Precision Engineering for Global OEMs

Custom Junction Box services

From rapid prototyping to high-volume production, Supro MFG delivers one-stop precision metal fabrication with ISO-certified quality. Reduce your lead times and production costs with our expert DFM support.

1-3 day Rapid Prototyping & Agile Supply Chain Delivery.
On-time delivery of high quality product commitments.
Extensive Material Selection & Industrial-Grade Finishing.
Direct-from-Factory Pricing & Transparent Costing.
ISO 9001-2015 / IATF 16949:2016 certified system.
Integrated Assembly: Delivering finished, ready-to-use products, not just components.

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Rapid Prototypes, DFM Optimization, On-Time Delivery, Real Manufacturer Quote.

Rapid stamping die Turnaround

Committed to exceeding expectations for quality and rapid turnaround, and meeting high-quality sheet metal parts.

Consistency & high quality

Whether it is rapid prototyping & large-volume manufacturing, we will implement it according to customer needs and standards.

Low Cost Effective

Integrate product design, bending, stamping, cutting, surface treatment, etc. to provide a series of manufacturing solutions.

Precision Metal Fabrication Services in China | Custom OEM Solutions & Rapid Prototyping

Your Strategic Partner for Junction Box Fabrication

At Supro MFG (Supro Manufacturing Co., Ltd.), we don’t just manufacture parts; we engineer reliability. As a leading China metal fabrication factory, we bridge the gap between complex design and cost-effective production. By leveraging our ISO 9001:2015 & IATF 16949 certified facilities and a seasoned engineering team, we provide 3,000+ global clients with unparalleled custom metal fabrication services—direct from the source with transparent, manufacturer-level pricing.

We specialize in the high-quality manufacturing and assembly of custom metal parts, with processing capabilities encompassing: sheet metal fabrication, metal stamping, CNC machining, laser cutting, metal welding, metal spinning, deep drawing, aluminum extrusion, die casting, as well as customized finished product assembly and surface treatment services.

From concept prototypes to mass production,

Supro MFG is your most reliable partner and you will benefit from our manufacturing services.

What Is a Junction Box?

A junction box is a critical sheet metal enclosure designed to safely house and organize electrical connections. It is intended to protect complex wiring connections from harmful environmental factors and mechanical impact, while preventing accidental electric shock and fire.

To ensure strict compliance with NEMA and IP protection rating standards, professionally manufactured junction boxes must possess absolute structural integrity. We manufacture these specialized enclosures using high-quality 14- to 16-gauge stainless steel or galvanized steel. By employing high-precision CNC laser cutting and precision bending processes, combined with continuous TIG/MIG seam welding and industrial-grade powder coating, we ensure our products offer exceptional resistance to moisture, dust, and corrosion.

At Supro MFG, leveraging our deep expertise in custom sheet metal fabrication, we provide one-stop junction box solutions—featuring precision punching, custom mounting brackets, and exact dimensions—that integrate seamlessly into your electrical infrastructure.

Custom Junction Box fabrication Material Solutions

At Supro MFG, we offer a full range of metal materials to meet the demanding requirements of any industry or environment, and we can proactively advise our customers on metal fabrication techniques that utilize the properties of the materials to maximize the life and functionality of their products.

Galvanized Steel

Offers high structural strength and excellent fire resistance. This type of junction box is highly resistant to mechanical impact and is widely used for indoor wiring and exposed wiring installations in commercial buildings.

Die-Cast Aluminum

Lightweight with inherent EMI shielding and corrosion resistance. Widely used in power distribution junction boxes for industrial automation and heavy-duty outdoor machinery.

304/316 Stainless Steel

Extremely resistant to acids and alkalis, corrosion-resistant, and capable of withstanding high-temperature cleaning. These junction boxes are specifically designed for food processing, marine engineering, and highly corrosive chemical environments.

Polycarbonate (PC)

Offers excellent impact resistance and outstanding UV resistance. Junction boxes made from this engineering plastic are commonly used in solar photovoltaic systems and for electrical wiring in harsh outdoor environments.

Fiberglass (GRP)

Highly insulating, rust-free, and resistant to severe chemical corrosion. Junction boxes made from this material have an extremely long service life and are ideally suited for wastewater treatment plants and environments with high humidity and salt spray.

ABS Resin

Cost-effective, easy to machine and drill, and shock-resistant. Primarily used for standard indoor electronic equipment enclosures or residential junction boxes with protective covers.

Securing Your Designs with Enterprise-Grade Confidentiality at Every Stage of Manufacturing

Your Innovation, Protected:
Uncompromising IP Security & NDA Compliance

At Supro MFG, we understand that your designs are your most valuable assets. As a strategic sheet metal stamping partner, our commitment to your intellectual property is absolute. We operate under a strict Zero-Leak Policy, ensuring that every blueprint, CAD file, and prototype remains strictly confidential within our secure engineering ecosystem.

We proactively offer comprehensive Non-Disclosure Agreements (NDAs) that align with international legal standards, providing you with a transparent and enforceable framework for cooperation. Beyond legal paperwork, our internal protocols include segmented data access, secure server encryption, and rigorous staff training on IP sensitivity. Whether you are a startup scaling a disruptive product or an OEM managing sensitive aerospace components, Supro MFG acts as a secure extension of your own facility. Partner with a metal stamping manufacturer that values your competitive advantage as much as you do.

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Common Issues with Junction Boxes

When sourcing custom junction boxes for commercial or industrial electrical infrastructure, structural integrity is just as important as electrical safety. Substandard sheet metal fabrication can lead to reduced NEMA/IP ratings, difficult on-site installation, and premature product failure. Below is an analysis of the most common defects found in junction boxes, including their root causes and the rigorous manufacturing solutions we implement to prevent them.

Incomplete Corner Welding, Leading to Failure of IP/NEMA Ratings

Minor gaps at the flanges of junction boxes allow water and particulate matter to penetrate, resulting in failure to pass NEMA 4/4X or IP66 testing. The root cause is reliance on intermittent spot welding or inconsistent manual welding speeds, rather than sealing the entire corner joint.

We employ an automated robotic TIG/MIG continuous seam welding process. Each external corner is fully welded, ground smooth, and subjected to rigorous penetrant leak testing to ensure an absolute environmental seal.

Misalignment of Internal Mounting Studs

The junction box’s internal backplate or DIN rail fails to align with the pre-installed mounting studs, preventing on-site wiring. The root cause is: cumulative tolerances during the CNC bending process, or welding distortion causing the internal mounting studs to shift out of position.

We employ active angle measurement technology on our CNC bending machines to eliminate bending errors. Internal hardware is installed using precision welding fixtures and an automatic hardware insertion press, ensuring micron-level positional accuracy.

Peeling of Powder Coating on Junction Box Edges

The powder coating on the bends and edges of the junction box is prone to peeling, exposing the base material and causing rapid oxidation. The root cause is improper surface preparation (residual stamping oil) or the “Faraday cage” effect, where the powder cannot adhere to sharp, unchamfered edges.

All Supro parts undergo automatic chamfering followed by a rigorous five-stage phosphating and cleaning process. We regularly verify coating adhesion using the ASTM D3359 cross-tape test method.

Box Corner Deformation Caused by Pallet Drops

Upon arrival, the Junction Box’s corners were crushed, preventing the cover plate from being installed and compromising the enclosure’s integrity. The root causes are: overloading of standard corrugated cartons, or failure to reinforce the corners of shipping pallets carrying heavy metal products.

Supro packs the junction boxes in double-walled export cartons and reinforces the corners with high-density foam padding. Pallets are equipped with rigid V-shaped corner protectors and heavy-duty PET strapping to ensure the products can withstand the rigorous loading and unloading operations during global shipping.

No design files? Let Supro MFG do it for you.

We often come across clients who have no professional design drawings and documentation, only a creative idea, which leads to the project being at a standstill.

If you are in this situation, then contact our team of experts.

Supro MFG, as an industry-leading custom metal fabricator, has an ever-experienced team of engineers who utilize their extensive fabrication experience and technical expertise to build your idea into a real product and create design files such as STEP/STP/SLDPRT/DXF/PDF/PRT/DWG/AI.

That’s what makes SUPRO MFG so great, and 2,000 corporate, entrepreneurial, artist, and other purchasers from around the world enjoy working with us and benefiting from our one-stop manufacturing services.

One-Stop Solution for Custom Junction Box

Typical Applications for Junction Box

Solar & PV Systems

These systems are exposed to intense UV radiation and extreme temperature fluctuations year-round. Junction boxes are typically required to have an IP67/IP68 waterproof rating, be made of materials that pass the UL 746C UV resistance test, and be equipped with diodes to prevent reverse current flow.

Industrial Automation and Mechanical Control

Workshop environments are often dusty and oily, with a risk of mechanical impact. This scenario requires junction boxes to have a high IK impact resistance rating, and the sealing strips must be oil-resistant and age-resistant to ensure that PLCs or I/O modules remain free from contamination.

Commercial & Residential Wiring

Whether installed in-wall or surface-mounted, electrical distribution systems in these settings have extremely high fire safety and compliance requirements. Junction boxes for these applications must strictly comply with UL 514A/B or CE standards, provide good ground continuity, and are typically made of galvanized steel with punch-through holes.

Marine & Offshore Applications

These environments face high salt fog corrosion and intense wave impact. Junction boxes in this sector are required to meet NEMA 4X or IP66 protection ratings or higher, with materials limited to 316 stainless steel or GRP, to strictly prevent moisture ingress that could cause short circuits.

Hazardous and Explosion-Proof Locations

These environments contain flammable gases or dust (e.g., in the petrochemical and mining industries). Junction boxes must be certified to ATEX/IECEx explosion-proof standards. The enclosures are typically made of thick-walled die-cast aluminum or heavy-duty steel, capable of withstanding internal explosions without igniting the external environment.

Outdoor Security & Infrastructure

Nodes are dispersed, exposed to the elements, and at risk of theft. Junction boxes must feature both lightweight construction and vandal-resistant design; they are typically made of IP65-rated PC or aluminum to ensure all-weather transmission of fiber optics and power.

A part is only as good as its finish.

High-Performance Surface Finishing: Aesthetics Meets Durability

At Supro MFG, we understand that professional custom metal fabrication requires more than just structural integrity—it demands surface treatments that withstand harsh environments and strict aesthetic standards.

Our integrated finishing shop provides a seamless transition from the production line to the final coating, ensuring tight control over lead times and quality.