3 or 4 Pole main incomer?

[Joenicholson1996]

When ordering a 3 phase + Neutral DB, I forgot to specify that I wanted a 4 pole switch for the main incomer. What came was a 3 pole main switch with neutral link.

My question is why would you opt to use a 3 pole and neutral link instead of a 4 pole switch? Surely a 4 pole switch is always safer as completely isolating equipment from all live conductors (I.e any feedback etc) to work on?

I am newly qualified, I can’t see anything specific about this in the 18th edition so am keen on the reasons why you would choose one over the other.

Cheers

 

[Pete999]

Most TP&N DBs come with interchangeable incomers, I know MG do at least

 

[Leesparkykent]

Some UPS setups use neutral as a reference so you could end up with an expensive headache if you disconnect the neutral.

 

[Sintra]

You can use a 3 pole switch on a TN system with a neutral link. If it is TT then you need to use a 4 pole switch. Don’t have a regs book to hand but it used to be in section 537.

 

[jay sean]

Back in the day when I used to be on the tools the sub boards were Merlin boards which were 3phase,
They all had 3pole switches with a neutral link, but Im sure in the main switch panel, the main switch would be a 4pole ACB,
This would have been a Tesco store done in the late 90s

 

[davesparks]

With a TN system there is no need to disconnect the neutral to achieve a safe isolation because the neutral is reliably connected to earth. By having the neutral switched at the main switch you introduce the possibility that the neutral contacts could fail and cause all sorts of problems so it is generally thought to be better to avoid adding an unnecessary potential point of failure.
Where there is a need for the neutral to be switched to avoid danger then it is of course necessary to provide this facility and it becomes a bit if a lesser of two evils situation.