Description
Four Pole MCB 80A — SCB8-125 4P 400VAC Three Phase Circuit Breaker
The Four Pole MCB 80A (model SCB8-125) is a high-current, large-frame miniature circuit breaker built for three-phase electrical systems. With four switched poles, it simultaneously disconnects all three line conductors and the neutral, giving you complete isolation of a three-phase circuit in one mechanical action. Rated at 80 amps continuous and tested to 400V AC, this breaker is the standard choice for the main incomer of medium commercial premises, three-phase solar inverter outputs, large workshop sub-mains, and three-phase pump and motor feeds across Kenya.
The SCB8-125 family covers the upper MCB range from 80A to 125A, sitting at the bridge between domestic miniature breakers and full moulded-case devices. Its 125A frame size gives it the mechanical strength and arc-quenching volume that smaller MCBs lack, while still mounting on the same 35mm DIN rail used in every Kenyan distribution board.
What this breaker is built for
- Three-phase main incomer: Acts as the primary disconnection point for a workshop, retail unit, small factory, or office block fed from the national grid.
- Large solar AC output: Protects the AC side of three-phase hybrid and grid-tie inverters between 15 kW and 50 kW.
- Industrial motor feeders: Branch protection for three-phase pumps, compressors, lifts, and HVAC plant rooms.
- Three-phase distribution boards: Used as the upstream breaker before a three-phase sub-distribution board with single-phase outgoing ways.
- Backup and changeover panels: Switches between a three-phase generator, a solar hybrid source, and the national grid feed.
Why four poles instead of three?
A 3P breaker switches only the three line conductors. The neutral stays permanently connected. For most balanced three-phase loads — three-phase motors, balanced inverter outputs, evenly distributed sub-boards — a 3P device is enough. However, where the load may be unbalanced, where you have single-phase outgoing ways from a three-phase distribution board, or where the system uses TT or IT earthing, the neutral conductor can carry significant fault current. A 4P breaker disconnects that neutral along with the three phases, which is the safer and increasingly required configuration for solar AC output panels, healthcare premises, and any installation where complete galvanic isolation is needed for safe service work.
Technical Specifications
| Specification | Value |
|---|---|
| Model Number | SCB8-125 |
| Number of Poles | 4P (Three Phase + Neutral) |
| Rated Current (In) | 80A |
| Frame Size | 125A |
| Rated Voltage (Ue) | 400V AC three-phase |
| Rated Frequency | 50 / 60 Hz |
| Trip Curve | C-curve (5–10 × In) |
| Trip Mechanism | Thermal-magnetic |
| Rated Breaking Capacity (Icn) | 10 kA |
| Insulation Voltage (Ui) | 690V |
| Pollution Degree | 2 |
| Mechanical Life | 15,000 operations |
| Electrical Life | 3,000 operations |
| Mounting | 35mm DIN rail (clip-on) |
| Terminal Capacity | Up to 50mm² cable |
| Operating Temperature | -5°C to +45°C |
| Indicator | Trip-free position window per pole |
| Standard Compliance | IEC 60898-1 / IEC 60947-2 |
| Application Type | AC three-phase distribution |
Key Features
- Full four-pole switching — three lines plus neutral break together, giving total circuit isolation for safe maintenance.
- 10 kA breaking capacity — higher than standard 6 kA domestic breakers, matched to the heavier fault currents seen at incomer positions.
- Common trip mechanism — a fault on any single pole trips all four together, preventing partial isolation under fault.
- C-curve thermal-magnetic trip — handles three-phase motor startup, transformer inrush, and inverter capacitor charge without nuisance operation.
- Large terminal capacity — accepts cables up to 50mm² for the heavier conductor sizes used at 80A loads.
- DIN-rail clip mount — installs into any standard distribution panel without modification, saving installation time.
- Flame-retardant moulded housing — handles repeated fault clearance without softening or deforming.
- Per-pole status windows — confirms every conductor is mechanically open before any downstream work begins.
Typical Applications in Kenya
- Main incoming switch for offices, retail outlets, salons, and SME workshops on a three-phase feed
- AC output protection for large three-phase hybrid solar inverters (15 kW to 50 kW range)
- Sub-main feeders to remote outbuildings on a farm, agricultural processing shed, or rural school
- Three-phase borehole and irrigation pumps
- Welding plant, CNC machinery, and three-phase compressors in workshops
- HVAC and chiller plant rooms in hotels and clinics
- Backup and ATS panels switching between solar, generator, and grid
- Three-phase EV charging point isolators
Installation Notes
The SCB8-125 must be installed by an EPRA-registered electrician. As a four-pole device it requires the three line conductors and the neutral to be terminated in the correct sequence — typically L1, L2, L3, N from left to right on the supply side, with the matching load conductors mirrored on the outgoing terminals. Each pole carries up to 80A continuously, so terminal torque is critical: a loose connection at this current rating heats up rapidly and is a leading cause of distribution-board fires. The breaker should be mounted in a metal-enclosed distribution panel with adequate ventilation, and the panel itself bonded to the building earth conductor. Phase rotation must be confirmed before energising downstream three-phase motors or inverters.
Designing a three-phase solar or commercial system?
Get a free panel-by-panel breaker schedule and inverter sizing — start with our Solar Calculator, or request a full three-phase layout through My Quote and our engineers will specify everything from incomer to final circuit.
