🔩 Do you know American standard metal junction boxes?

ELECTRICAL KNOWLEDGE

1.Don’t know the specific UL standards for metal junction boxes?

2.Can’t tell the difference between hot-dip galvanizing and electro-galvanizing?

3Unsure which junction box material fits which scenario?

Let Linsky break it down for you today—let’s dive in and learn together!

01

Standards First: Compliance Foundations of American Standard Metal Boxes

The core processes of American standard metal junction boxes must strictly adhere to three key specifications: National Electrical Code (NEC), UL standards (e.g., UL 514B, UL 1203), and NEMA standards. All process designs must meet core requirements such as fire resistance, explosion protection, and corrosion resistance, ensuring products comply with electrical safety standards in North America and global markets from the source.

02

Forming Processes: From Raw Materials to Housing

🔨 Casting Processes (for housings)

1.Die Casting

• Applicable material: Aluminum alloy
• American standard requirements: Must meet UL 50E protection ratings; casting wall thickness ≥1.6mm (UL 514B)
• Process: Mold preheating → High-pressure injection → Rapid cooling → Deburring → X-ray inspection for pores (ASTM E505)

2.Sand Casting

• Applicable materials: Cast iron, cast steel

• American standard requirements: Gray cast iron tensile strength ≥20ksi; explosion-proof scenarios require passing UL 1203 explosion pressure test

• Advantage: Suitable for heavy industrial scenarios, with better impact resistance than die casting

⚙️ Stamping Processes (Thin-walled components)

• Applicable materials: Galvanized steel, stainless steel
• Key processes:
  Blanking and punching (precision ±0.1mm, compliant with NEMA 250 waterproof groove design)
  Bending and forming (bend radius ≥2×sheet thickness to avoid stress concentration)

Metal Box

03

Precision Machining: Refinement from Rough Blank to Finished Product

🔥 Welding Processes (Key to Structural Splicing)

01

TIG Welding

• Application scenario: Stainless steel housing splicing

• Quality requirement: Welds must pass ASTM A262 corrosion test to ensure no pores; alternatively, cracks

02

Laser Welding (High-Precision Joining)

• Core advantage: Small heat-affected zone, suitable for explosion-proof surface splicing

• American standard requirement: Explosion-proof surface roughness Ra ≤3.2μm (mandated by UL 1203 explosion-proof certification)

🛠️ Machining Processes (Detail Refinement)

01

CNC Precision Machining

• Machining content: Sealing surfaces, flameproof surfaces, cable entry threads (NPT or Metric)

• Precision requirements: Flatness of flameproof surfaces ≤0.05mm (UL 1203); threaded holes comply with ASME B1.1

02

Tapping and Deburring

• Key requirement: Ground terminal threads must pass UL 514B torque test (e.g., M6 bolt torque ≥5 N·m) to ensure reliable grounding

# PRODUCT

04

Protective Treatment: Dual Protection of Weather Resistance and Safety

🛡️ Surface Treatment (Core of Corrosion Resistance)

01

Anti-Corrosion Treatment

• Galvanized steel: Hot-dip galvanizing (ASTM A123), coating thickness ≥85μm, passing 500-hour salt spray test (ASTM B117)

• Aluminum alloy: Anodizing (MIL-A-8625 Type II/III), film thickness ≥10μm to enhance weather resistance

• Stainless steel: Pickling and passivation (ASTM A967) to remove weld oxide layers and strengthen rust resistance

02

Spraying/Coating (Durability and Identification)

• Epoxy resin spraying: Thickness ≥60μm (ASTM D7091), passing NEMA 4X 1000-hour UV aging test

• Color specification: RAL 7035 (light gray) commonly used outdoors, meeting UL 50 color fastness requirements

🧩 Sealing and Insulation (Safety Guarantee)

01

Sealing Treatment

• Sealing rings: EPDM rubber (UL 50E certified), temperature resistance -40℃~120℃, compression set ≤30%

• Potting compound: Epoxy resin potting (UL 94 V-0) for internal electrical isolation in explosion-proof boxes

02

Insulation Treatment

• Internal partitions: Polycarbonate (PC) ; alternatively, nylon (PA66), UL 746A arc resistance ≥180 seconds

• Grounding design: Contact resistance between ground terminal and housing ≤0.1Ω (NEC Article 250.96)

05

Quality Inspection: Final Line of Compliance Before Delivery

📏 Key Testing Items

• Sealing test:
  Pressure test (0.2MPa for 5 minutes, leakage ≤0.1 L/min, UL 50E)
  Immersion test (1m water depth for 30 minutes without leakage, NEMA 6P)
• Electrical safety test:
  Insulation withstand voltage (2500V for 1 minute without breakdown, UL 514B)
  Ground continuity (ground resistance ≤0.1Ω, NEC Article 250)
• Explosion-proof test (UL 1203):
  No housing deformation under 1.5×maximum explosion pressure; flameproof surface gap ≤0.15m (Class I, Division 1)

💡 Core Process Summary

The essence of American standard metal junction box processes lies in "compliance" and "reliability":

• Materials must pass UL yellow card and ASTM certification;

• Explosion-proof surface precision (Ra ≤3.2μm) and surface corrosion resistance (salt spray ≥500 hours) are key control points;

• Sealing (IP67) and electrical testing (2500V withstand voltage) are safety baselines.

06

Conclusion: Processes as the Foundation, Safety as the Core

Every process, from casting to testing, carries a commitment to safety. Linsky’s American standard metal junction boxes strictly adhere to UL/NEC standards, using precision processes to safeguard electrical safety, suitable for industrial, outdoor, and other scenarios.

Want to learn more about American standard electrical products? Follow Linsky Electrical’s official account ; alternatively, contact us via:

📞 Contact Us: 

• Website: www.shlinsky.com

• Email: sales@linsky.cn

• Phone: +86-21-67107908

• Shanghai Headquarters: Room 1002, Building 2, Fengchuang Valley, No. 1588 Huhang Highway, Fengxian District, Shanghai, China

• Shanghai Factory: Workshop 2, No. 29, Lane 1888, Daye Highway, Fengxian District, Shanghai, China

• Cambodia Factory:SantepheapVillage，Taing Krouch Commune， Samrong Torng District，Kampong Speu Province，Cambodia

Let professional processes safeguard your electrical systems!

END

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Editor-in-Chief: USLinsky   

Current Editor: Suzlyn Ou   

Current Copywriter: Suzlyn Ou

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