Procurement Guide for DC & PV Circuit Breakers

1. Why DC needs a different breaker

An AC arc quenches at the current zero of the sine wave; a DC fault has no such zero, so the breaker must force interruption against a rising recovery voltage. That is why a generic AC MCB will not reliably clear a PV fault.

Polarity matters. Reverse the string and the same device may fail to open on the return path. DC-rated units are built and tested for this.

2. Voltage staging and string layout

For a 1000 V DC battery system the device must hold off the full bus and clear a bolted fault within the let-through energy the downstream cable can survive.

• Stage the voltage — size the breaker to the maximum string open-circuit voltage, not the operating voltage.
• Polarity aware — confirm the marking matches the PV + and - bus in the combiner.
• PV string protection — one device per string, coordinated with the inverter input fuse.

3. The IEC 60947-2 DC tests that matter

DC rated breakers are proven to IEC 60947-2 with a stated rated DC voltage and a breaking capacity at that voltage. Look for the DC symbol and the staged test report, not an AC-only mark.

Technical diagram shown at a readable responsive scale.

4. Common procurement mistakes

• Buying an AC MCB for a DC string — silent, then catastrophic, failure.
• Ignoring polarity — mis-wired devices that will not clear.
• Undersizing the staged voltage — nuisance trips under open-circuit swing.

5. Where NEUTRON fits

NEUTRON DC MCBs are tested to IEC 60947-2, polarity marked, and rated up to 1000 V DC for PV combiner and BESS protection. CE and CB certified, IP20 to IP65.