What kind of electrical wire do I need for outside?
Understanding Different Types of Electrical Wire and How to Choose the Right One
Electrical wires, made primarily from copper or aluminum, are insulated conductors that transfer electricity throughout your home. Choosing the correct wire or cable when installing new wiring is crucial.
When inspecting older wiring, identifying the wire type can reveal much about the associated circuit, crucial for tasks like identifying connections within a junction box. Modern home wiring has become standardized, with homes built post-mid-1960s often featuring similar wiring types.
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Below is an overview of different types of home electrical wires to help you choose the right one for safe and accurate electrical projects.
Tip
Once you identify your home's wiring type, consult local building codes before attempting new installations. New electrical installations require wiring that complies with local regulations.
Wiring Terminology
Understanding basic wiring terms is essential. An electrical wire is a type of conductor, typically made from copper or aluminum (or copper-sheathed aluminum), either in solid or stranded form.
Most home wiring is insulated with a nonconductive plastic coating, except ground wires, which are usually solid copper and may be insulated with green sheathing or left uninsulated.
Warning
Larger wires in your home often carry 120- to 240-volt circuit voltage, known as line voltage, which is dangerous. Lower voltage wires are less dangerous but should still be treated with caution until confirmed safe.
What Kind of Electrical Wire Do I Need for Outside?
Choosing the correct wire for your electrical needs, especially for outside, requires understanding the differences between indoor and outdoor wires. Each is designed for safety and optimal performance in their respective environments.
Indoor vs. Outdoor Wire: Points of Comparison
Indoor and outdoor cables have specific features suited to their environments, whether it's the gauge or insulation. Here’s how they differ:
Applications
Outdoor wires are crafted for landscape lighting, outdoor outlets, and underground circuits, needing to endure elements like moisture and temperature variations. Indoor wires are meant for connecting appliances and electronics within controlled environments.
Insulation
Outdoor wires have robust insulation to protect against moisture and weather. Common insulation materials include cross-linked polyethylene (XLPE) and thermoplastic elastomers (TPE), chosen for their durability. Indoor wires usually feature lighter insulation like polyvinyl chloride (PVC), suitable for less demanding environments.
Gauge
Outdoor wires often use a thicker gauge to prevent power loss over longer distances, while indoor wires can be thinner due to shorter distances.
For example, Romex, a common indoor cable, comes in sizes like 14/2, 12/2, or 10/2. Service entrance cables, used for higher power demands, are classified by gauge sizes, such as 4/0 for 200-amp services.
Flexibility
Outdoor wire must be flexible to navigate tight spaces and obstacles. Indoor wire flexibility varies depending on the application.
Labeling & Certification
Outdoor wires have UV-resistance certifications and often follow standards like UL. Markings like "Sun Res." or "UV" indicate suitability for sunlight exposure. Indoor wires typically lack these certifications as they are not exposed to harsh conditions.
Visual Identification
Outdoor wires can be identified by specific markings like:
- "UF" for Underground Feeder, suitable for direct burial.
- "Sun Res." or "Sunlight Resistant" for sunlight exposure.
- "Wet" or "W" for wet locations, like "THWN" indicating wet location suitability.
Indoor wires often have different markings like "NM" or "NMB" for non-metallic sheathed cables, commonly used in residential wiring.
Physical Characteristics
Outdoor wires have thicker insulation to withstand environmental conditions, while indoor wires have thinner insulation suited for controlled environments.
Color
Outdoor wires for direct burial may be gray, while indoor wires come in various colors, indicating different electrical roles. However, do not rely solely on color; always check other markings.
Safety Considerations for Indoor and Outdoor Wire
Using the correct wire type for indoor or outdoor applications ensures safety and longevity. Mixing these wires can pose several risks.
Outdoor wires, with their heavy insulation, are robust but costly and difficult to work with indoors. Conversely, indoor wires used outdoors can deteriorate due to exposure, leading to hazards.
Consult local electrical codes to ensure indoor and outdoor wire use complies with regulations. Some wires, like THHN/THWN and XHHW, are versatile for both environments with proper protection.
Types of Outdoor Cables
Outdoor cables are designed for different conditions and applications:
UF-B (Underground Feeder - Direct Burial)
Designed for underground use, UF-B cables have solid insulation perfect for residential wiring, outdoor lighting, and landscape projects, typically featuring a PVC jacket.
USE-2 (Underground Service Entrance - Direct Burial)
Known for resistance to sunlight and moisture, USE-2 cables are used for utility services and solar installations, often without needing conduit.
RHH/RHW (Thermoset Insulated)
RHH/RHW cables have thermoset insulation suited for high temperatures and harsh conditions, commonly used in industrial settings.
Mobile Home Feeder
These cables supply power to mobile homes, offering high ampacity and resistance to sunlight and heat.
URD (Underground Residential Distribution)
URD cables are used for direct-burial power distribution, ideal for residential and commercial areas.
PV Cable (Photovoltaic Cable)
PV cables are UV-resistant and flexible, designed for solar power applications.
Types of Indoor Cables
NM-B Romex (Non-Metallic Building Cable)
NM-B Romex cables are flexible with multiple insulated conductors and a grounding wire inside a non-metallic jacket, used widely for residential wiring.
Low-Voltage Wire
Flexible low-voltage wires are used for devices like doorbells and security cameras, available in configurations like twisted pair and coaxial.
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