High-current MCBs (63A–125A) are used on circuits that feed large loads, sub-mains, commercial equipment or three-phase machinery. Choosing the right one comes down to breaking capacity, curve type, pole configuration and the load behaviour of the equipment you're protecting.
Quick Answer: Choose a high-current MCB based on current rating, curve type (B, C or D), fault level (6kA vs 10kA), and pole count (1-pole for single-phase, 3-pole or 4-pole for three-phase). Heavy-load circuits such as heat pumps, compressors, distribution sub-mains and industrial machinery will typically require C or D Curve devices at 63A or above.
Browse the full heavy-load range: High-Current MCBs (63A–125A)
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What Makes a High-Current MCB Different?
High-current MCBs are designed for circuits where both load and fault levels exceed domestic values. They use larger internal components, higher magnetic trip thresholds and stronger contact assemblies to deliver reliable protection on heavy-load circuits.
They offer:
- Higher continuous load capacity (63A–125A)
- Higher fault-breaking abilities (6kA or 10kA)
- Curve types suited to inductive/motor loads
- Single-pole, 3-pole and 4-pole configurations
Key Factors When Choosing a High-Current MCB
Heavy-load circuits demand the correct MCB selection across four main areas:
1. Current Rating: 63A, 80A, 100A or 125A
The device must match both the load and cable capacity while meeting disconnection times under BS 7671. Oversizing leads to poor protection; undersizing leads to nuisance tripping.
2. Curve Type: B, C or D
- B Curve: Low inrush circuits
- C Curve: Medium/high inrush, motors, pumps
- D Curve: Very high inrush, industrial machinery
3. Fault Level: 6kA vs 10kA
Higher fault levels typically require 10kA devices - especially closer to the supply transformer or inside commercial boards.
4. Pole Count: 1P, 3P or 4P
- 1-pole: Heavy single-phase loads
- 3-pole: Three-phase motors and equipment
- 4-pole: Three-phase + neutral disconnection
Common Heavy-Load Applications
High-current MCBs are used anywhere the installation draws substantial current, experiences high inrush, or forms part of a distribution chain.
Typical use cases:
- Heat pumps and large HVAC units
- Commercial kitchen equipment (ovens, fryers, induction banks)
- Workshop machinery (lathes, saws, compressors)
- Distribution sub-mains feeding secondary boards
- Industrial motors and conveyors
- Large water pumps and booster sets
- UPS systems and server racks
Installer-Favourite High-Current MCBs
These high-capacity devices are widely used across commercial, industrial and heavy-load domestic installs.
- 63A 6kA MCB – 1 Pole B Curve
- 63A 6kA MCB – 1 Pole C Curve
- 100A 3-Pole Auto-Resetting MCB
- 63A 3-Pole 10kA MCB – C Curve
- 63A 3-Pole 10kA MCB – B Curve
- 63A 4-Pole 10kA MCB – D Curve
- 63A 4-Pole 10kA MCB – C Curve
- 63A 4-Pole 10kA MCB – B Curve
- 100A 4-Pole 10kA MCB – C Curve
- 63A 1-Pole 10kA MCB – C Curve
- 63A 1-Pole 10kA MCB – B Curve
Browse the full heavy-load category: High-Current MCBs (63A–125A)
FAQs
Choosing the correct high-current MCB can be confusing, especially around curve type, fault level and three-phase requirements. These FAQs clarify the essentials.
Do high-current MCBs need to be 10kA?
Often, yes. Many commercial boards and transformer-fed circuits require 10kA breaking capacity.
Should heavy-load circuits use C or D Curve?
C Curve works for most motor-driven loads. D Curve is best for very high-inrush industrial equipment.
Do 63A+ circuits require RCBOs instead?
Not necessarily. RCBOs at high ratings exist but are less common. Many systems use upstream RCD protection with a high-current MCB.
When do I need a 3-pole or 4-pole MCB?
Three-phase circuits require 3-pole (phase only) or 4-pole (phase + neutral) depending on whether neutral switching is required.
👉 Need reliable protection for heavy-load or commercial circuits? Shop all High-Current MCBs