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Disconnection times: Table 41.1Does every socket in a house need an RCD?

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411.3.2 sends you to Table 41.1, which gives the maximum disconnection times for final circuits. Its scope is 411.3.2.2 (p.71): final circuits not exceeding 63 A with one or more socket-outlets, and not exceeding 32 A supplying only fixed equipment. Read the column headings carefully — there are two halves and people pick the wrong one.

System50 V < U₀ ≤ 120 V120 V < U₀ ≤ 230 V
TN (AC)0.8 s0.4 s
TT (AC)0.3 s0.2 s
✋The heading uses the ≤ symbol — "less than or equal to". The UK's nominal U₀ is 230 V, which sits at the top of the 120 V < U₀ ≤ 230 V band, not in the one above it. Also check whether the question says AC or DC: the table has separate rows and the DC times are longer.

The table is for final circuits within 411.3.2.2. Distribution circuits, and final circuits outside 411.3.2.2, are handled by the regulations printed underneath the table:

CircuitTNTT
Final, within 411.3.2.2 (230 V AC)0.4 s0.2 s
Distribution, or a final circuit over 63 A with sockets / over 32 A fixed equipment5 s1 s
!Highlight the words "final circuits" in the regulation above the table, and the two distribution-circuit regulations below it. That pair of highlights answers a lot of questions on its own.

411.3.3 — socket outlets and additional protection

Sitting just below: 411.3.3, additional requirements for socket outlets and for mobile equipment used outdoors. Socket-outlets with a rated current not exceeding 32 A, and mobile equipment not exceeding 32 A used outdoors, require additional protection by a 30 mA RCD. It is not limited to homes: it covers sockets liable to be used by ordinary persons, sockets in other locations, and mobile equipment outdoors. The only exception is for sockets in other locations, and it needs a documented risk assessment by a skilled person. The regulation that is limited to domestic (household) premises is 411.3.4, for circuits supplying luminaires.

✋Read the exception carefully. It applies only to socket-outlets in other locations, and only with a documented risk assessment by a skilled person. Socket-outlets up to 32 A liable to be used by ordinary persons have no exception.
Why that matters on site. An example: a workshop where test bays were wired through a single RCD, so every insulation-resistance test killed the power to the whole room and someone had to reset the RCD. The fix that meets the regulation without the nuisance: fit RCD socket outlets at the points that need them, rather than putting the whole circuit behind one RCD. Good selectivity is a design decision.

Table 41.1 · maximum disconnection times, final circuits 411.3.2.2 · p.71 · Table 41.1 scope: ≤ 63 A with sockets, ≤ 32 A fixed equipment 411.3.2.3 · p.72 · distribution circuits 5 s (TN) 411.3.2.4 · distribution circuits 1 s (TT) 411.3.3 · p.72 · socket outlets and outdoor mobile equipment ≤ 32 A, 30 mA additional protection

Table 41.1 — maximum disconnection times, FINAL circuits 50 V < U₀ ≤ 120 V 120 V < U₀ ≤ 230 V TN (AC) 0.8 s 0.4 s TT (AC) 0.3 s 0.2 s ✋ The heading says ≤ — less than or equal to. The UK’s 230 V sits at the top of the second band, not in the first.
Two halves, and people pick the wrong one. Read the column heading before you read the number.

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