4 pole rotary isolator... Switch the neutral or not?

[BodgeJob]

Hi there,

Just a quick question. I am rectifying many problems on some 3 phase immersion heater circuits in a plant room. There are 4 pole rotary isolators just before the immersion elements and the earthing arrangement is TN-S.

I noticed that the neutrals are connected into a dedicated linking terminal to the side, as opposed to the 4th pole on the isolator. Is this acceptable? Also, is it UNacceptable to wire the neutrals into the 4th pole of the isolator as a means of isolating the neutral? Would this cause damage to equipment?

I understand that the neutral is deemed to be reliably connected to earth (TN systems), so the neutral doesn't necessarily present a shock risk etc.

I also understand that isolating the neutral before the line conductors can result in overvoltages and appliance/equipment damage etc. The use of late break, early make switches for the neutral can help to overcome this etc.

And of course, if it was a TT earthing arrangement, the neutral should be switched anyway (neutral not reliably connected to earth).

At the moment, I am very much on the side of not isolating the neutral, as it is a TN earthing arrangement and this would prevent equipment from potentially being damaged. Basically, what I am asking is, is this correct?

Kind regards.
BodgeJob

 

[westward10]

If the elements are connected in star the neutral probably isn't doing a great deal.

 

[James]

If the elements are connected in star the neutral probably isn't doing a great deal.

If they are delta connected, it is probably doing even less!

 

[MDJ]

Hi there,



I noticed that the neutrals are connected into a dedicated linking terminal to the side, as opposed to the 4th pole on the isolator. Is this acceptable?

Kind regards.
BodgeJob

Absolutely, sounds perfectly normal to me

 

[Ala100]

In TN-S systems, you shouldn't isolate the neutral in a 4-pole isolator. Connecting neutrals to a dedicated terminal is acceptable and safe. Isolating the neutral can lead to dangerous overvoltages and equipment damage. So yes, you're right not to isolate the neutral.Additionally, remember that in TN systems, the neutral is grounded, reducing shock risk. In TT systems, the neutral should always be switched. Your approach is absolutely correct; stick with it!