O-Pin vs U-Pin in Solar Connectors: Why Tier-1 Brands (Trina, LONGi) Prefer O-Pin

Tier-1 solar brands don’t make decisions lightly. The pin shape inside a solar connector may seem small, but it makes a big difference in reliability and performance. So, which do they trust more—O-pin or U-pin?

Most Tier-1 solar panel manufacturers now prefer O-pins in their MC4 connectors due to better durability, conductivity, and long-term field performance.

Let me explain why the big brands are shifting. We’ll look at how O-pins compare with U-pins in the real world—and why this choice matters in high-value solar projects.

Which Pin Type—O or U—Do Brands Like Trina and LONGi Use by Default?

Trina and LONGi, two of the world’s leading Tier-1 solar panel brands, have transitioned toward connectors compatible with machined O-pins¹. Trina, for example, moved to TS4 connectors², which allow better contact performance. Many of these connectors are Staubli-compatible³ and feature solid machined contacts—O-shaped.

Why this matters: This isn’t just a branding change. It reflects real operational priorities. These manufacturers are under pressure to deliver long-term field reliability, meet international safety standards, and reduce warranty claims.

Dive deeper: What’s behind this shift?

Brand	Connector Standard	Default Pin Type	Notable Change
Trina Solar	TS4 (Staubli-compatible)	O-pin	Shifted from MC4/UTX
LONGi Solar	MC4-Evo 2 / TS4	O-pin	Focus on TÜV + heat

Both companies emphasize low resistance, longer life, and stronger mechanical bonding. O-pins help them meet these targets better than stamped U-pins.

Why Do Most Tier-1 Manufacturers Favor O-Pin Over U-Pin in MC4 Connectors?

It comes down to performance. O-pins are machined from solid metal. U-pins are stamped and bent from thin metal sheets. This simple manufacturing difference leads to major field outcomes.

O-pins are stronger, more stable, and deliver lower contact resistance over time.⁴

Here’s what manufacturers like Trina, LONGi, and JinkoSolar are prioritizing:

• Stronger mechanical grip⁵: O-pins hold contact tension longer. This means fewer thermal disconnects.
• Lower electrical resistance⁶: More contact points = less heat = more stable current.
• Better corrosion resistance: O-pins have less exposed surface area for moisture or salt to attack.
• Fewer connector recalls or warranty claims: Less risk = lower cost.

In a 25-year installation, these small differences matter a lot.

Are U-Pin Contacts More Prone to Field Failures in Utility-Scale Solar?

Yes. U-pin contacts⁷—being stamped and thinner—are more likely to deform under high current or heat. I’ve seen it in practice. When installers crimp U-pins improperly, the risks skyrocket.

Deformed or loose U-pins can cause hot spots, voltage drops, and even fire hazards⁸.

Here’s what goes wrong in real-world conditions:

• Vibration loosens weak crimps
• Thermal expansion breaks weak contact tension
• High current heats up the small contact area
• Moisture sneaks into gaps and causes corrosion

Let’s compare:

Failure Mode	U-Pin Risk	O-Pin Risk
Crimp loosening	High	Low
Heat build-up	Medium	Low
Corrosion in contact area	High	Low
Mechanical deformation	High	Low
Fire due to arc formation	Medium	Very Low

That’s why many EPCs and project developers now specify O-pin-compatible connectors for utility-scale plants.

How Does O-Pin Design Lower Maintenance Costs for Large-Scale PV Systems?

O-pins help lower both short-term troubleshooting and long-term maintenance budgets.

With fewer connection failures, O-pins reduce inspection frequency⁹ and repair events.

Here’s how this plays out in cost:

• Lower downtime: Fewer loose connectors or hot spots = more uptime.
• Lower labor cost: Less connector replacement or re-crimping.
• Longer intervals between checks: More confidence in long-term stability.
• Less thermal degradation: O-pins resist aging in desert or coastal weather.

In large systems where thousands of connectors are used, even a 1% failure rate can lead to huge service costs. O-pins keep those numbers down.

Conclusion

Most Tier-1 manufacturers like Trina and LONGi now prefer O-pins in their MC4 connectors. O-pins offer stronger contact force, better heat resistance, and more reliable long-term performance—especially in harsh environments or utility-scale setups.