Do not assume an AC-only miniature circuit breaker can protect a DC circuit. Use a breaker only when the exact model has a documented DC rating for the system voltage, pole arrangement and polarity, and when its DC breaking capacity is adequate for the circuit’s prospective short-circuit current. The same ampere rating or DIN-rail format does not prove compatibility.
| Evidence for the exact model | Result | Next action |
|---|---|---|
| A current manufacturer document gives a DC rating that covers the required conditions | Potentially suitable | Complete all seven checks before specifying it |
| The model is marked and documented only for AC | Not confirmed for DC | Select a documented DC-rated model |
| The marking, suffix or documentation is unclear | Unconfirmed | Stop and request written confirmation for the complete model code |
The decisive question is not whether an AC breaker can be “derated” by a general rule. It is whether the manufacturer has documented the exact model for the intended DC duty and whether the circuit conditions stay within that rating.
A valid review therefore needs two evidence sets: current product information for the exact breaker and actual electrical data for the circuit. A catalog description without circuit inputs is incomplete, and circuit data without a traceable product rating is equally insufficient.
Rated current, rated operational voltage and breaking capacity describe different parts of breaker performance. A 32 A AC MCB and a 32 A DC MCB may share a normal-current value, but that does not make their voltage or fault-interruption duties interchangeable.
AC current naturally passes through zero during each cycle, which assists arc extinction when contacts open. DC does not provide the same natural current-zero condition. The breaker design and the manufacturer-approved application arrangement must therefore be suitable for the stated DC voltage and fault duty.
Official MCB guidance from Schneider Electric treats voltage, short-circuit conditions, earthing and pole implementation as connected selection inputs. ABB’s DC wiring guidance for miniature circuit breakers also shows that permitted DC voltage and connection arrangements depend on the product family and configuration. These are manufacturer-specific examples, not universal rules for other brands.
This is a specification and document review, not an installation procedure.
Record the complete model code, including every suffix. Similar enclosures and neighboring products in a catalog can carry different AC/DC ratings. A family name alone is not enough to approve a particular device.
If a distributor proposes an alternative, repeat the review for that exact model rather than transferring the conclusion from the original selection.
Look for an explicit DC voltage rating and confirm that the label belongs to the same model code shown in the current technical documentation. Review the product marking and manufacturer documents together; neither a partial label photograph nor an informal verbal assurance should override a model-specific condition.
If the documents conflict, are incomplete or cannot be traced to the manufacturer, treat compatibility as unconfirmed and request written clarification.
Confirm the maximum DC system voltage, not just its typical operating value. Also identify the voltage between each conductor and earth. Earthing arrangements can change the duty across individual poles during normal operation or a fault.
Do not copy a voltage limit from another manufacturer or breaker family. The applicable limit is the one documented for the selected model and permitted configuration.
Some DC ratings depend on how many poles are used, how those poles are connected and whether supply polarity must be observed. Other models may have different conditions. Follow only the diagram and instructions for the exact model.
There is no safe universal instruction such as “always use two poles” or “polarity never matters.” A valid arrangement for one product family may be invalid for another.
Prospective short-circuit current is a characteristic of the circuit. DC breaking capacity is a documented device capability under stated test and application conditions. The applicable DC breaking capacity must be adequate for the calculated prospective short-circuit current at the installation point.
Do not reuse an AC breaking-capacity value as if it were a DC value. If the DC value or its conditions are missing, the selection is incomplete.
Check that the rated current and trip characteristic suit the conductor, load and protection objective. Also review the manufacturer’s environmental, installation and application limits. A familiar curve letter does not by itself establish DC compatibility.
Converter-fed systems, batteries, photovoltaic circuits and other DC sources can have different fault-current behavior. The protection study must use the actual source and circuit conditions rather than a generic product assumption. ABB’s broader technical paper on protection devices for DC applications discusses these system-level differences and includes a dedicated MCB section.
Before ordering, identify the data sheet, installation instructions, test reports or certificates required by the project. Confirm that every document refers to the complete model being quoted and that the project team has reviewed the applicable local requirements.
A product standard or certificate is evidence about a defined scope; it is not, by itself, approval for an undisclosed circuit or installation.
| Error | Why it fails | Better action |
|---|---|---|
| Comparing only ampere ratings | Rated current does not establish DC voltage or interruption performance | Compare the complete DC rating and circuit duty |
| Applying an AC kA value to DC | Breaking capacity is conditional on the stated duty | Use the documented DC value for the exact model and arrangement |
| Inferring compatibility from appearance | Similar housings can contain products with different ratings | Match the complete model code, marking and documents |
| Selecting before collecting circuit data | The supplier cannot verify an undisclosed duty | Send the full RFQ inputs before requesting a model |
A complete request reduces repeated clarification and makes model confirmation more reliable.
| RFQ field | Why it matters |
|---|---|
| Destination market and project type | Defines the document and application context |
| Maximum DC system voltage and voltage to earth | Supports voltage and pole review |
| Rated load current | Provides the normal-current input |
| Prospective short-circuit current | Allows comparison with DC breaking capacity |
| Required pole configuration | Helps identify the correct product version |
| Earthing or system arrangement | Provides fault and voltage context |
| Load or application type | Supports trip and application review |
| Quantity and packaging | Supports the commercial quotation |
| Required data sheet, report or certificate | Defines the evidence needed before approval |
| Proposed model code and label photo, if available | Enables an exact-model check |
OOHMAGE’s miniature circuit breaker range presents separate AC and DC product paths, including the OMC8 AC and OMC8-DC series. That separation is a starting point for product review, not proof that a model suits an unspecified circuit.
Send the circuit conditions and required documents through the OOHMAGE contact page so the team can check a documented model before quotation. Do not rely on a generic request such as “63 A breaker for DC.”
This article does not replace short-circuit calculations, protection coordination, conductor selection, installation design or review against applicable local requirements. It does not provide terminal wiring or live-testing instructions and does not approve a breaker for an undisclosed circuit.
Final device selection should be reviewed by qualified electrical personnel using the marking and current manufacturer documentation for the exact model.
Not on the basis of current rating alone. The exact model needs a documented DC rating covering the system voltage, poles, polarity where applicable and DC breaking capacity. That breaking capacity must then be checked against the circuit’s prospective short-circuit current. If the model is documented only for AC, do not assume its AC rating transfers to DC.
Yes. A manufacturer may document separate AC and DC duties for the same model. Apply each rating only within its stated conditions. Confirm the complete code, voltage, pole arrangement, polarity conditions, breaking capacity and relevant instructions.
No. Rated current concerns the current a breaker carries under specified operating conditions. Breaking capacity concerns the fault current it can interrupt under specified conditions. A selection needs an appropriate rated current and adequate DC breaking capacity.
Do not decide AC/DC compatibility from ampere rating, enclosure size or a general derating rule. Start with the complete model code, then verify the documented DC voltage, pole and polarity conditions, trip characteristic and application limits. Finally, compare the model’s DC breaking capacity with the circuit’s prospective short-circuit current. If any input or document is unclear, stop the selection and obtain written confirmation before ordering.
