The test report that underpins the DOC will consider the MI's. Often the report will have conditions on approval which are met by specific wording in the test report.

But that report isn't generally put into the public domain - in fact as the test form is typically IECEE copyright the manufacturer couldn't publish it without IECEE permission - which they woudn't get. So yes we have to trust the manufactuer.

If the product has a listing [e.g. UL, TUV, CSA etc.] then it will involve monitoring and re-assessment - and this includes the instructions. But if it's just CE marked [unless there's a notified body] then presume it isn't.

As per 133.5 - If you can produce a robust safety case then you can overide BS 7671. The Scope, Object and Fundamental Principles set out in Part 1 are ultimatly the bit on which the rest of the standard is hung. Overall BS 7671 is not a mandatory standard - but as noted in 114 if you didn't meet BS 7671 then you'd be at a sticy wicket if you found yourself being prosecuted under the Health and Safety at Work Act.

If you had detailed engineering that was properly risk assessed as to why you are deliberatly departing from BS 7671 for a good reason, and noted that report in the departures box on the NIC then you can indeed depart. As an installer you might be installing something innovative which deliberatly departs and which you're advised as such by the manufacturer. Just make sure you note it in the departures box on the IEC. *edit - and obviously only do this if you're satisfied that the departure is underpinned by good engineering advice from a reputable source, not just because the end client has asked you too. Your proefessional and ethical responsibilities must always come first.

The test report that underpins the DOC will consider the MI's. Often the report will have conditions on approval which are met by specific wording in the test report.

But that report isn't generally put into the public domain - in fact as the test form is typically IECEE copyright the manufacturer couldn't publish it without IECEE permission - which they woudn't get. So yes we have to trust the manufactuer.

If the product has a listing [e.g. UL, TUV, CSA etc.] then it will involve monitoring and re-assessment - and this includes the instructions. But if it's just CE marked [unless there's a notified body] then presume it isn't.

As per 133.5 - If you can produce a robust safety case then you can overide BS 7671. The Scope, Object and Fundamental Principles set out in Part 1 are ultimatly the bit on which the rest of the standard is hung. Overall BS 7671 is not a mandatory standard - but as noted in 114 if you didn't meet BS 7671 then you'd be at a sticy wicket if you found yourself being prosecuted under the Health and Safety at Work Act.

If you had detailed engineering that was properly risk assessed as to why you are deliberatly departing from BS 7671 for a good reason, and noted that report in the departures box on the NIC then you can indeed depart. As an installer you might be installing something innovative which deliberatly departs and which you're advised as such by the manufacturer. Just make sure you note it in the departures box on the IEC. *edit - and obviously only do this if you're satisfied that the departure is underpinned by good engineering advice from a reputable source, not just because the end client has asked you too. Your proefessional and ethical responsibilities must always come first.

Keir Stitt  thank you for expanding on the 'due diligence' element.

I've had a few people referring to badly translated MI's as justification. My stock response is to paraphrase my primary school teachers "If the MI's told you do jump of a cliff, would you?".

It's always down to professional judgment - especially if it all goes horribly wrong because at that point you'd need to justify your decision by reference to the paperwork available at the time.

Totally agree if the MI is wrong.  Eg a rose and pedant arrangement for an average bathroom dwelling being unsuitable.  Engineering judgement needs to be applied.

'taking into account' and 'following blindly' are not the same.  I think we have all suffered from translation-ese instructions at some point, and had to stare hard at the sad little pile of bits to work out what they really meant, and then if we really want to do that or something else.
That decision, is the professional judgement that folk pay for of course.

Of course we should refer to the instructions- there may be some essential non-obvious info there - but then use that info with wisdom.

Mike.