When do Neutrals need to be switched?

[MaintenanceSpark]

Sorry if this is a silly question but I can’t get an answer from colleagues as it’s a “I dunno”. So I thought I’d ask here!

Some of our TPN DB’s have a 3 pole main switch with a block for the neutral. Other TPN DB’s we have here have a 4 pole main switch which switches the neutral.

It’s the same for our machine isolators. Some have a 4 pole rotary switch and others have a 3 pole rotary switch with a connector block for the neutrals.

When do we need to switch neutrals & why?

Apologies again if it’s a silly question or something I should already know. I’d like to learn.

Thanks guys.

 

[mickegh]

Neutral is a "live" conductor so should generally be switched

Also even with TN where the neutral is reliably at earth potential it can be safer to switch

 

[MaintenanceSpark]

Neutral is a "live" conductor so should generally be switched

Also even with TN where the neutral is reliably at earth potential it can be safer to switch

Cheers mate. Whenever I change an isolator in the future I will always replace it with a 4 pole rotary switch isolator then.

 

[mainline]

Neutral is a "live" conductor so should generally be switched

Also even with TN where the neutral is reliably at earth potential it can be safer to switch

If the OP is talking about 3 phase, then the N is normally solid linked.
If the Neutral is switched, then the 4 pole switch should be late disconnect and early make.

 

[Risteard]

If the OP is talking about 3 phase, then the N is normally solid linked.
If the Neutral is switched, then the 4 pole switch should be late disconnect and early make.

Indeed. It can be more hazardous to break the neutral in this scenario.

 

[MaintenanceSpark]

Thanks guys. I’ll keep the neutral in a connector block link and keep it unswitched.

 

[MDJ]

Neutral is a "live" conductor so should generally be switched

Also even with TN where the neutral is reliably at earth potential it can be safer to switch

Id disagree, if a neutral hangs and single phase circuits connected in a TPN board then 400 volts can go across 230 volt connected equipment, seen it happen and generally as mentioned by Risteard can be hazardous

 

[mainline]

Id disagree, if a neutral hangs and single phase circuits connected in a TPN board then 400 volts can go across 230 volt connected equipment, seen it happen and generally as mentioned by Risteard can be hazardous

Hence, the need for late break early make isolator.

 

[mickegh]

Wasn't paying attention thought it was items of 3P machinery that was being isolated

 

[LeeH]

Bathroom fan?

 

[MDJ]

Bathroom fan?

Nothing wrong with having a 4 pole local isolator near the fan, but if single phase equipment is connected to a three phase board I would not switch the main neutral at the incoming DB switch, this is a discussion which could get quite intense if several sparks started debating it lol, however when you have seen a hung neutral like I have then you would not switch a neutral on single phase circuits if connected to 400 volt distribution.

 

[Marvo]

Our local regs (not UK) require both L+N to be switched if earthing arrangement is TT.

 

[MDJ]

Our local regs (not UK) require both L+N to be switched if earthing arrangement is TT.

Hi Mate, hows the old legs?

 

[Marvo]

Hi Mate, hows the old legs?

All good thanks, still trying to retire but still finding myself busy as ever. Hope you're well.