100A Frame
In moulded case circuit breakers (MCCBs), “100A” refers to the maximum rated current the breaker can carry continuously without tripping. The frame size, however, is about the physical envelope and mechanical design of the breaker — its dimensions, terminal capacity, and accessory compatibility.
Key distinctions
- Rated current (In)
- Defines the continuous current that the breaker can protect.
- For a 100 A MCCB, the trip unit is set to protect loads up to 100A.
- Frame size
- Refers to the mechanical housing and design class of the breaker.
- Determines terminal size, mounting footprint, and which accessories (auxiliary contacts, shunt trips, communication modules) can be fitted.
- A “100A frame” is physically smaller than 250 A, 400 A, or 630 A frames, and is optimised for lower current feeders.
Practical implications
| Aspect | 100A MCCB | Larger frames (250–630A) |
|---|---|---|
| Physical size | Compact, narrow width | Larger, wider, heavier |
| Typical use | Small feeders, branch circuits | Main feeders, larger motors |
| Breaking capacity | Adequate for lower fault levels | Higher kA ratings available |
| Accessories | Limited but sufficient (aux contacts, shunt trip) | Wider accessory range, advanced trip units |
| Integration | Fits compact distribution boards | Requires more panel space |
Selection checklist
- Load current: Ensure breaker rating ≥ continuous load current.
- Fault level: Verify Icu/Ics (breaking capacity) ≥ prospective fault current at installation point.
- Trip unit type: Thermal/magnetic for simple feeders; electronic trip units for adjustable protection and monitoring.
- Panel fit: Confirm dimensions and busbar/cable compatibility with the 100A frame.
- Accessories: Choose auxiliary contacts or communication modules if monitoring or interlocks are required.
Best practices
- Consult datasheets: Manufacturers (e.g., Schneider Electric’s ComPacT NSX100) provide exact dimensions, torque values, and accessory compatibility.
- Coordination study: Ensure selectivity with upstream MCCBs or ACBs.
- Maintenance: Periodic mechanical operation checks, contact inspection, and thermal imaging under load.
