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Each of the two devices with yellow test buttons are marked '63A'. My assumptions:

  • The set of devices to the left of each of these are connected to them
  • The markings on each device in the form BNN denote rated current, e.g. B6 is 6 Amps.

The right-hand bank of devices goes 6 + 32 + 40 = 78A, which is clearly greater than 63A.

Furthermore, the sum of all the rated currents is 132A, which is clearly greater than the rated current on the main switch of 100A

1) Is this how the markings and the layout of this consumer unit are meant to be interpreted?

2) Is this a problem?

  • You mention below that your lawnmower and iron trip breakers when you are using them. How much current do those devices draw? – longneck Aug 19 '15 at 20:15
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1) Yes, your interpretation of the layout and markings seems to be correct.

2) No, it's not a problem, it's a very typical setup. You can have breakers totalling more than the total capacity of the unit, on the ground that you are unlikely to be running each circuit at or near capacity at the same time.

A MCB (or RCD, fuse, etc) is designed (and sized) to protect "downstream" of it, not those "upstream". Ie the 6A breaker on the left of the consumer unit above is there to protect the 1mm^2 or 1.5mm^2 cable that is connected into it, as those cables can safely handle a 6A load. They aren't there to protect devices further upstream.

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