


Outdoor wires must withstand humidity, temperature, and moisture changes.

Also, these conditions can be extreme, so the wire should have thicker insulation that can protect the inner wires even though it may cause the cable to be slightly bigger.

Plug Style

Plugs can be three-pronged or two, depending on the type of appliance it is connected to.

In indoor wires, you can observe both types of plugs, two for small appliances and three for heavy machines.

For outdoor wiring, you will usually observe that it has a ground prong attached, making the switch three-pronged since there is a high chance of a short circuit. 


Indoor wires are thin and shorter since they don’t have to pull too much power.

On the other hand, outdoor wires are thicker as they have heavy power use. Also, they may be longer. 

Power Use

Indoor wires are found with devices that use low voltages and have lesser power consumption.

You will use heavy outdoor wires for power tools and larger lighting fixtures outdoors. 

Electric Code Requirements

There are different electrical requirements that every location complies with.

Hence, you have to choose the cables that are according to the safety standards of that area.

These wires have protective ratings that should match the appliance’s needs. 

Outdoor Electrical Wire vs. Indoor Electrical Wire: Pros and Cons

Outdoor wiresCan withstand high temperatures and abrasive environments better than indoor cablesHeavier on the pocket and you need the expertise to install them in places
Indoor wiresCheaper and easier to install in places than outdoor cablesNot suitable for outdoor usage and thus, it’s not advisable to use them in water and other factors.

What Type of Wire Should You Use Outdoors?

Outdoor cables covered in Ice

Caption: Outdoor cables covered in Ice

In an outdoor environment, you are exposed to water, direct sunlight, continuous footsteps, and other harsh conditions.

To conquer them, you need heavy protection over your wires so they don’t deteriorate early.

Here are some popular outdoor wires for your next outdoor project. 

Type UF-B

UF stands for Underground Feeder cables, which can be directly buried underground without any conduit.

As for the B in the name, it shows that the cable is used for branched circuits. These cables have PVC jacketing with colored PVC and nylon insulation.

Also, the conductor can be either strand of copper or solid wire with bare copper grounding wire. 

You can also use UF-B wires where corrosion resistance is necessary for indoor applications.

Furthermore, these cables can support 600V, 90-degree Celsius temperature and are available in AWG. 

Type MC

In Type MC cables, THHN or THWN insulation can make it best for many outdoor applications.

The MC, short for Metal-Clad, means that these cables have aluminum armor surrounding the insulation, which helps transfer the current in harsh environments. 

MC cables in stranded, solid, bare copper types with sizes of 2 to 14 AWG.

Also, you can use them over the ground outdoors or underground with a conduit. 


SE-R cables are round service entry wires that use THHN insulation with PVC jacketing and ground wires.

These cables can resist UV rays of sunlight and moisture and, thus, are best for panel feeders or branched circuits. 

Although it is not good for direct burial, you can use them in conduit.

Also, these cables can work at 90 degree Celsius in dry/wet conditions and are available in 6 to 4/0 AWG. 


USE-2 wires have aluminum or copper wires and rubber insulation that protects from high temperatures, abrasions, UV light, chemicals, moisture and pressure.

Hence it has proven best for outdoor solar projects for its durability. It also features 90-degree Celsius temperature resistance and 600V support. 

What Type of Wire Should You Use Indoors?

Wiring inside walls

Caption: Wiring inside walls

As compared to outdoors, indoor wiring does not face hard conditions.

Taking advantage of the matter, you can choose thin wires that will cost you less and are easy to install.

Although not heavy, it also features some degree of insulation to rule out any possible problems in the future.

Below are some common indoor wires. 

Romex NM-B

Romex wires are a one-stop solution for many residential and small building wiring as it is best for branch circuits.

They have special jacketing that you can easily pull through the conduit.

Also, they feature a nylon jacket with PVC insulation and support 90 degree Celsius temperature for dry use.

It is available in 8 to 14 AWG and is similar to UF-B but has low protection. 


THHN stands for Thermoplastic High Heat and Nylon Jacket, and THWN is its water-resistant version.

These wires have color that indicates their hot, neutral, and ground purpose. You can use these wires in electrical boxes and outlets of your home.

Also, these wires come in large gauges to facilitate high power usage. 

Low-Voltage Wire

For some applications, you will find low-voltage cables like speakers and thermostat wires in your home.

These cables have a smaller size and little insulation. However, specifications can change with applications. 

Direct-Burial Wires vs. In-Conduit Installation for Outdoors Wires

Outdoor wires categorize into direct-burial and conduit wires. 

Direct burial wires can be installed underground without any conduit.

These cables have durable insulation that protects against moisture and other harsh conditions.

Hence you can bury these cables without conduit for a 24-inch cover, while others might need 6 to 18 inches. 

However, some cables do need conduit since it may be necessary for the environment you are working in.

For example, you can use PVC conduit for areas where corrosion is expected.

All and all, it would be best if you looked for all the ratings and listings for appropriate installation. 

Rules for Outdoor Cables and Conduits

Cellar of an electric station

Caption: Cellar of an electric station

Outdoor installation of cables and conduits should be under the following rules.

  • While using exposed wires, see that it lists the application you are using. 
  • You can directly bury the UF cable with a 24-inch cover without a conduit. 
  • Backfill surrounding conduits should have smoother granular material without rocks. 
  • Have 6 inches of earth cover on wires that you bury under rigid material RMC or intermediate metal IMC conduits.  On the other hand, PVC conduits need 18 inches of earth cover.
  • Bury low voltage wires are 6 inches deeper in the earth. 
  • Hand the wires 22 or more feet above the area with a hot tub, spa, pool, etc.
  • Also, hang the data transmission cables 10 feet above the pool, spa, or tub surface. 
  • Wires running transmission from under to above ground should also have conduits to protect it from the depth to the termination point. 


Outdoor and indoor wires have different specifications, and each is made for different applications.

Using one instead of another may be unnecessarily expensive or even result in hazardous conditions.

Hence, it’s best to analyze the area and then choose the type of wire to install.

At Cloom, we offer wire harnesses for outdoor and indoor usage, with expert analysis and design. 

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