The Ultimate Guide to Junction Box Material Selection

A junction box is essential for protecting your electrical connections and wire splices. It shields them from elements and potential hazards, reducing electrical risks. In this guide, you’ll learn about the typical materials, their benefits and drawbacks, and how to pick the best junction box for your needs.

The Ultimate Guide to Junction Box Material Selection

Junction Box Selection Considerations

When choosing junction boxes, it is essential to prioritize the correct size and adequate protection. The material type and professional rating systems should also be considered when considering protection quality. Additional features such as inner boards and battery cases can also be important depending on the application.

Materials Types of Junction Boxes

It is important to note that you will require a junction box for your electrical connection. However, the material you choose for your junction box can significantly affect its performance and durability. Different materials have unique characteristics that make them suitable for specific applications. You will commonly come across plastic, metal, and fiberglass as some of the materials you can choose from.


Metal is suitable for a junction box due to its strength and durability in extreme environments. Aluminum, steel, and stainless steel are the most commonly used metals for making junction boxes, each having unique properties suitable for specific purposes.

Aluminum is an excellent conductor of electricity, making it ideal for electrical applications. Steel junction boxes, on the other hand, are recognized for their sturdiness and durability, making them an excellent choice for industrial and commercial settings where extreme conditions and harsh environments require the highest level of protection. 

Stainless steel is also a viable option for making junction boxes, as it is highly durable, corrosion-resistant, and strong. Its non-magnetic properties benefit it in applications where magnetic interference could be problematic. Additionally, stainless steel can withstand harsh environmental conditions, making it ideal for outdoor environments.

Advantages of Metal Junction Boxes

  • Fire resistance: Metal junction boxes resist fire and prevent spreading.
  • Durability: Metal junction boxes are durable and ideal for harsh environments.
  • EMI/RFI shielding: Steel and aluminum can shield electronics from EMI and RFI.

Disadvantages of Metal Junction Boxes

  • Corrosion: Some metals are corrosion-resistant, but exposure to moisture and other corrosive factors can weaken the junction box and reduce its lifespan.
  • Cost: Metal junction boxes cost more than plastic ones due to materials and manufacturing.
  • Weight: Metal junction boxes cost more than plastic ones due to materials and manufacturing.
  • Conductivity: Improper grounding of metal conductivity can be dangerous.


Plastic junction boxes are affordable and convenient. ABS, PVC, and polycarbonate are commonly used in their construction. ABS is known for its excellent impact resistance and ability to withstand extreme temperatures. PVC is strong and resistant to impact, chemicals, and high temperatures. Polycarbonate is flame—and UV-resistant. 

Advantages of Plastic Junction Boxes

  • Easy To Install: Plastic electrical boxes are easy to install, particularly in new construction where studs and joists are exposed. They come with nails already fastened, making the process quick and easy.
  • Non-conductive: Plastic boxes are safer for handling and installation than metal ones, as they don’t conduct electricity.
  • Lightweight:  Choose plastic boxes over metal for easy handling and movement.
  • Cost Saving: Plastic boxes are more affordable than metal boxes, making them economical for many applications.
  • Built-in cable clamps: It helps secure your electrical cable, saving you money and time.

Disadvantages of Plastic Junction Boxes

  • Grounding: For electrical systems that require a ground connection to be safe, avoid plastic boxes, as they can break the connection and create a hazard. Use metal junction boxes instead.
  • Durability: Metal boxes are more durable than plastic ones. Plastic brackets and screw holes break easily, making it challenging to attach devices securely.


Fiberglass and polycarbonate are equally competitive. Fiberglass is a great insulator, tough, and affordable, but it costs more than polycarbonate, which is more suitable for residential applications.

Advantages of Fiberglass Junction Boxes

  • Lightweight: Fiberglass boxes are lighter and easier to install than metal boxes.
  • Corrosion resistance: Fiberglass is resistant to corrosion, making it ideal for use in environments where the junction box may be exposed to salt water or chemicals.
  • UV resistance: Use fiberglass for outdoor junction boxes due to its excellent UV resistance.
  • Design flexibility: Fiberglass is highly moldable, allowing customized designs to meet specific needs.

Disadvantages of Fiberglass Junction Boxes

  • Challenging to install: Fiberglass junction boxes may be more challenging to install than metal or plastic ones, as special tools and techniques such as drilling or cutting may be required.
  • Limited temperature scope: Fiberglass is not recommended for high or low-temperature applications, as it can cause the junction box to warp or crack.
  • Vulnerability to impact damage: Fiberglass boxes are less impact-resistant than metal ones, which can be risky if the box is bumped or struck.

Junction Box

Understanding Material Ratings

It’s important to know that junction boxes are all different. They have different ratings based on their performance characteristics, established by industry standards like NEMA, UL, and IP ratings. Understanding these ratings is crucial to choosing the correct junction box for your needs.

NEMA Ratings

The National Electrical Manufacturers Association is a professional trade organization that develops electrical equipment and systems standards. It uses NEMA ratings to describe how well enclosures protect against various environmental factors. Junction boxes can have NEMA ratings ranging from 1 to 13, with higher numbers indicating greater protection against water, dust, corrosion, and other environmental factors.

UL Ratings

UL is short for Underwriters Laboratories, an independent company dedicated to testing and certifying products for safety and performance. Regarding junction boxes, UL ratings are given based on factors such as flame resistance, impact resistance, and electrical safety. The two most common UL ratings for junction boxes are UL 50 and UL 94. UL 50 indicates the enclosure’s ability to protect against water, dust, and other solid objects. On the other hand, UL 94 measures the enclosure’s flame resistance.

NEMA TypeDescription
1These boxes are designed for indoor use to protect personnel from contact with internal components and from falling dirt.
2Designed for indoor use to protect against dirt and limited amounts of falling water.
3IP-rated junction boxes are suitable for outdoor and indoor use to protect against sleet, rain, windblown dust, and external ice formation.
3RThese junction boxes can be used indoors and outdoors, protecting against falling sleet, rain, and external ice formation.
3SThese junction boxes, suitable for outdoor and indoor use, protect against rain, sleet, windblown dust, and external ice formation.
3X, 3RX, 3SX“X” is a symbol that indicates extra corrosion protection, typically applied in areas near salt water.
4Designed for outdoor and indoor use to protect against hose-directed or splashing water, windblown dust, rain, and external ice formation.
4XSuitable for outdoor and indoor use, these junction boxes provide protection against windblown dust, rain, hose-directed and splashing water, and external ice formation.
5Dust-tight enclosures are equipped with gaskets or equivalent to prevent dust from entering, and are commonly used in steel mills and cement plants.
6Designed for outdoor and indoor use to protect against limited depth temporary submersion and external ice formation.
 6PSuitable for outdoor and indoor use to protect against prolonged immersion in relatively shallow depths and external ice formation.
7 Certified and labeled for indoor use in areas with hazardous conditions classified as Class I, Groups A, B, C, D as per the NFPA standards including the NEC.
8Certified for indoor and outdoor use in Class I, Groups A, B, C, D locations as defined by NFPA standards, such as NFPA 70.
9Certified and labeled for both indoor and outdoor use in locations categorized as Class II, Groups E, F, or G as per the NFPA standards, including the NEC.
10Meets the conditions of the Mine Safety and Health Administration, 30 CFR Part 18 (1978) for safety in mining operations.
11Designed for outdoor use to protect enclosed gadgets against corrosive gases and liquids, by oil submersion.
12Designed for indoor use to protect against falling dirt, dust, and dripping non-corrosive liquids.
12KDesigned to protect against dripping non-corrosive liquids, falling dirt, and dust.
13Distinct junction boxes are designed for indoor use to protect against spraying water, dust, non-corrosive coolants, and oil.

IP Ratings

IP stands for Ingress Protection, a system used to rate how well an enclosure can protect against the entry of solid objects and liquids. The IP rating consists of two numbers. The first indicates the protection level against solid objects, and the second indicates the protection level against liquids. For instance, an IP65-rated junction box can shield against dust and water jets.

When choosing a junction box, it is essential to consider the application’s specific needs and opt for a box with the appropriate rating. For example, junction boxes utilized in outdoor settings may call for a higher NEMA rating to safeguard against water and weathering. On the other hand, those used in hazardous locations may require a particular UL rating for electrical safety. By carefully considering the material rating, one can ensure that the junction box will provide the necessary protection and performance for the intended application.

Steps for Choosing the Right Material

Choosing the right material for your junction box is crucial as it can impact its performance, durability, and safety. Follow these steps to select the best material for your junction box:

Specify the application

Consider the size of the enclosure, the number and type of electrical junction boxes, and the level of protection needed.

Set the installation location

Know where the junction box will be installed, such as indoors or outdoors. Consider whether it will be exposed to moisture, chemicals, or other environmental factors.

Evaluate environmental factors

Environmental factors like temperature, humidity, and corrosive substances can impact the performance and durability of a junction box. Consider these factors when selecting a material.

For instance, if you expose the junction box to harsh chemicals, materials like fiberglass or stainless steel may be better than plastic.

Comprehend material ratings

Different materials, such as NEMA and IP ratings, indicate their protection level against environmental factors. Understanding these ratings can help you select the suitable material for your junction box.

Consider budget

Finally, consider your budget when selecting a material for your junction box. Remember to consider the material’s long-term cost, including its durability, maintenance requirements, and initial cost.


Is it safe to use plastic electrical boxes for outdoor installations?

Plastic junction boxes can be more cost-effective for outdoor applications than metal ones. Heavy-duty plastics, like polycarbonate, can perform better than metal.

How to make a waterproof junction box?

At Enze, we use rubber seals and gaskets to create a watertight barrier in your stainless steel junction box that protects against water, dust, chemicals, and ice.


If you have any questions or need assistance choosing the right material for your junction box, our team is always ready to help you. Contact us for the perfect electrical solution.