Low insulation resistance reading

[davesparks]

4 pole main switches are fairly common here, but the point was more about the fact we're free to use them, whereas I believe they can not be used in IE.

I wouldn't say free to use, you would only switch the neutral when absolutely necessary.
Switching the neutral introduces a greater risk of losing the neutral to the load whilst the phases are still connected thus damaging the load.

 

[davesparks]

I'd agree where functional switching is concerned, but isolators are manufactured for a specific purpose and to specific standards - there should be no danger of any live conductor 'hanging'.

There is always a non-zero chance of a fault happening.

And why would you need to switch the neutral on a TN supply?

 

[nicebutdim]

There is always a non-zero chance of a fault happening.

And why would you need to switch the neutral on a TN supply?

That's part of the reason why I'm raising this point. I'm under the impression that it isn't permitted in IE, where the vast majority of supplies are TNC-S, but I see plenty of 4 pole isolation on TN supplies in the UK.

I have questions to ask which expand on this and don't wish to hi-jack the OP's thread more than has already happened. It's not a subject I've seen under much discussion on the forum, so have started a thread and would welcome any input.

Isolation of TN supplies.

I haven't seen a lot of discussion on this subject and have questions pertaining to isolation where TN earthing is present and any peculiarites which may exist between TN-S and TNC-S. I see mostly 3 pole main switches on TN earthing systems, but do see quite a few instances where all live...

www.electriciansforums.net

 

[davesparks]

That's part of the reason why I'm raising this point. I'm under the impression that it isn't permitted in IE, where the vast majority of supplies are TNC-S, but I see plenty of 4 pole isolation on TN supplies in the UK.

I have noticed a trend towards installing 4 pole main switches where until a few years ago 3 pole would always have been preferred.

 

[MDJ]

On a TT you need to isolate all conductors including the neutral, hence the switch where the neutral contact is set back so it closes early and breaks late, relative to the 3 phases.

I may have been mistaken regarding TT I will look into that, thank you for the valued reply, but in general I stick to my post, a good topic for us sparks to discuss for sure.