Most domestic boards are full of 6kA MCBs, so when a spec or wholesaler mentions 10kA devices, it’s natural to ask: do I actually need them? The answer comes down to one thing - the prospective short-circuit current (PSCC) at the board you’re protecting.
Quick Answer: You only need a 10kA MCB if the prospective fault current at the point of installation can exceed the breaking capacity of a 6kA device. In practice, that usually means three-phase commercial boards, panelboards close to the transformer, or circuits with high fault levels. Standard domestic boards with lower PSCC are normally fine with 6kA MCBs.
To see all options, start here: 10kA MCBs.
This guide explains what “10kA” actually means, when you must specify it, and which boards and circuits typically require higher breaking capacity.
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What Does 10kA Breaking Capacity Actually Mean?
The “10kA” marking on an MCB is its breaking capacity - the maximum fault current the device can safely interrupt without destroying itself.
In simple terms:
- 6kA MCB - tested to safely break 6,000 amps of fault current
- 10kA MCB - tested to safely break 10,000 amps of fault current
If the prospective short-circuit current at the board is higher than the device rating, the MCB is no longer compliant or safe. It may not be able to interrupt the fault without damage.
Key point: You don’t choose 10kA “for performance” - you choose it when test results or design calculations show that a 6kA device is under-rated at that point in the system.
When Is a 6kA MCB Not Enough?
Whether 6kA is enough depends on how close the board is to the supply transformer and how the installation is arranged.
6kA MCBs are usually fine for:
- Standard domestic consumer units
- Small commercial boards a long way from the supply
- Sub-boards in outbuildings or remote areas
10kA MCBs are typically required when:
- The board is close to the transformer (high fault level)
- You’re working on three-phase commercial or industrial boards
- The PSCC measured at the board approaches or exceeds 6kA
- The specification or consultant design explicitly calls for 10kA
- The board forms part of a panelboard or MCC with high available fault current
Common Use Cases for 10kA MCBs
In practice, 10kA devices show up most often in higher fault-level environments rather than standard houses.
Typical applications include:
- Three-phase distribution boards in commercial buildings
- Panelboards in plant rooms or risers close to the intake
- Industrial machinery supplies with high PSCC
- Warehouse boards with large three-phase loads and short feeds
- EV, lift or large motor supplies when specified
Where fault levels are known to be high, 10kA becomes the default, especially on three-phase D curve devices feeding motors and heavy loads.
For three-phase protection generally, see: Three-Phase Boards & Accessories.
Recommended 10kA MCBs
Here are popular 10kA devices used on three-phase and higher-fault-level circuits:
Browse the full range here: 10kA MCBs
FAQs
Installers often ask these when deciding between 6kA and 10kA devices.
How do I know if I need 10kA?
Measure or calculate the PSCC at the board. If it exceeds the rated breaking capacity of 6kA, you need a higher-rated device such as 10kA.
Can I just fit 10kA everywhere “to be safe”?
You can, but it normally isn’t necessary in standard domestics and may increase cost where 6kA is more than adequate.
Is breaking capacity the same as tripping curve (B, C, D)?
No. Breaking capacity is the maximum fault current the MCB can interrupt. The curve defines how quickly it trips under overloads and short circuits.
Are 10kA MCBs only for three-phase boards?
No - you can use them on single-phase circuits too, but they’re most common where fault levels are highest, which is often on three-phase boards.
👉 Working on a board with high fault levels or three-phase loads? Browse all 10kA MCBs