6kA MCB – 40A 1 Pole B Curve (WMC140B)

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.

• 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

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.

• 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 Z_s values meet BS 7671 limits
• Consider C-curve for inrush-sensitive loads (motors, compressors)
• Tighten terminals to manufacturer torque values and record results

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.