6kA MCB – 40A 1 Pole B Curve (WMC140B)
£1.84
£2.99
18th Ed. Compliant
2-Year Warranty
UK Stock
Free Delivery £30+
Secure Payments With
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 minimising nuisance tripping on steady-load...
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 minimising nuisance tripping on steady-load circuits.
Fully tested to BS EN 60898, this MCB fits all Whitecliffe consumer units and standard DIN-rail enclosures. It offers a 6 kA breaking capacity and a 20 000-cycle mechanical life, making it a dependable choice for domestic and small-commercial distribution applications.
Installer Tip: Ideal for sub-main feeds or heavy fixed loads drawing up to 40 A. Confirm cable size and protective coordination to maintain BS 7671 disconnection times and voltage-drop limits.
- 40 A rated current with B-curve (3–5 × In) tripping
- 6 kA breaking capacity at 230/400 V AC
- Single-pole design – 18 mm module width
- DIN-rail mounted for consumer units and distribution boards
- Complies with BS EN 60898 and BS 7671 (18th Edition A2)
- Tested service life – 20 000 mechanical / 8 000 electrical operations
- Contact position indicator for visual status check
| Part Code | Rating | Curve | Typical Use |
|---|---|---|---|
| WMC132B | 32 A | B | Cookers, heaters and fixed equipment |
| WMC140B | 40 A | B | Sub-mains and high-load feed circuits |
| WMC150B | 50 A | B | Feed circuits and plant equipment |
| WMC140C | 40 A | C | Motors, compressors or loads with higher inrush |
The WMC140B offers robust 6 kA fault protection for high-load radial and sub-main circuits. For installations with motors or transformer inrush, view our C Curve MCB range or use Type A RCBOs for combined overcurrent and earth-fault protection.
Where is a 40 A B Curve MCB used?
Typically on sub-main feeds and high-load radial circuits such as heaters or small distribution boards. B-curve devices provide fast fault clearing at 3–5 × In.
Is the WMC140B compatible with Whitecliffe boards?
Yes – it fits all Whitecliffe consumer units and standard 18 mm DIN-rail enclosures.
Can this breaker be used to feed an outbuilding?
Yes, if the sub-main cable and enclosure meet regulation requirements. Use our IP65 plastic enclosure for outdoor installs.
When should I use a C Curve MCB instead?
Choose a C Curve MCB if your circuit includes motors or equipment with high inrush currents that could trip a B curve device.
What does 6 kA mean?
It’s the breaker’s rated breaking capacity – the maximum fault current it can safely interrupt. For higher fault-level sites, see our 10 kA MCB range.
- Part Code: WMC140B
- Type: Single Pole MCB
- Rated Current (In): 40 A
- Curve: B (3–5 × In tripping characteristic)
- Rated Voltage (Ue): 230/400 V AC
- Rated Frequency: 50/60 Hz
- Breaking Capacity (Icn): 6 kA
- Insulation Voltage (Ui): 500 V
- Impulse Withstand (Uimp): 4 kV
- Dielectric Test Voltage: 2 kV for 1 minute
- Thermal Reference Temp: 30 °C
- Operating Temperature: –5 °C to +40 °C (avg < 35 °C)
- Mechanical Life: 20 000 operations
- Electrical Life: 8 000 operations
- Mounting: 35 mm DIN rail (1 module width)
- Standards: BS EN 60898; BS 7671:2018 (Amendment 2)
- Typical Applications: Sub-mains, distribution feeds and high-load equipment circuits
Install the WMC140B only in a suitable consumer unit or distribution board by a qualified electrician. Confirm the device rating and curve type match the circuit design and upstream protective device.
- Mount securely on DIN rail and verify busbar alignment
- Use B-curve for steady high-load circuits and sub-mains
- Ensure cable size and Zs values meet BS 7671 limits
- Consider C-curve for inrush-sensitive loads (motors, compressors)
- Tighten terminals to manufacturer torque values and record results
