Mains Isolator advice

[Jonny72]

Quick question. I want to put an isolating 2p switch on my incoming supply from the meter to the board. I want this to allow easier board changes in future. Tails are below the 3m. DNO have agreed to pull fuse to facilitate this work. Timing is perfect as they want to update meter and head. Such as switch will come in it's own enclosure. I assume under 18th Edition regs this needs to be non combustible material ie metal construction. I see alot of double pole switches even one by Wylex all of which are ABS plastic. If metal this will obviously also need to have an earth. Any recommendations of devices to use?

 

[timhoward]

Hi, 421.1.201 refers to 'consumer units and similar switchgear' in domestic premises.
The service isolator has generally not been considered to fall within this description., and the DNOs fit plenty that are not metal.

To my thinking it is preferable for it to be a non-conductive material, with a couple of earthing systems having their own 'good reason':
PME - you want to be able to turn it off without a metal enclosure being live if open PEN conditions exist
TT - a fault from Line to the container inside the service isolator wouldn't clear.

So I'd just use the products on the market, with the Wylex REC2 being quite popular.

 

[Jonny72]

Hi, 421.1.201 refers to 'consumer units and similar switchgear' in domestic premises.
The service isolator has generally not been considered to fall within this description., and the DNOs fit plenty that are not metal.

To my thinking it is preferable for it to be a non-conductive material, with a couple of earthing systems having their own 'good reason':
PME - you want to be able to turn it off without a metal enclosure being live if open PEN conditions exist
TT - a fault from Line to the container inside the service isolator wouldn't clear.

So I'd just use the products on the market, with the Wylex REC2 being quite popular.

Yes I was honestly thinking about going down that line. I have TNCS and aware having an earthed isolator could have issues if broken PEN was to occur. Thankyou.

 

[Vortigern]

The Wylex iso. has facility to insert seal at the end where the supply comes in which is why it is very often used by DNO.

 

[Mikegh]

Hi, 421.1.201 refers to 'consumer units and similar switchgear' in domestic premises.
The service isolator has generally not been considered to fall within this description., and the DNOs fit plenty that are not metal.

To my thinking it is preferable for it to be a non-conductive material, with a couple of earthing systems having their own 'good reason':
PME - you want to be able to turn it off without a metal enclosure being live if open PEN conditions exist
TT - a fault from Line to the container inside the service isolator wouldn't clear.

So I'd just use the products on the market, with the Wylex REC2 being quite popular.

If considering the open PEN wouldn't that therefore apply to all consumer units with a main isolator

 

[timhoward]

If considering the open PEN wouldn't that therefore apply to all consumer units with a main isolator

Yes. If you find a suspected open Pen you don’t want to touch a metal consumer unit.
Having a non-conductive upstream isolator is a good thing!

 

[pc1966]

The one I have kicking around still to be used in the Wylex RECSW2S which is slightly slimmer, and more importantly it has double clamp screws for each cable.

I think the main issue that prompted the regs to push for non-combustible enclosures was badly terminated connections overheating, so a combination of dual screws and the correct torque setting, plus a bit of settling/wiggling/re-checking torque should largely eliminate that risk.

 

[Jonny72]

The Wylex iso. has facility to insert seal at the end where the supply comes in which is why it is very often used by DNO.

 

[Jonny72]

Yes like that - fitted last week