Sparkingchip said:

That is why I still frequently read the discussions on this forum, in amongst other sources of information and it would actually be really helpful if the discussions on this forum had the exact date on them when things were said and people could actually add a note saying that due to changes in the requirements what was a correct answer in April last year changed in May last year, so is no longer correct.

Agreed - it's the simple principle, though, of "when should and when should I not ignore changes in an existing installation".

After all, extending a lighting circuit to add a smoke detector/alarm (that did not at the time have surge protection to latest standard) is, at its core, a very similar discussion to extending a circuit to add a socket-outlet (which doesn't have ADS according to BS 7671 for protection against electric shock).

Fundamentally, both potentially affect life-saving issues, both are non-conformances, and a decision must be taken by the designer/installer

Having a look an an example of this type of plug in MCB which are available brand new from electrical wholesalers as well as preused through EBay and other websites, it’s very debatable how they should be isolated and locked off, as someone could quite easily unplug a MCB with the toggle locked off and swap it for another device in the same board.

So I am not convinced the Electrical Safety First Best Practice Guide Two actually shows the best practice.

I’m only throwing in a comment, not stating what I think is best practice, but I think these particular devices need treating as fuses and should be pulled from the board, but what then?

I can’t see a readily available lock offs for what is a BS3036 15 amp fuse holder on any websites.

www.ebay.co.uk/.../133743674126

Agreed, when the BS 3036-type boards were designed, the EAWR wasn't in place, and there was a different view of "safe working" in LV installations.

Under CDM Regulations (which also weren't in place back then) the designer now has a duty to ensure safety for those working on the electrical installation in future (this duty applying to all electrical installations, including domestic).

A personal opinion.

The older I get the more risk averse I get, so with plug in MCBs  and fuses I generally turned the whole installation off, remove the fuse board cover, then disconnect the circuit and park the circuit conductors in the earth bar, put the fuse board cover back on and reenergise the rest of the installation.

If the conductors won’t reach the earth bar use a fly lead and connector.

It may seem over the top, but I have had idiots trying to turn circuits back on whilst I have been working on them.

"Extending a circuit" seems to be difficult with an empty spare device in the MCB, but I entirely agree that it is the new work which should comply.

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.

The selection of the circuit-breaker to provide ADS for the addition to the circuit is included in the certificate, surely?

Well, would you refuse to add an extra socket to an existing circuit, because it was protected by a BS 3871 MCB? I'd suggest that the requirement for existing kit is only that it is "adequate" to feed the alteration, rather than complying with every dot and comma of the current regulations. So far, I don't see the old devices undermining the safety of ADS itself - the blowing of a fuse isn't required to provide 3mm separation, so the isolation requirement is for maintenance rather than ADS per se, it would seem. If isolation may be provided by other means, it could be said that the existing is adequate, if not 100% to current standards.

   - Andy.

AJJewsbury said:

If isolation may be provided by other means,

It's making an assumption about the intent of 531.1.1, but I follow the logic.

However, as discussed above, the older isolators likely to be present were made to very similar requirements, and tested to 2 kV only.

From my perspective, given the industry guidance, and taking that at face value knowing what's in the older standards vs the current ones, I'm having to say "I don't know".