B Curve MCBs for Standard Domestic Circuits
B Curve MCBs are miniature circuit breakers designed for circuits with low inrush currents and predictable load behaviour. They are the default choice for most domestic and light commercial installations, providing fast overcurrent and short-circuit protection for lighting, socket and general-purpose circuits.
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B curve devices trip between three and five times their rated current, giving them a quick response to faults while remaining stable under normal operating conditions. They are available across a full spread of current ratings and breaking capacities, allowing installers to match protection to both the supply fault level and the connected load.
- B curve tripping characteristics for low-inrush circuits
- Ideal for lighting and socket circuits in homes and small workplaces
- Available in multiple ratings from 6A upwards
- 6kA and 10kA options to suit different fault levels
- Single-module DIN-rail format for fast installation and replacement
B Curve MCBs are widely used in new builds, rewires and consumer unit upgrades where the prospective fault current and load profile fall within standard domestic ranges.
6kA MCB – 40A 1 Pole B Curve (WMC140B)
£1.84
£2.99
The WMC140B is a 40 A single-pole 6 kA Miniature Circuit Breaker (MCB) built for high-load domestic and light-commercial circuits such as sub-mains, electric heaters and distribution feeds. Its B-curve tripping profile (3–5 × In) delivers fast, reliable protection against overcurrent and short-circuit faults while...
6kA MCB – 20A 1 Pole B Curve (WMC120B)
£1.84
£2.99
The WMC120B is a robust 20 A single-pole 6 kA Miniature Circuit Breaker (MCB) providing accurate overcurrent and short-circuit protection for socket and radial circuits in homes, garages and light-commercial buildings. It features a B-curve tripping profile that operates at 3–5 × rated current to...
6kA MCB – 16A 1 Pole B Curve (WMC116B)
£1.84
£2.99
The WMC116B is a 16 A single-pole 6 kA Miniature Circuit Breaker (MCB) designed for socket and small-power radial circuits. It combines dependable overcurrent and short-circuit protection with a B-curve tripping characteristic that responds at 3–5 × rated current — ideal for domestic and light-commercial...
6A 4 Pole 10kA MCB C Curve – WKC406C
£14.16
The WKC406C is a 6A 4 pole 10kA Miniature Circuit Breaker (MCB) designed for three-phase + neutral protection. With its C Curve trip characteristic, it is suited to inductive load circuits such as motors, HVAC, and commercial distribution boards in three-phase systems, EV charging units,...
63A 4 Pole 10kA MCB B Curve – WKC463B
£14.16
The WKC463B is a 63A 4 pole 10kA Miniature Circuit Breaker (MCB) designed for three-phase + neutral protection. With its B Curve trip characteristic, it is best suited to resistive load applications such as large socket outlet groups, small power distribution panels, and lighting circuits...
What Is a B Curve MCB?
A B curve MCB is a miniature circuit breaker that trips when the current reaches between three and five times its rated value. This makes it ideal for circuits with low starting currents, where any significant spike is likely to be a genuine fault rather than normal operation.
Where B Curve MCBs Are Used
- General lighting circuits including LED and mixed loads
- Socket and ring main circuits in homes and small offices
- Immersion heaters and other resistive loads
- Small appliance circuits with predictable current draw
- Standard domestic distribution boards where inrush current is low
Why Choose a B Curve Over C Curve?
B curve devices are more sensitive to overcurrent than C curve breakers. This is beneficial on circuits that do not experience high start-up currents, as it ensures faults are cleared quickly while minimising the risk of wiring damage.
- Faster response to overcurrent on low-inrush circuits
- Correct matching to typical domestic load profiles
- Helps protect cable insulation by limiting fault energy
Breaking Capacity & Compliance
B Curve MCBs are available with different breaking capacities, commonly 6kA for standard domestic installations and 10kA for higher fault-level environments. All devices are designed to comply with BS EN 60898 and support 18th Edition Wiring Regulations when correctly selected.
Selecting the Right Rating
The correct rating depends on cable size, installation method and expected load. Typical domestic choices include 6A and 10A for lighting, 16A or 20A for radial circuits, and 32A for ring mains or heavier loads.
Installer Benefits
B Curve MCBs provide dependable, predictable protection across everyday circuits. With a wide range of ratings and breaking capacities, they allow electricians to design safe, compliant boards that match real-world domestic and light commercial installations.