How to size a molded case circuit breaker (MCCB): frame size, breaking capacity, thermal-magnetic vs electronic trip, and pole count for panel builders.
An MCCB (molded case circuit breaker) is the larger sibling of the miniature circuit breaker you fit on a DIN rail. Where an MCB tops out around 125 A, an MCCB covers from roughly 10 A up to 1600 A in a single moulded-insulation case, with a breaking capacity an order of magnitude higher. This guide is for panel builders, specifiers and distributors who have to put a frame size, a trip unit and a breaking capacity on the order rather than just a current.
An MCCB is sold by its frame size — the maximum rating of the case — and then adjusted down to the trip setting you need. A 100 A frame might be ordered with a 16, 25, 32, 50, 63, 80 or 100 A thermal setting; a 250 A frame covers 100–250 A, and so on. Pick the frame at or just above the protected load's full-load current, then set the trip to the circuit value. Buying the next frame up only costs money and space, so size the frame to the load, not to a guessed maximum.
| Frame size | Typical adjustable trip range | Common use |
|---|---|---|
| 100 A | 16–100 A | Sub-distribution, large motor feeds, machine mains |
| 250 A | 100–250 A | Small switchboards, genset tie, feeder pillars |
| 400 A | 250–400 A | Main incoming to a floor or small building |
| 630 A | 400–630 A | Main switchboard incoming, large plant |
| 800 A and above | up to 1600 A | Main incomer, busbar coupling |
Two figures matter. Icu is the ultimate breaking capacity — the fault current the breaker can interrupt once without being destroyed. Ics is the service breaking capacity — what it can clear and still be put back into service, usually expressed as a percentage of Icu (commonly 50 % or 100 %). At the main incomer of an industrial board the prospective fault current can be tens of kiloamps, so specify Icu at or above that figure and confirm Ics if the breaker must stay in service after a fault. A 25 kA or 36 kA Icu frame is typical for a building main; a 50 kA or 65 kA frame belongs near a transformer or generator.
The trip unit decides how the breaker senses an overcurrent.
| Thermal-magnetic | Electronic (microprocessor) | |
|---|---|---|
| Adjustment | Fixed or limited bands | Wide, settable via dial or display |
| Protection | Overload + short-circuit | Overload + S/C + ground-fault + optional alarms |
| Accuracy | Good | High, stable over temperature |
| Cost | Lower | Higher, but fewer spares to stock |
| Best for | Standard feeders, motor circuits | Main incomers, selective schemes, data centres |
For most distribution and motor feeders a thermal-magnetic unit is enough. Choose electronic when you need precise, repeatable settings, integrated ground-fault protection, or communication with a power-management system.
MCCBs come in 1, 2, 3 and 4-pole versions. Three-pole is the default for three-phase feeders and motors; four-pole (including the neutral) is required where the neutral must be switched or isolated — for example on an isolation point, a generator changeover, or a TN-S/TT system where the neutral is part of the protected circuit. Match the pole count to the earthing and switching requirement, not just to the phase count.
| MCB | MCCB | |
|---|---|---|
| Current range | up to ~125 A | 10 A to 1600 A |
| Breaking capacity | 6–10 kA typical | up to 65 kA and beyond |
| Adjustable trip | Fixed by type B/C/D | Adjustable thermal setting |
| Mounting | 35 mm DIN rail | Bolted or DIN-adapted, larger case |
| Trip unit | Thermal-magnetic only | Thermal-magnetic or electronic |
| Use | Final circuits, sub-boards | Feeders, mains, motor protection |
An MCCB does not replace a contactor or an overload relay on a motor, and it must coordinate with the device upstream. Check the manufacturer's selectivity tables so a downstream fault opens the local breaker and not the main incomer — keeping the rest of the board alive. Where the MCCB protects a motor, pair it with a thermal overload relay or use a motor-protective MCCB with an adjustable magnetic setting, and confirm the combination is tested for type coordination.
ELEHPD supplies molded case circuit breakers from 16 A to 630 A frames, with thermal-magnetic and electronic trip units, in 2-, 3- and 4-pole versions and breaking capacities up to 50 kA, plus the shunt trips, auxiliary contacts and undervoltage releases needed for a complete feeder or incomer.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.