Scope, Fundamental Principles and Definitions
What the rules cover
ET10101 is the national wiring rules for fixed installations. Its scope runs from the point of supply (origin of the installation) through final circuits to the points of use, and it applies to new work, alterations and additions. It does not cover supply-authority equipment upstream of the origin, nor appliances themselves - though the fixed wiring feeding them is in scope. A frequent trap is a question asking whether a given item (a plug-in appliance, a supplier's fuse, a telecommunication cable) falls within the rules; read the scope clause carefully rather than assuming.
Fundamental principles
Five principles underpin every clause and are examinable in their own right: protection for safety; design so the installation functions for its intended use; protection against external influences; economy of design; and sustainability/documentation. Where a specific rule is silent, you reason from these principles.
Definitions that decide questions
The definitions clause is where marks are won and lost. Know precisely:
- Origin: the point where supply is delivered to the installation.
- Nominal voltage vs rated voltage.
- Live part vs exposed conductive part (metalwork that can become live under fault, normally not live) vs extraneous conductive part (metalwork not part of the electrical installation that may introduce a potential, e.g. a metal water pipe).
- Basic protection (insulation, barriers) vs fault protection (earthing, automatic disconnection).
- Isolation (for safety/work) vs switching (functional).
Worked rule of thumb
The exposed/extraneous distinction drives bonding decisions: a metal pipe entering the building that is reliably connected to earth elsewhere is extraneous and needs main protective bonding; a metal sink fed by plastic pipework may not be. Test by asking "is it part of the electrical installation?" and "can it introduce a potential?"