MCB vs MCCB: What's the Difference & How to Choose
17 August 2026 | NY Circuit Team
MCB (Miniature Circuit Breaker) and MCCB (Molded Case Circuit Breaker) both protect circuits from overload and short circuit — but they are built for very different jobs. Using the wrong one is either unsafe or expensive. Here is the practical difference.
Quick Answer
| MCB | MCCB | |
|---|---|---|
| Rated current | Up to 125A | 10A to 1600A+ |
| Breaking capacity | Up to 10–15kA | 25kA to 100kA+ |
| Poles | 1P–4P | 3P, 4P |
| Trip adjustment | Fixed | Adjustable (thermal-magnetic or electronic) |
| Typical use | Final circuits, lighting, sockets | Distribution, motor feeders, main boards |
Our STM6 MCCB line starts at 16A and covers frames up to 2000A — see the full STM6 specification table for frame sizes and breaking capacities.
1. Current Rating
MCBs are compact devices designed for final circuits — lighting, sockets, small motors — typically rated 6A to 125A.
MCCBs start where MCBs end: standard frames run from 63A up to 1600A and beyond. If your circuit carries more than 100A, an MCCB is almost always the right choice.
2. Breaking Capacity (The Big One)
Breaking capacity (Icu) is the maximum fault current the breaker can safely interrupt. A short circuit on a main distribution board can easily exceed 25kA — far beyond any MCB.
- MCB: typically 6kA or 10kA — fine at the far end of an installation where cable impedance limits fault current.
- MCCB: 25kA to 100kA — required close to transformers, on main boards and for large loads.
Rule of thumb: the closer you are to the transformer, the higher the required breaking capacity — and that means MCCB.
3. Trip Unit Adjustability
- MCBs use a fixed thermal-magnetic trip — simple, reliable, no tuning.
- MCCBs offer adjustable thermal settings and electronic trip units with programmable LSI curves. This allows selectivity: the downstream breaker trips first, keeping the rest of the installation running.
4. Physical Size and Price
An MCB fits on a DIN rail and costs a few dollars. An MCCB is a much larger device with a molded case, often mounted on a backplate or in a draw-out cradle — and costs accordingly. Buying an MCCB where an MCB works wastes budget; buying an MCB where an MCCB is needed risks a catastrophic failure.
5. Common Applications
MCB — residential and commercial final circuits, lighting panels, socket outlets, small HVAC units.
MCCB — main distribution boards, motor feeders above 15kW, generator outputs, UPS systems, industrial panels, solar combiner boxes.
Which One Do You Need?
Ask three questions:
- What is the load current? (>125A MCCB)
- What is the prospective short-circuit current at the installation point? (>10kA MCCB)
- Do you need adjustable protection or selectivity? (Yes MCCB with adjustable trip)
Our listed STM series includes multiple frame and breaking-capacity options. A retrofit comparison with CHINT, ABB, Schneider or another brand must use the exact dimensions, terminals, trip characteristics and application requirements. Check the circuit-protection range