Interesting debate, just wondering if there is anything I can do to make it acceptable to use the existing BS3871 device.

Given in this case it's just protecting a sub main. Would it be acceptable to continue using the existing board and add a label stating that MCB's not suitable for isolation, isolation can only be achieved with main switch.

Second question, if the above is not acceptable. how would you feel about doing minor works like adding sockets to one of the other circuits on a BS3871 device or minor works to a circuit connected to another sub board fed by a BS3871 device.

Interesting debate, just wondering if there is anything I can do to make it acceptable to use the existing BS3871 device.

Given in this case it's just protecting a sub main. Would it be acceptable to continue using the existing board and add a label stating that MCB's not suitable for isolation, isolation can only be achieved with main switch.

Second question, if the above is not acceptable. how would you feel about doing minor works like adding sockets to one of the other circuits on a BS3871 device or minor works to a circuit connected to another sub board fed by a BS3871 device.

Alan B said:

Interesting debate, just wondering if there is anything I can do to make it acceptable to use the existing BS3871 device.

It has been an interesting debate.

Do we not always say that the Regs are not retrospective?

Surely modifications, which may not strictly comply with the current Regs may be made to an installation provided that the result is not less safe than the existing situation.

Chris Pearson said:

Surely modifications, which may not strictly comply with the current Regs may be made to an installation provided that the result is not less safe than the existing situation.

Well, the EIC and MEIWC require you to certify that the installation conforms to the stated version of BS 7671. So, Provided you list ALL the departures on the EIC or MEIWC (and have a good reason for them), perhaps?

Is that approach acceptable to everyone? I'm reminded of the following types of discussion:

•  Domestic smoke detection and SPD requirements in line with BS7671 A2 2022 
• https://www.fia.uk.com/news/fia-s-proactive-efforts-lead-to-crucial-amendment-correction.html

This forum has become very flawed and isn’t really fit for purpose.

That post linked to about SPDs and smoke alarms is simply dated as “over a year ago “ without giving an exact date, and as we all know dates are very important when discussing BS7671.

The requirements were different in April and May last year 2023, as the corrigendum was published in May 2023 and it’s now the 26th April 2024.

electrical.theiet.org/.../

The discussion has also been locked, preventing anyone from commenting that the answer I gave then “over a year ago” would be different now and the context will change next week.

Sparkingchip said:

The discussion has also been locked, preventing anyone from commenting that the answer I gave then “over a year ago” would be different now and the context will change next week.

The point being, not what BS 7671 requires NOW, but that:

Chris Pearson said:

Do we not always say that the Regs are not retrospective?

Surely modifications, which may not strictly comply with the current Regs may be made to an installation provided that the result is not less safe than the existing situation.

So, it's OK to ignore current requirements for existing circuits with devices that provide ADS for protection against electric shock, but yet in terms of whether an existing circuit needs an SPD "you MUST follow new requirements" just because the current version of BS 7671 [at the time] says so ???"

I don't follow the logic.

But then again, safety engineering isn't always logic - perceived risk is always a huge factor.

gkenyon said:

Chris Pearson said:

Do we not always say that the Regs are not retrospective?

Surely modifications, which may not strictly comply with the current Regs may be made to an installation provided that the result is not less safe than the existing situation.

So, it's OK to ignore current requirements for existing circuits with devices that provide ADS for protection against electric shock, but yet in terms of whether an existing circuit needs an SPD "you MUST follow new requirements" just because the current version of BS 7671 [at the time] says so ???"

I don't follow the logic.

I do not think that is quite my point - I never mentioned SPDs.

If you can only add or alter a circuit when the whole circuit including the outgoing device is compliant with the the current edition of BS 7671, then any such changes would require that the whole DB, and arguably for consistency, any other upstream DBs would have to be updated. In my view this is disproportionate and unreasonable.

That said, it may be that consideration should be given to replacing the DB with an up to date one as part of planned maintenance.

Broadly speaking, this has been my approach at home where I have BS 3871 MCBs.

Chris Pearson said:

I do not think that is quite my point - I never mentioned SPDs.

Apologies, to be clear it was me who brought that up, because it's the same principle ... potentially an improvement with a "disproportionate" cost required to extend a circuit.