Isolation for 3 phase domestic installations

[Ian1981]

4 pole isolation for domestic 3 phase installation.
Is it a requirement?
Regulation 537.1.4 requires a linked switch or circuit breaker to isolate both live conductors of a single phase supply for ordinary persons of a household or similar installation.

 

[Risteard]

LOL. Not trying to be rude.

But it's clear that they have deliberately differentiated between single and three-phase installations. There's absolutely no reason to believe that this wasn't intended as they have gone to the trouble to make this differentiation.

 

[davesparks]

Dave read the regulation it’s specifically mentions household and similar installations as an example as in a main switch intended for operation by ordinary persons.
But I understand what you are saying regarding the fact it only implies single phase and not 3 phase.

It doesn’t ‘imply’ single phase, it states categorically single phase.

Read exactly what is written in plain English, not what you want to see.

 

[Ian1981]

Imply was a poor choice of word on my part it does indeed categorically say single phase.
Just to note I did not once say it was a requirement, I simply asked people’s thoughts.
Should have expected the arrogant response I guess Dave.

 

[polo1]

I’m inclined to think that 537.1.4 was written with the presumption that in domestic premises, the supply will typically be single phase.
Where there is a three phase supply in domestic premises, I always provide 4 pole isolation to meet the spirit of this Reg.
I understand that in some parts of the UK, new build domestic properties are being provided with three phase supplies as standard.

 

[Risteard]

I’m inclined to think that 537.1.4 was written with the presumption that in domestic premises, the supply will typically be single phase.
Where there is a three phase supply in domestic premises, I always provide 4 pole isolation to meet the spirit of this Reg.

But they have deliberately distinguished between single phase and polyphase for domestic installations. They could easily have simply written that domestic installations require it - clearly they did not intend this. So to suggest that a four pole isolator is within the "spirit of the Regulation" is frankly an incorrect conclusion to draw.

It's not really that surprising either, as it should be remembered that breaking the neutral in a polyphase installation is not without risk.

 

[Ian1981]

The Supplier will probably supply a 4 pole isolation after their metering anyway for the contractor to connect the tails to.
Perhaps not to be used by the user of the installation but it will be there all the same perhaps?
I do agree that it’s not a requirement in TPN installations which are not TT
Regulations 537.1.2 and 537.2.1.1 are the ones to note.

 

[johnduffell]

I always assumed the single phase two pole main isolation stipulation is in case the polarity is incorrect at the meter tails. This can go unnoticed indefinitely, whereas you'd do well to leave 3p with a neutral/live reverse and not get called back soon. Although if there is no three phase equipment it's possible, but unlikely due to the lack of 3p domestic installs.

The risk with 3p is the same one you'd have regardless with the integrity of the equipotential zone.