What is the Key Difference Between RCCB and MCB?
RCCB（残留電流サーキットブレーカー）
An RCCB monitors the current flowing through live and neutral wires. When it detects an imbalance (indicating current is leaking to ground), it immediately disconnects the circuit within 30 milliseconds. This protects against:
- Electrical shock to humans
- 地絡 fires
- Equipment damage from insulation failure
MCB（ミニチュアサーキットブレーカー）
An MCB protects against excessive current flow in circuits. It trips when current exceeds the rated limit, protecting against:
🚨 安全警告: MCBs cannot detect current leakage to ground. A person can receive a fatal shock from a circuit protected only by MCB if current finds an alternate path through their body to ground.
Comprehensive RCCB vs MCB Comparison Table
| 特徴 | RCCB | エムシービー |
|---|---|---|
| 一次保護 | Earth leakage current (30mA or less) | Overcurrent and short circuit |
| 検出方法 | Current imbalance between live/neutral | Excessive current flow |
| 旅行時間 | 30 milliseconds | 0.1～3秒 |
| Shock Protection | ✅ Excellent (life-saving) | ❌ None |
| 防火 | ✅ Ground fault fires | ✅ Overload fires |
| Code Requirement | Mandatory in wet areas | Mandatory for all circuits |
| リセット方法 | 手動リセットボタン | Manual lever reset |
| コスト | 高いイニシャルコスト | イニシャルコストの低減 |
| テスト | Monthly test button | 目視検査 |
When You Must Use RCCB Instead of MCB
Critical Safety Applications
1. Wet and Damp Locations
- Bathrooms and shower areas
- キッチンカウンターのコンセント
- Laundry rooms
- Basement areas prone to moisture
2. Outdoor Electrical Circuits
- Garden lighting and power outlets
- プール＆スパ用品
- Outdoor cooking areas
- Garage door openers
3. High-Risk Areas
- Children’s bedrooms and play areas
- Elderly care facilities
- Workshops with handheld power tools
- Any circuit with portable equipment
Expert Tip: Combined Protection Strategy
Most electrical experts recommend using RCCBs in conjunction with MCBs, not instead of them. This provides comprehensive protection against both overcurrent and ground faults.
How RCCB Protection Saves Lives: Real-World Examples
Scenario 1: Bathroom Safety
When you use a hair dryer in the bathroom, if water enters the device and creates a path to ground through the metal frame, an RCCB will detect the 30mA current leakage and trip instantly. An MCB would not detect this condition, allowing potentially fatal current to flow through anyone touching the device.
Scenario 2: Outdoor Power Tools
Using an electric hedge trimmer outdoors, if the blade cuts through the power cord and touches your hand, the RCCB detects the current flowing through your body to ground and trips within 30 milliseconds – faster than your heart can go into fibrillation.
Scenario 3: Kitchen Appliance Faults
If a microwave oven develops internal insulation failure, causing current to leak to its metal case, an RCCB prevents electrocution when someone touches the appliance. The MCB would only trip if there was a complete short circuit.
RCCB Selection Criteria: Expert Guidelines
Sensitivity Ratings
| RCCB Type | 感度 | 申し込み |
|---|---|---|
| 30mA | High sensitivity | Personal protection (required) |
| 100mA | Medium sensitivity | Fire protection only |
| 300mA | Low sensitivity | Industrial equipment protection |
Time-Delay Classifications
- Instantaneous (0ms): General residential use
- Short delay (10ms): Reduces nuisance tripping
- Selectable delay: Industrial applications with coordination needs
Step-by-Step RCCB Installation Guidelines
⚠️安全警告: RCCB installation must be performed by qualified electricians in accordance with local electrical codes (NEC in US, IEC internationally).
インストールプロセス:
- 主電源を切る 電気パネルで
- 電源がオフになっていることを確認する using a non-contact voltage tester
- Mount RCCB in appropriate panel position according to manufacturer specs
- Connect incoming supply to RCCB line terminals
- Connect outgoing circuits to RCCB load terminals
- テスト運用 using the built-in test button
- Restore power and verify normal operation
- Document installation for maintenance records
コードコンプライアンス要件
- NEC 210.8: GFCI/RCCB protection required for bathrooms, kitchens, outdoors, crawl spaces, and unfinished basements
- IEC 61008: International standard for RCCB performance and testing
- Local amendments: Check with local authority having jurisdiction
Common RCCB Problems and Troubleshooting
頻繁に起こる迷惑なつまずき
原因がある：
- Moisture in wiring or connections
- Damaged cable insulation
- Equipment with high leakage current
- Incorrect sensitivity rating
解決策:
- Inspect and dry all connections
- Test cable insulation with megohmmeter
- Use time-delayed RCCB for equipment with natural leakage
- Upgrade to appropriate sensitivity rating
Test Button Doesn’t Work
原因がある：
- Internal mechanism failure
- Corroded contacts
- End of service life (typically 10-15 years)
解決策:
- Replace RCCB immediately – non-functional test indicates protection failure
- 専門家による検査のスケジュール
- Upgrade to current technology RCCB
専門家のヒント: Test your RCCB monthly using the test button. If it doesn’t trip immediately, the device has failed and provides no protection.
Professional Recommendations for RCCB vs MCB Selection
Use RCCB When:
- Human contact with electrical equipment is possible
- Circuits serve wet or outdoor locations
- Portable equipment is connected
- Building codes require ground fault protection
- Maximum safety is the priority
Use MCB When:
- Protecting fixed equipment with no human contact
- Industrial motor circuits (with appropriate ground fault protection upstream)
- Lighting circuits in dry locations
- Fire alarm and emergency systems (where nuisance tripping is critical)
Use Both (RCCB + MCB) When:
- Comprehensive protection is needed
- Code requires both overcurrent and ground fault protection
- Critical safety applications
- 商業施設および工業施設
Quick Reference: RCCB Installation Checklist
Pre-Installation:
- [ ] Verify local code requirements
- [ ] Calculate load requirements
- [ ] Select appropriate sensitivity (typically 30mA)
- [ ] Obtain necessary permits
During Installation:
- [ ] Power disconnected and verified
- [ ] Proper mounting and connections
- [ ] Correct wire sizing and routing
- [ ] Test button operation verified
Post-Installation:
- [ ] System testing completed
- [ ] User education provided
- [ ] Monthly testing schedule established
- [ ] Documentation completed
よくある質問
Can I replace an MCB with an RCCB?
Yes, but you should consult a qualified electrician. The RCCB must have the same or higher current rating as the MCB it replaces, and you need to ensure compatibility with your electrical panel and local codes.
Why does my RCCB trip when it rains?
Rain can cause moisture infiltration into outdoor electrical connections or damaged cable insulation. This creates a path for current to leak to ground, which the RCCB correctly detects as a safety hazard.
How often should I test my RCCB?
Test monthly using the built-in test button. The device should trip immediately when tested. If it doesn’t trip, replace it immediately as it’s not providing protection.
Can I use a 100mA RCCB instead of 30mA?
For personal protection, 30mA is required. 100mA RCCBs are only suitable for fire protection, not shock protection, as 100mA can still be fatal to humans.
What’s the difference between RCCB and GFCI?
They’re essentially the same device with different names. GFCI（漏電遮断器） is the North American term, while RCCB is the international terminology.
Do I need RCCB protection for LED lighting?
While not always required for fixed LED lighting in dry locations, RCCB protection is recommended for any lighting circuit where maintenance involves human contact or in areas prone to moisture.
結論：電気安全のための正しい選択
The decision to use RCCB instead of MCB isn’t about replacement – it’s about proper protection for specific applications. RCCBs save lives by detecting dangerous current leakage that MCBs cannot detect, making them essential for any circuit where human safety is at risk.
For comprehensive electrical protection, work with qualified electricians who understand both local codes and safety best practices. The small additional cost of RCCB protection is insignificant compared to preventing electrical shock, fire, or loss of life.
関連
MCB、MCCB、RCB、RCD、RCCB、RCBOの違いは何ですか？ 2025年版
