Solar & DC

DC MCB & MCCB Rating Calculator (PV & Battery)

Screen the rated current, DC operating voltage, pole configuration, and breaking capacity for a DC circuit breaker on a PV array or battery circuit. DC breakers are not AC breakers derated — the voltage rating and pole arrangement are DC-specific and must come from the device documentation.

Circuit

Array I_sc (A)

System voltage V_dc (V)

Cable capacity I_z (A) optional

Prospective fault (kA) optional

ⓘFor PV the continuous current is the array short-circuit current I_sc; for a battery or DC load it is the maximum continuous load current.

Minimum rated current I_n

— A

Rated voltage U_e

—

Poles (in series)

—

Checks

—

How the rating is built

Rated current: I_n ≥ 1.25 × continuous current Rated voltage: U_e ≥ system V_dc (PV: cold V_oc) Cable rule: I_n ≤ I_z

The 1.25 factor is the continuous-duty margin — for PV it also covers irradiance and temperature above STC. The rated voltage must cover the highest DC voltage the circuit can reach, which for a PV string is the cold-temperature open-circuit voltage, not the nominal system voltage.

Why DC poles matter

Interrupting DC is harder than AC because there is no natural current zero to help extinguish the arc. Manufacturers achieve a DC voltage rating by connecting poles in series so each pole shares the arc voltage. A breaker rated, say, 250 V per pole may need two poles in series for a 500 V circuit and four for 1000 V. The pole count and the required internal connection are stated by the manufacturer — never assume an AC breaker will interrupt the same DC voltage.

⚠DC rating is not AC rating. An AC MCB/MCCB used on DC without a DC voltage rating and the correct series-pole wiring may fail to clear the arc. Use a device explicitly DC-rated for the voltage, or the PV-specific series.

Frequently asked questions

What voltage rating do I need for a 1000 V PV string?

At least the cold-temperature string open-circuit voltage, which can exceed 1000 V on a cold morning. Use a breaker rated for that DC voltage with the manufacturer’s specified pole configuration.

Does a PV string with only two strings need a breaker?

A breaker or disconnector is still needed for isolation, but over-current protection between paralleled strings is only required once enough strings are combined to drive a damaging reverse current — see the string-fuse guidance.

Can I use a standard MCCB on a battery circuit?

Only if it carries a DC voltage rating covering the battery voltage and the required pole arrangement. Battery fault currents can be very high, so the DC breaking capacity must also cover the prospective fault.

Select the DC breaker

Match the rated current, DC voltage, poles, and breaking capacity to a DC-rated device for the array or battery.

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Standards referencedIEC 60947-2 (circuit-breakers) · IEC 60364-7-712 (PV) · IEC 62548 (PV array design) · manufacturer DC ratings.

Screening estimate for guidance only. The final DC breaker current, voltage, pole configuration, and breaking capacity must be confirmed by a qualified person against the manufacturer’s DC data and the circuit fault level.