I have a situation in which the floor corridor circuit breaker trips before my home one. The corridor one is what appears to be a D20, so type D, 20 A.

corridor breaker

The flat breaker is what appears to be a type A, 25 A, but I could have researched that wrong.

flat breaker

From what I researched, D Types are supposed to be used for heavy industrial use, and are supposed to trip for 10-20x the power while A-types are supposed to be no more than 2 times?

Other point which is surprising is that I don't know how I would generate 230*20*10 = 46 kW at home. From my experience, it has been tripping in cases in which I have an oven, stove and kettle running on top of the baseline, so something around 8.5-10 kW tops.

So I wonder what is going on and if I read those labels correctly. And on top of that, I worry there is something wrong in the installation that would cause a surge big enough to make the D20 trip.

  • Then why put a continuous rating of 20A on the circuit breaker? You may get a higher current for shorter periods of time but thermal trip will trip from sustained over current. You cannot get more out than is meant to come in. Commented Sep 18, 2023 at 13:54
  • @StainlessSteelRat I realise I was not clear in the first place, the corridor one is external, it comes between the flat and the power meter, so I have no hand on it. I also realise I do not understand fully how a D-type works. Ultimately it will trip from being just over 20? I could not find this information.
    – Gnoupi
    Commented Sep 18, 2023 at 15:29
  • Clarify please - the 20A floor breaker is for only one circuit in the flat and the flat "breaker" is 25A and is in front of all the circuits in the flat ?
    – Criggie
    Commented Sep 19, 2023 at 18:41

3 Answers 3


The CFI6-25/2/003 is an RCCB - Residual Current Circuit Breaker (also known as an RCD or a GFCI). It will not trip if you exceed the 25A rating - that's only the maximum current it is intended to handle. There should be another breaker nearby that limits the current.

  • eaton.com/au/en-gb/products/… "A residual current circuit breaker must be used in conjunction with a miniature circuit breaker (MCB)."
    – david
    Commented Sep 19, 2023 at 1:01
  • This should be the accepted answer.
    – nobody
    Commented Sep 19, 2023 at 1:31
  • Only after adding my answer did I realize GFCI and RCDBs are the same... perhaps see of you can add the word GFCI somewhere in your answer, I feel like more people are familiar with that than with RCDBs? Me, for one... Commented Sep 19, 2023 at 5:58
  • As far as I'm aware MCB is meant to trip when here's too much current flowing probably so much current is drawn as a result of short circuit or simply load is high .. I mean AC , water heater,Iron box etc. all are on the run and circuit is drawing much power and it trips.. RCD is when when some gets electrocuted.. it detects the incoming and outgoing current is not same so it trips... GFCI is meant for Groud Fault related things.. both are not same
    – Amogam
    Commented Oct 3, 2023 at 12:21

10kW / 240V = 41.67A.

You are overloading both circuit breakers. A 20A industrial breaker may allow greater peak currents (like, a giant motor starting up) than a 25A residential breaker, but is still going to trip sooner on greater sustained currents.

  • Ah, I realize I misread the tripping charts for those: external-content.duckduckgo.com/iu/… I took into account only the magnetic part, not the thermal one. (first time I see a chart with the separation, other info only highlighted the magnetic part)
    – Gnoupi
    Commented Sep 18, 2023 at 15:31
  • 1
    This is wrong. “overloading both circuit breakers” is not true - the CFI6 is only a RCB/GFCI. It does not monitor total current, only leakage.
    – nobody
    Commented Sep 19, 2023 at 1:33
  • @nobody The wires do not monitor total current either, but they are also overloaded. Commented Sep 19, 2023 at 2:00
  • 3
    I’m not sure what your point is. The OP is asking “why is the D20 tripping before the CFI6 on overcurrent, when I believe the CFI6 is more sensitive to overcurrent”. The proper answer is “the CFI6 does not monitor for overcurrent (only leakage) so of course it’s not tripping on overcurrent”. It’s not a matter of different curves. Yes 41A is more than the CFI6-25 should see but it won’t cause a trip, only danger.
    – nobody
    Commented Sep 19, 2023 at 2:09

It's basically a GFCI, not a breaker. They can almost always be identified by the test button, I've never seen one without it, nor a breaker with one.

Exceeding the current will kill it in non-guaranteed ways, including fire, short-circuit, or alien invasions. It's not meant to trip on overload, but on any connection between live and ground.

Please use the test button asap. If it does not trip when using the test button, get it replaced. The current limiter should have saved it, but it's better to be sure.


  • This is just duplicating SimonB's answer.
    – nobody
    Commented Sep 19, 2023 at 12:25
  • 1
    I see, it’s not meant to break on overload but on short-circuit or leakage. Different use indeed. I’ll be checking that test button as soon as I can get everyone to turn off their PCs :) thanks for the safety advice
    – Gnoupi
    Commented Sep 19, 2023 at 17:32
  • @nobody if you read my comment on that answer you'll understand why... He had not yet edited it to mention GFCI, and I did not know what RCB meant. So no, if you check the timestamps and edits, it's not. Commented Sep 19, 2023 at 20:24

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