I'd say it depends on the situation. BS 7671 allows isolation to be remote, provided it can be locked off. However using the MCCB as an isolator would only be sensible if the circumstances were right  - e.g. would everyone who might need to isolate the equipment have access to the DB? Would giving everyone access to all the circuits be sensible (what if they threw the wrong breaker by mistake - would it cause a lot of trouble?). How often would isolation be required? MCCBs normally aren't intended for frequent operation. It's one of those things where the electrical design is driven as much by the wider situation and customer requirements as purely electrical considerations.

Usually no need for 4-pole, on TN systems, the N generally doesn't need to be isolated (there might be exceptions though).

  - Andy.

Isolation would be required by competent people that would have access. Clear labelling would be provided to ensure the wrong switch wasn’t tripped. Isolation would be required for periodic maintenance only. Thanks

Electron666 said:

Isolation would be required for periodic maintenance only.

That is far too woolly. The bottom line is the Health and Safety at Work etc. Act 1974.

Periodic maintenance could be replacement of electrical parts by an electrically qualified person, or replacement of mechanical parts by a non-electrically qualified person, or cleaning by an unqualified person, etc.

I do not think that BS 7671 provides the answer. What is required, beyond doubt, is a safe system of working.

Chris Pearson said:

I do not think that BS 7671 provides the answer.

Agreed, BS 7671 cannot provide the answer, because as you say, it depends on who needs the isolation and why.

Chris Pearson said:

I do not think that BS 7671 provides the answer.

Agreed, BS 7671 cannot provide the answer, because as you say, it depends on who needs the isolation and why.