Most UK consumer units use 6kA MCBs as standard - and in many cases, they’re still the correct and fully compliant choice. But as EV chargers, heat pumps and higher-load equipment become more common, installers are seeing situations where 6kA devices are no longer suitable.
Quick Answer: 6kA MCBs are suitable for the majority of domestic installations and low-fault-level boards where the PSCC (prospective short-circuit current) is well below 6kA. They become unsuitable when a board sits close to the supply transformer, feeds large three-phase loads or EV/industrial equipment, or when measured fault levels exceed 6kA - in which case 10kA devices are required.
Start by checking the full range here: 6kA MCBs.
This guide shows where 6kA is still the correct choice - and the scenarios where they should be upgraded.
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Where 6kA MCBs Are the Correct Choice
6kA devices remain fully compliant in the vast majority of domestic and light commercial installations. They’re designed for circuits where the PSCC is comfortably below 6,000A - which covers most residential supply arrangements.
Common situations where 6kA MCBs are perfectly suitable:
- Standard domestic consumer units (typical PSCC 0.5kA–3kA)
- Most new-build homes with modern supply networks
- Outbuilding or garage boards fed by long submains
- Small commercial units far from the transformer
- Domestic EV / heat pump boards where PSCC remains low
In these installations, a 6kA MCB offers all the fault-breaking capacity required under BS 7671.
Where 6kA MCBs Are Not Suitable
6kA devices become unsuitable when the fault current at the board can exceed the breaking capacity. This is more common in commercial and industrial environments.
Situations where 10kA (or higher) MCBs should be used instead:
- Boards close to the supply transformer
- Three-phase distribution boards in commercial buildings
- Warehouse panelboards with short supply cables
- Industrial machinery supplies with high inrush/fault levels
- EV chargers fed from high-fault-level three-phase boards
- Any DB where PSCC tests exceed 6kA
In these cases, moving to a 10kA device is not a “nice to have” - it’s a requirement for safe operation.
See the higher-rated alternatives here: 10kA MCBs.
How Fault Level Determines Whether 6kA Is Enough
The correct choice comes down to a single measurement: PSCC (prospective short-circuit current) at the board.
Typical PSCC readings:
- Domestic boards: 1kA–3kA → 6kA is ideal
- Remote sub-boards: often <1kA → 6kA more than adequate
- Commercial three-phase boards: 4kA–9kA → 10kA often required
- Boards near a transformer: 10kA+ → high breaking capacity essential
Always size the MCB based on the measured or calculated fault current - not just the type of building.
Installer-Favourite 6kA MCBs
Here are some reliable 6kA devices commonly used on domestic and light commercial circuits:
Browse all options here: 6kA MCBs
FAQs
Installers regularly ask these when choosing between 6kA and 10kA devices:
Are 6kA MCBs still compliant in 2025?
Yes - absolutely. They remain the standard domestic choice across the UK as long as the PSCC is below 6kA.
Can I use 6kA MCBs on EV chargers?
Yes, if the EV supply board’s PSCC is low enough. Many domestic EV installs fall well within 6kA limits.
Are 6kA MCBs weaker or lower quality than 10kA?
No - breaking capacity is not a quality rating. It’s simply the device’s tested fault-breaking limit.
Should I just upgrade everything to 10kA?
You can, but it adds unnecessary cost where 6kA is fully compliant and electrically appropriate.
👉 Need reliable protection for domestic or light commercial circuits? Explore all 6kA MCBs