Regulation 421.1.201

AMK said:

If a plastic consumer unit is selected for a detached garage (separate from the main property), would it be necessary to document the reasoning on the Electrical Installation Certificate ? For instance, considerations such as minimal fire risk and budget constraints may justify this choice.

Perhaps ... but would anything need to be documented if it's not a 'departure' ?

This guidance indicates perhaps not a departure for a detached outbuilding: https://www.electricalsafetyfirst.org.uk/professional-resources/technical-e-news/consumer-unit-mythbuster/

BUT

If you take the words as written in Regulation 421.1.6 BS 7671:2018+A2:2022+A3:2024 at face value, then:

1. Domestic (household) premises is, to the best of my knowledge, a clearly defined term that includes the house, outbuildings and the entire curtilage of the 'premises'.
   
   
2. 'within' does not have to mean 'indoors', it can mean (and would make most sense to mean, given 1. above), 'within the curtilage of the premises'.

Now, I'm not going to provide a specific opinion ... I can clearly see there are differing views on this, and the answer may well change with changing circumstances.

I would point readers of this thread to the advice given in Clause 4.2.3 of BS 0:2021, that interpretation of the standard is the responsibility of the user of the standard, and only a court of law can give a definitive interpretation.

gkenyon said:

'within' does not have to mean 'indoors', it can mean (and would make most sense to mean, given 1. above), 'within the curtilage of the premises'.

Exactly! One might say, for example, that the Bank of England lies within the City of London.

To me "Domestic premises" would be a clearly defined term that includes the house, outbuildings and the entire curtilage of the 'premises' - it's the "(household)" qualification that doesn't quite fit into that. Household is generally used to refer to people - so where people usually reside (the main house, and any habitable outbuildings - e.g. a detached granny flat) would seem to count, but other buildings where people don't usually live (as in eat, sleep, not just pass through like they would a shop or a railway station) could be seen as excluded. At least that's one interpretation that does fit in with the published guidance. Maybe next time the reg itself can be re-worded to make things clearer.

   - Andy.

AJJewsbury said:

but other buildings where people don't usually live (as in eat, sleep, not just pass through like they would a shop or a railway station) could be seen as excluded.

But ... the word 'premises' doesn't support that view ... it's not an easy one, is it?

The issue being, that there are already legal judgements made as to what some of these terms are, so whilst we can discuss this at length, and try to put individual spin on terms either in isolation, or in conjunction with other words or terms, the legal process will have the last say.