Miniature breakers, molded-case breakers, and residual-current breakers sit in different places in a board. The RFQ should say the available fault current, the load, the curve, and whether people or fire protection require residual current. Tradinor does not treat the ampere printing as a complete order.
Three devices, three jobs
An MCB is the small frame. Its interrupt rating must still exceed the fault current at that bus. If the transformer can deliver more than the MCB can clear, the design needs a current-limiting upstream device or a larger frame. An MCCB is that larger frame. It may have adjustable thermal and magnetic trips. Write the settings you want dialed, or the study will be undone by the factory default.
An RCBO combines overcurrent and residual current. Specify the residual sensitivity, often 30 mA for personal protection or a higher value for fire, and the residual type the loads require. Drives and LED drivers leak and distort the waveform. The residual type has to match that load or the device trips with no fault. This is a purchasing match to the datasheet, not a medical claim.
- System voltage, poles, and continuous current.
- Interrupt rating above the available fault current.
- Curve or trip unit, including motor inrush.
- Residual current only if you need it: sensitivity and type.
- Accessories: auxiliary contact, shunt trip, or handle tie.
| Device | Use when | Extra line |
|---|---|---|
| MCB | Final circuits within its kA | Curve B, C, or D |
| MCCB | Higher current or higher fault level | Trip settings written down |
| RCBO | Overcurrent plus residual current | mA and residual type |
Check the printing
On the sample, read the interrupt rating and the curve code, not only the amperes. Confirm poles and that a residual device shows the milliamp rating you ordered. Ask for the datasheet page that states the interrupt rating at your voltage. A rating at 230 V is not automatically the rating at 400 V. Keep the coordination note with the upstream fuse or breaker if the board was designed as a pair.
What to lock on the order
Ask the board builder for the fault current at the bus and write it on the RFQ before you pick a frame. Then the ampere rating, the curve, and the poles are the second line, not the first. If residual current is required, add the milliamp rating and the type on that same line so a plain MCB cannot be substituted by someone matching only the amperes. Where an MCCB trip is adjustable, write the settings on the drawing and ask the factory to set them before shipment, with a mark or a record. Confirm accessories as separate part numbers. An auxiliary contact added later often needs a different dealer’s kit. On the sample, read every marking on the front of the device and compare it with the order. The interrupt rating is the one most often skipped because the ampere number is larger and easier to see.
Questions buyers actually ask
Is an MCCB just a large MCB?
It is a different frame, often with an adjustable trip and a higher interrupt rating. Use it when the fault level or the current exceeds what the miniature frame can clear.
What does an RCBO add?
Residual-current protection in the same device as overcurrent. You still specify the residual trip current and the type, and you still need the short-circuit rating.
Can I raise the ampere rating to stop nuisance trips?
Not as a habit. The cable and the load set the continuous rating. Nuisance trips usually mean inrush or leakage, which want a curve or a different residual type.