Difference Between MCB, MCCB, RCCB, and ELCB
In electrical protection, MCB, MCCB, RCCB, and ELCB serve different purposes. This post explains how each device works, where to use it, and a simple selection guide you can apply on projects.
Quick Definitions
- MCB (Miniature Circuit Breaker): Protects circuits from overload and short-circuit faults (typically up to 100 A).
- MCCB (Moulded Case Circuit Breaker): Higher capacity protection with adjustable settings (typically 100–1600 A) for feeders and large loads.
- RCCB (Residual Current Circuit Breaker): Protects people from earth leakage (shock) by tripping on residual current (e.g., 30 mA, 100 mA).
- ELCB (Earth Leakage Circuit Breaker): Legacy earth-leakage device (voltage-operated type); largely replaced by RCCB/RCBO.
Working Principles
- MCB: Thermal bimetal trips on overload; magnetic coil trips instantly on short-circuit.
- MCCB: Same fundamental principle as MCB but with adjustable thermal/magnetic (or electronic) trip units and higher breaking capacity (Icu).
- RCCB: Compares current in phase and neutral via a toroidal CT. Any imbalance (> sensitivity) trips the device.
- ELCB: Voltage-operated device trips when potential between equipment body and earth exceeds a threshold. Sensitive to earth quality; superseded by RCCB.
Key Differences (Comparison Table)
| Parameter | MCB | MCCB | RCCB | ELCB |
|---|---|---|---|---|
| Primary Protection | Overload, Short-circuit | Overload, Short-circuit (adjustable) | Earth leakage / Shock | Earth leakage (voltage-operated) |
| Typical Current Rating | 0.5–100 A | 100–1600 A | 16–125 A (current), sensitivity 30/100/300 mA | 10–63 A (older types) |
| Breaking Capacity (Icu) | 6–10 kA (domestic), up to 25 kA (industrial) | 25–65 kA (and higher) | Not applicable (leakage device) | Not applicable (legacy) |
| Adjustable Trip | No | Yes (thermal/magnetic/electronic) | Sensitivity only (mA) | No |
| Neutral Requirement | 1P/2P/3P/4P variants | 3P/4P | 2P (1Φ) / 4P (3Φ) with neutral through device | Requires earth reference |
| Typical Use | Final circuits, DBs | Main incomers/feeders, large motors | Human protection, wet areas, sockets | Legacy installations |
| Standards | IEC 60898-1 / IS 8828 | IEC 60947-2 / IS 13947-2 | IEC 61008/61009 | Old national specs |
| Cost | Low | Medium–High | Low–Medium | Obsolete |
Trip Curves (MCB)
- Type B: Trips at 3–5 × In — suitable for resistive lighting and small loads.
- Type C: Trips at 5–10 × In — general purpose, motors, mixed loads.
- Type D: Trips at 10–20 × In — high inrush loads (transformers, large motors).
When to Use What? (Selection Guide)
- For outgoing final circuits: Use MCB with correct curve (B/C/D) and adequate Icu.
- For mains/feeder/protection >100 A: Use MCCB with adjustable trips and suitable breaking capacity.
- For shock protection: Use RCCB (30 mA for personal protection; 100/300 mA for fire protection upstream).
- Avoid new ELCB (replace with RCCB/RCBO in upgrades).
Applications
- Homes, offices: MCB + RCCB/RCBO on socket and wet areas.
- Industries: MCCB as incomer/feeder, selective coordination with downstream MCBs.
- Data centers/hospitals: Type A/Type B RCCB where VFDs or DC components exist.
FAQs
Q1. Can an RCCB replace an MCB?
No. RCCB does not protect against overload/short-circuit. It must be paired with MCB/MCCB.
Q2. What is RCBO?
An RCBO combines MCB (overload/short-circuit) and RCCB (leakage) in a single device.
Q3. Which RCCB sensitivity should I choose?
Use 30 mA for personal protection on final circuits; 100/300 mA upstream for fire protection/feeder-level.
Q4. How to size MCCB?
Match rated current to feeder load, check Icu ≥ prospective fault level, select adjustable trips to coordinate with downstream devices.
Conclusion
Use MCB for final circuits, MCCB for high-current feeders with coordination, and RCCB/RCBO for human protection. Avoid new ELCB installations. Correct selection improves safety, reliability, and compliance.
Post a Comment