How to Choose an RCCB

A practical buying & installation guide for LS ELECTRIC RKN / RKN-b residual current circuit breakers

How to Choose an RCCB

Why this matters

An RCCB (Residual Current Circuit Breaker) protects people from electric shock caused by earth leakage current. It continuously compares the current flowing in the phase and neutral conductors; when a leakage (e.g., through a human body to earth) exceeds the trip threshold, the RCCB disconnects the circuit immediately, preventing fatal shock and reducing fire risk from insulation faults.

Unlike MCB/MCCB/ACB—which protect against overload and short-circuit—an RCCB does not provide overcurrent protection. Therefore, in any panel the RCCB must be paired with an upstream overcurrent protective device (OCPD) such as an MCB or MCCB to form a complete protective scheme.

For residential, commercial, and light-industrial applications, LS ELECTRIC’s RKN (63AF frame) and RKN-b (63AF / 100AF frame) families are the go-to options. The official RCCB Instruction Manual summarizes the core ratings (In, voltage, leakage trip levels, operation type A/AC), conditional short-circuit capacity (6 kA or 10 kA), 35 mm DIN-rail mounting, terminal styles, compliance (SEMKO CB / IEC 61008-1), circuit diagrams, 4-pole-as-2-pole wiring, TEST procedure, tightening torque, safety cautions, and outline dimensions. [RCCB] 사용설명서_Manual_EN_202502

Understand the LS ELECTRIC RCCB ratings (with manual cross-checks)

1) Rated current (In) & frame size

• RKN (63AF frame): 25 / 32 / 40 / 63 A
• RKN-b: 63AF frame (25–63 A) and 100AF frame (80 / 100 A)

Select In from the load’s design current, and verify proper selectivity/coordination with the upstream MCB/MCCB. [RCCB] 사용설명서_Manual_EN_202502

2) Rated system voltage

• 1P+N: 240 V AC (residential/office)
• 3P+N: 415 V AC (commercial/industrial)

For 3-phase systems without a neutral, the manual shows how to interconnect terminals “4” and “8” so a 4-pole RCCB behaves as a 2-pole device while keeping the internal differential sensing correct. Follow the illustrated connection scheme exactly. [RCCB] 사용설명서_Manual_EN_202502

3) Residual operating current (IΔn) & non-operating current

• Operating (trip) current IΔn: 30 / 100 / 300 mA
• Non-operating current: 15 / 50 / 150 mA (below which the device must not trip)

Rules of thumb:

• 30 mA → people protection (general outlets, bathrooms, public spaces)
• 100–300 mA → fire protection / feeder supervision (industrial lines, long cables, high cumulative leakage) [RCCB] 사용설명서_Manual_EN_202502

4) Operation type (A vs AC)

• Type AC: trips on sinusoidal AC leakage (basic loads).
• Type A: trips on AC + pulsating DC leakage (inverter drives, switch-mode supplies, induction cookers, modern appliances).
  Given today’s electronics-heavy loads, Type A is recommended for most circuits; use Type B RCDs for EV chargers/PV where smooth DC can occur (Type B is outside RKN/RKN-b scope). [RCCB] 사용설명서_Manual_EN_202502

5) Conditional short-circuit capacity (withstand with upstream OCPD)

• RKN: 6 kA
• RKN-b: 10 kA

The manual stresses coordination with an upstream MCB/MCCB (e.g., 63 A device for 6 kA circuits, 100 A for 10 kA). In such coordinated schemes the OCPD can substitute for a fuse to protect the RCCB during high-fault events. [RCCB] 사용설명서_Manual_EN_202502

6) Mounting & terminals

• 35 mm DIN-rail snap-on mounting (install/remove as illustrated).
• Terminals:
  • RKN: lug type, cable up to 25 mm²
  • RKN-b: dual (lug & screw), cable up to 35 mm²
• Terminal screws: M5 (63AF), M6 (100AF)
• Tightening torque (typical per manual): M5 ≈ 2.0 N·m, M6 ≈ 2.5 N·m

Use the manual’s wiring-capability table as a guide (e.g., ~4 mm² for 25 A; 6 mm² for 32 A; 10 mm² for 40 A; 16 mm² for 50/63 A; ≥25 mm² for 80–100 A) and adapt to national codes and installation conditions. [RCCB] 사용설명서_Manual_EN_202502

7) Standards

Compliance: SEMKO CB / IEC 61008-1 (RCCBs for household and similar use). [RCCB] 사용설명서_Manual_EN_202502

A 7-step selection workflow (RKN / RKN-b)

Step 1 — Identify the network: 1P+N 240 V or 3P+N 415 V (or 3P without N). Choose 2-pole or 4-pole accordingly. For 3-phase without N, apply the 4-to-2-pole interconnection (terminals 4 & 8) as shown in the wiring diagram. [RCCB] 사용설명서_Manual_EN_202502

Step 2 — Choose IΔn:

• 30 mA for personnel protection near users/outlets/wet areas
• 100–300 mA for feeder/fire protection and long runs with higher leakage [RCCB] 사용설명서_Manual_EN_202502

Step 3 — Choose type: A for electronic/inverter loads, AC for simple resistive/inductive circuits. [RCCB] 사용설명서_Manual_EN_202502

Step 4 — Choose In & frame: RKN 25–63 A or RKN-b 25–100 A as the circuit requires. Avoid oversizing (poor coordination) or undersizing (overheating terminations). [RCCB] 사용설명서_Manual_EN_202502

Step 5 — Check conditional short-circuit capacity:

• 6 kA circuits → RKN + upstream 63 A MCB/MCCB
• 10 kA circuits → RKN-b + upstream 100 A MCB/MCCB
  Coordination details and “can also be used instead of a fuse” note appear in the manual’s operation/safety pages. [RCCB] 사용설명서_Manual_EN_202502

Step 6 — Verify cable size & torque: Follow the table and tighten to M5 ≈ 2.0 N·m / M6 ≈ 2.5 N·m to prevent hot spots or loosening. [RCCB] 사용설명서_Manual_EN_202502

Step 7 — Confirm space & layout: Use the dimension drawings (RKN, RKN-b 63AF, RKN-b 100AF) to reserve rail space, bending radius, and working clearance. [RCCB] 사용설명서_Manual_EN_202502

Installation, wiring & commissioning (per manual)

Mounting on 35 mm DIN-rail

Clip on/off as illustrated. Ensure a flat, firm, dry panel and avoid excessive vibration. [RCCB] 사용설명서_Manual_EN_202502

Electrical connections

• Observe LINE/LOAD orientation—do not swap.
• For 4P used as 2P, bridge terminals 4 & 8 exactly as shown.
• Respect cable size/termination limits (RKN up to 25 mm², RKN-b up to 35 mm²) and the specified torque.
• Follow the manual’s note on correct parallel conductor routing at terminals. [RCCB] 사용설명서_Manual_EN_202502

Functional TEST

With supply present: set the handle ON, press the TEST button. The RCCB must trip immediately (handle returns to OFF). Perform this functional test at regular intervals. Record results during commissioning. [RCCB] 사용설명서_Manual_EN_202502

Short-circuit coordination

• RKN (6 kA): use with 63 A circuit breaker upstream
• RKN-b (10 kA): use with 100 A MCB/MCCB upstream
  Per manual, such coordination may substitute a fuse as SCPD to protect the RCCB under high fault. [RCCB] 사용설명서_Manual_EN_202502

What not to do

• Do not open or modify the breaker (warranty voids).
• Do not install in places with shock, high temperature, humidity, dust, corrosive gas, or excessive vibration.
• Use within the nameplate voltage/current; otherwise malfunction may occur.
• Ground equipment properly. If the RCCB trips, remove the cause before re-energizing—switching back on repeatedly can lead to fire.
• Do not touch live terminals or two live conductors at once; isolate upstream before any work. [RCCB] 사용설명서_Manual_EN_202502

Typical applications & recommended set-ups

Residential/Small office (1P+N 240 V)

• Floor/zone outlet groups: 2-pole 40–63 A, 30 mA, Type A
• Bathrooms/kitchens/mobile appliances: 30 mA at branch level, or individual RCBO 30 mA for critical socket lines.

Commercial buildings (3P+N 415 V)

• Floor distribution boards: 4-pole 63 A, 30 mA, Type A for outlets/lighting.
• HVAC or large equipment feeders: 100–300 mA to avoid nuisance tripping while maintaining fire protection.

Workshops/Light industry

• Maintenance sockets, wet areas: 30 mA.
• Long cable runs or drives with VFDs/inverters: 100–300 mA Type A at sub-board, with 30 mA on user-accessible circuits.

3-phase systems without neutral

• Use 4-pole RCCB and bridge 4 & 8 as shown in the diagram; verify the internal differential CT sees the correct current path before energizing. [RCCB] 사용설명서_Manual_EN_202502

Common mistakes that cause nuisance trips—or no trip at all

1. Grouping too many electronic loads (VFDs/SMPS) on a single 30 mA RCCB → cumulative leakage trips the device. Split into several RCCBs, use Type A, consider 100 mA at the upstream level with 30 mA at points of human contact.
2. Neutral mixing across different RCCB circuits → instantaneous tripping when loads run. Keep each RCCB’s N isolated to its own circuit.
3. Failing to bridge 4-8 when using 4-pole as 2-pole (or mis-ordering poles) → false imbalance.
4. Ignoring torque/cable size limits → hot terminals, carbonization, false leakage or damage.
5. Skipping regular TEST operations → mechanism may stick (dust/moisture), reducing protection.
6. Installing in harsh environments against cautions (humidity/corrosive dust/vibration) → surface leakage, oxidation, intermittent faults. [RCCB] 사용설명서_Manual_EN_202502

Commissioning & periodic maintenance (best practice)

• Pre-energization checks: verify nameplate (In, IΔn, type, poles, voltage), terminal tightness, cable sections, and the wiring diagram from the manual. [RCCB] 사용설명서_Manual_EN_202502
• Functional TEST: ON → press TEST → device must trip to OFF. Repeat 2–3 times and log the results. Perform at regular intervals thereafter. [RCCB] 사용설명서_Manual_EN_202502
• Trial under load: (if instruments available) measure background leakage; simulate a safe leakage to observe trip behavior.
• Periodic maintenance (monthly/quarterly): clean the board, press TEST, re-torque terminals (M5/M6), verify earthing, thermal-scan terminations if possible.
• If the RCCB trips spontaneously: locate and remove the cause (moisture ingress, insulation fault, neutral mixing) before switching ON again; the manual warns that re-energizing without fixing the cause can lead to fire. [RCCB] 사용설명서_Manual_EN_202502

Quick decision ma

• Homes/Apartments: 2P 40–63 A, 30 mA Type A per floor/zone; use individual RCBO 30 mA for bathrooms or critical sockets.
• Offices/Retail: 4P 40–63 A, 30 mA Type A on outlets; add RCCB 30 mA for LED-driver lighting where people interact.
• Commercial towers: 100 mA Type A at floor DB incomers; 30 mA downstream for people protection on sockets.
• Factories/Workshops: 100–300 mA Type A at sub-boards serving VFD-heavy/long-cable feeders; 30 mA on user-exposed circuits.
• 3-phase without neutral: use 4P with 4–8 bridge exactly as shown in the manual. [RCCB] 사용설명서_Manual_EN_202502

Final notes on mechanical layout & space

Refer to the dimension drawings for RKN, RKN-b 63AF, and RKN-b 100AF to plan rail width/height, side/top clearances, and cable bend radius. Keep the enclosure dry and ventilated, and avoid shock/vibration/heat/corrosive gases per the CAUTION notes. [RCCB] 사용설명서_Manual_EN_202502

Choosing an LS ELECTRIC RCCB is more than picking “30 mA vs 100 mA.” It’s a complete engineering decision spanning voltage & poles, type (A/AC), IΔn, In, conditional short-circuit capacity (6 kA/10 kA), coordination with MCB/MCCB, cable sizing & torque, environment, and periodic TESTs. By following the RKN/RKN-b Instruction Manual—wiring diagrams, 4-pole-as-2-pole method, TEST routine, cautions, and dimensions—you’ll deliver a system that is safe for people, stable in operation, and compliant with IEC 61008-1. [RCCB] 사용설명서_Manual_EN_202502

Contact LS ELECTRIC Vietnam
For technical consultation & pricing on RCCB solutions: Hotline 18006870 | Email: hamh@ls-electric.com.vn

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