How SWM3Z DC MCCB Reduced Downtime by 47% in Solar Plants

A regional renewable energy operator managing 12 solar PV plants across the southwestern United States was losing revenue to repeated breaker trips and arc failures on its DC distribution boards. After switching to the SINGI SWM3Z DC MCCB, the company cut unscheduled downtime by 47% and reduced annual maintenance costs by $52,000. This case study details the challenges, the decision process, and the measurable outcomes.

What Was the Customer Background?

The operator runs 320 MW of PV capacity across Arizona, Nevada, and California, serving wholesale markets and corporate power purchase agreements. The fleet includes fixed-tilt and single-axis tracking installations, with array volt-levels up to 1000 VDC. Maintenance teams handle preventive and corrective work from three regional depots. The company also operates a 40 MW battery energy storage system, which shares the same DC protection architecture.

What Challenges Led to the Switch?

In early 2023, the operator noticed an uptick in DC breaker trips during high-irradiance periods. Many of the existing breakers were specified for AC circuits and retrofitted into DC combiner boxes. At 800–1000 VDC, their arc extinction capability was inadequate, leading to contact erosion and, in three cases, internal arc-flash incidents. Each unscheduled outage cost an average of $6,500 in lost generation and dispatch delays. Fuses were tested as an alternative, but they required frequent replacement and could not handle the inrush currents from inverter capacitors. Maintenance crews spent up to 18 hours per month troubleshooting intermittent trips at remote sites, with no definitive root cause.

Why Did They Choose the SWM3Z DC MCCB?

The operator assessed three options: replacing with another AC MCCB, adding fuse blocks, or switching to a purpose-built DC MCCB. The first was rejected because AC breakers still lack the DC interruption rating needed for photovoltaic circuits. Fuses were rejected because of non-resettable operation and the logistics of carrying multiple fuse sizes in inventory. The SINGI SWM3Z DC MCCB was chosen because it uses a magnetic blow-out system that extinguishes DC arcs, offers a thermal-magnetic trip mechanism that can be tuned for chooseive coordination, and is listed under UL 489, the standard for molded-case circuit breakers. That UL 489 listing allowed the operator to maintain insurance coverage and comply with NEC requirements without custom engineering.

How Was the SWM3Z DC MCCB Implemented?

The rollout spanned nine weeks and followed a structured approach:

• A full audit of all combiner boxes and DC switchboards to map volt-level, current, and fault-amperage conditions at each site.
• A pilot installation on two plants with the highest trip rates to validate the product under real operating conditions.
• A teardown inspection after four weeks of service to confirm that the contacts showed no wear or carbon tracking.
• A phased rollout to the remaining ten plants, replacing 148 breakers in total.
• Reconfiguration of trip curves to match the DC input characteristics of each inverter model.
• Training for field crews on torque settings, terminal inspection, and arc-flash boundaries.

The main difficulty was that the original combiner box busbars were spaced for the older breakers' terminals. The SWM3Z's compact footprint left a gap on the mounting plate, and the team had to maintain correct insulation distances. This was resolved by having a local fabrication shop produce laser-cut insulated spacer plates. The retrofit process took 45 minutes per breaker, and no live busbar modifications were required.

What Quantitative Results Were Achieved?

Twelve months after the rollout, the operator measured the following results:

• Unscheduled downtime fell from 9.4 hours per month to 5.0 hours per month, a 47% reduction.
• DC breaker failures across the fleet dropped from 11 incidents in the preceding twelve months to 3 incidents in the twelve months after the switch, a 73% reduction.
• Maintenance labor and replacement parts costs decreased by $52,000 per year, including fewer truck rolls and no fuse replacements.
• The upgrade paid back in 14 months.

No arc-flash incidents have been reported since the deployment. The operator has also standardized on the SWM3Z for a new 50 MW expansion and for retrofits at a co-located battery storage project.

What Does the Customer Say?

“The SWM3Z DC MCCB eliminated the intermittent trips we were chasing for months. Our field crews trust it, and the absence of arc damage is obvious when we open the cabinets during inspections.”

— Director of Operations, renewable energy asset operator

What Lessons Can Other Facilities Learn?

• Never substitute AC breakers for DC circuits. DC arcs require active blow-out within the interruption chamber, and a product without DC ratings will wear out and fail unpredictably.
• Match trip curve settings to the actual load and source characteristics, not the cable ampacity. Inverter inrush amperage and PV module short-circuit amperage both affect breaker performance.
• Run a small pilot before a fleetwide rollout. Inspect the breaker internals after a few weeks of operation to catch any installation compatibility issues before scaling.
• If the original busbar spacing is incompatible, use adjustable mounting kits or laser-cut insulated spacers instead of drilling new holes in live panels. That reduces downtime and keeps the panel energized during retrofits.

Industry Standards References

• UL 489 Ed. 14-2025 — Molded-Case Circuit Breakers, Molded-Case Switches and Circuit-Breaker Enclosures
• UL 1699B:2018 — Photovoltaic (PV) DC Arc-Fault Circuit Protection