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Chapter 41: automatic disconnection, final and distribution circuits0.4 seconds or 5 seconds. Which applies?

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Chapter 41 and automatic disconnection

Part 4 is where the exam weight is, and Chapter 41 is the biggest chapter in it — big enough to have its own contents page. Open Part 4 and you get an intro, a scope, then Chapter 41: protection against electric shock.

§Section 410 — protective measures shall consist of independent provision.

The main sections of Chapter 41, in book order:

SectionCovers
411Automatic disconnection of supply (ADS) — the big one
412Double or reinforced insulation
413Electrical separation
414Extra-low voltage (SELV and PELV)
416Provisions for basic protection

Inside 411 sits the regulation this whole part revolves around:

§411.3.2 — automatic disconnection in case of a fault. A protective device shall automatically interrupt the supply to the line conductor of a circuit or equipment in the event of a fault.
✋That's the device providing automatic disconnection for that circuit. Normally it is the circuit's overcurrent protective device (a circuit breaker, a fuse or an RCBO), or an RCD where it gives the fault protection, as on a TT system.

Chapter 41 · protection against electric shock (own contents page) Section 410 · independent provision 411.3.2 · automatic disconnection in case of fault

Final circuits vs distribution circuits

Before the tables make sense you need this distinction, because the whole of Table 41.1 hangs on it — and it's not about rings versus radials.

Main board Sub board Socket distribution circuit board to board · 5 s (TN) final circuit board to outlet · 0.4 s (TN) supply
The cable between two boards is a distribution circuit. The cable from a board to the thing the user plugs into is a final circuit. Every circuit you install is one or the other.
FFinal circuit
Consumer unit → outlet. The circuits the person you hand the installation to actually uses. Sockets, lights, cooker, shower.
DDistribution circuit
Board to board. Main board to a garage sub-board; the supply from the transformer into the main board.
Quick identification in an exam question. 0.4 s → a final circuit within 411.3.2.2 (≤ 63 A with sockets, ≤ 32 A fixed equipment). 5 s → a distribution circuit, or a final circuit over 63 A with sockets or over 32 A fixed equipment (411.3.2.3).

Part 2 · definitions of final circuit and distribution circuit

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