Why Does Stäubli Offer Both U-Type and O-Type Terminals for Their MC4 Connectors?

Many solar installers struggle to understand why Stäubli offers two types of MC4 terminals. One is open-ended, the other is closed—but both serve different installation needs.

Stäubli offers both U-type and O-type MC4 terminals to meet different requirements in field installations and automated production lines.

If you're confused about which pin design to choose, don’t worry. I’ve broken it down based on safety, compatibility, and real-world use.

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What’s the Functional Difference Between U-Type and O-Type MC4 Terminals?

Choosing the wrong terminal shape could lead to loose connections or even failed certification tests.

U-type MC4 terminals¹ are crimped manually on-site, while O-type terminals² are pre-crimped and used in automated production.

Dive Deeper: U vs O Explained

Feature	U-Type Terminal	O-Type Terminal
Shape	U-shaped (open barrel)	O-shaped (closed barrel)
Crimping Method	Manual, on-site	Automated, factory crimped
Installation Use	Field-installations	OEM/pre-assembled strings
Risk of Error	Higher, if tools are poor	Lower, factory-controlled
Repair Flexibility	High (can redo crimp)	Low (usually sealed units)

I usually recommend U-type for projects where custom cable lengths are needed or in retrofit jobs. O-type is ideal for mass production lines where every string is identical and speed is critical.

Why Does Multilam Contact Technology Support Both Pin Designs?

You might wonder why Stäubli doesn’t just pick one terminal shape and stick with it.

Because their MULTILAM contact system³ is flexible, it can maintain low resistance in both U-type and O-type terminals⁴.

Dive Deeper: MULTILAM Works for Both

MULTILAM is the tiny contact strip inside the MC4 that maintains spring pressure on the terminal pin. It adjusts itself to ensure:

• Reliable connection under vibration
• Resistance to corrosion and thermal cycling
• Over 25 years of field operation

Whether the pin is U-type or O-type, MULTILAM keeps the connection tight. It adapts to slight differences in shape without losing contact pressure.

That’s how Stäubli can offer both designs without sacrificing performance or safety.

Which Pin Type Performs Better in High-Current or High-Temperature PV Installations?

When the current rises, so does the heat. And that can change everything.

O-type terminals are more stable under high-current and high-temperature loads⁵, thanks to their solid cylindrical contact area.

Dive Deeper: Performance Under Pressure

In environments where ambient temperatures hit 60°C and current exceeds 30A:

• O-type terminals perform better because they have more uniform surface contact.
• U-type terminals are still safe, but depend more on perfect crimping.

Stäubli’s lab tests show lower contact resistance⁶ and less micro-arcing in O-type terminals over 10,000 cycles of thermal stress.

If you’re building solar arrays in deserts, industrial rooftops, or floating platforms—go with O-type.

Are U-Type or O-Type Pins More Common in Tier-1 Solar Projects?

Tier-1 solar projects rarely compromise on speed, consistency, or certification.

Most Tier-1 solar projects use O-type terminals because they come pre-crimped and meet factory-level quality standards⁷.

Dive Deeper: Why Tier-1 Favors O-Type

In my experience working with EPCs in Australia and Southeast Asia, procurement teams prefer O-type for these reasons:

• Fewer variables: Everything is factory-tested.
• Speed: No time wasted on crimping in the field.
• Compliance: Easier to meet TÜV and UL audit trails⁸.

However, U-type still has a place—especially in distributed or residential solar, where field teams cut cables to fit roof shapes or retrofitted carports.

How Do Stäubli’s Dual Pin Options Improve Installation Flexibility and Safety?

Here’s the smart part—Stäubli doesn’t lock you into one system. They give you options.

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Dive Deeper: Why Dual Options Make Sense

• Installer Flexibility⁹: Field technicians can adapt to any site condition using U-type.
• Manufacturing Efficiency¹⁰: OEMs automate crimping and avoid human error with O-type.
• Global Compliance: Both terminal types pass TÜV/UL when used correctly.

More importantly, if a connector is properly installed—U or O type—it still benefits from MULTILAM technology¹¹ and retains a 25-year rated lifespan.

Stäubli is playing the long game here: offering compatibility, safety, and ease of use to both ends of the solar industry.

Conclusion

Stäubli offers both U-type and O-type MC4 terminals because real-world solar projects need both flexibility and factory-grade precision.