Any technical publication must make sure that its readers are in no doubt about exactly what it says. Thus, the meanings of the terms used must be defined to make them absolutely clear. For this purpose, [Part 2] includes about one hundred and sixty definitions of words used. For example, the term 'low voltage' is often assumed to mean a safe level of potential difference. As far as the Regulations are concerned, a low voltage could be up to 1000 V ac or 1500 V dc!

Important definitions are those for skilled and instructed persons. A skilled person is one with technical knowledge or experience to enable the avoidance of dangers that may be associated with electrical energy dissipation. An instructed person is one who is adequately advised or supervised by skilled persons to enable dangers to be avoided.

An interesting new definition in the 1997 (second) amendments, is one for an ordinary person , who is neither skilled nor instructed. The same amendments also change the circuit categories for segregation of systems (see {6.6.2}). The system voltage is now categorised as Band I, which includes ELV systems for such applications as signalling, bell and alarm installations, and Band II, covering all other voltages normally used for electrical installations, such as our standard 230 V, 400 V systems (which are much more likely in the UK to measure as 240 V, 415V systems).

The reader of the Regulations should always consult [Part 2] if in doubt, or even if he suspects that there could possibly be a different meaning from the one assumed. If the word or phrase concerned is not included in [Part 2], BS 4727.

'Glossary of electrotechnical, power, telecommunication, electronics, lighting and colour terms' should he consulted.