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Icn and Ics, and why the schedule wants kAWhy does the schedule want kiloamps?
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Guidance Note 3 · 2.6.16. Your Ipf goes on the schedule in kA for one reason: so it can be compared with the figure stamped on the device.
| Marking | What it means |
|---|---|
| Icn | The rated short-circuit capacity, usually in a box on the device — what it can interrupt, though it may be destroyed doing so |
| Ics | The in-service short-circuit capacity — what it can interrupt and still keep working |
Using it
Measured Ipf = 0.6 kA (the greater of PSCC and PEFC) Device = 16 A Type B RCBO, Icn 6 kA 0.6 kA is nowhere near 6 kA -> the device is fine, leave it.
And where it is not fine. The device’s breaking capacity must be at least the prospective fault current where it is installed, so a 6 kA device where the fault current is 7 kA is not suitable on its own. You would need the next rating up — a 10 kA device, same type and rating, different breaking capacity — unless a device on the supply side gives back-up protection (Reg 434.5.1); domestic consumer units carry a conditional rating with the cut-out fuse. Not every brand marks Ics; where it is given, it is stated as a proportion of Icn, so read the device rather than assuming.
Don’t assume a figure. Fault current varies with the supply and the installation. Measure it.
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