Flat consumer unit change.

[Snapester]

Changing a consumer unit at a flat but have a few questions regarding earthing etc. supply is from 16mm T&E fed from the incoming supply cupboard in a separate building main supply is tn-c-s. Each flat is supplied from a 63amp switch fuse. So earthing to the flat is via the 6mm back to the switch then 16mm back to main supply ze measured at 0.16 at switch and 0.20 at CU.
Flats are bonded in 6mm.

What are regs in regards to bonding from switch tto board? Being a TNCS should it not be 16mm back to supply? Only trouble being its impossible to do this?

I haven't done many changes in flats and wondered what the ddeal with supplies as regs?

Thanks Ian

 

[Guitarist]

Changing a consumer unit at a flat but have a few questions regarding earthing etc. supply is from 16mm T&E fed from the incoming supply cupboard in a separate building main supply is tn-c-s. Each flat is supplied from a 63amp switch fuse. So earthing to the flat is via the 6mm back to the switch then 16mm back to main supply ze measured at 0.16 at switch and 0.20 at CU.
Flats are bonded in 6mm.

What are regs in regards to bonding from switch tto board? Being a TNCS should it not be 16mm back to supply? Only trouble being its impossible to do this?

I haven't done many changes in flats and wondered what the ddeal with supplies as regs?

Thanks Ian

Just out of interest, is the 16mm T&E from the main building protected in any way?

 

[Taylortwocities]

<HINT>
Your supply type might be tnc-s to the switch fuse, but what is the supply type from the switchfuse to the flat?

The Neutral and earth are no longer combined...................:wink5:

 

[Snapester]

Yes im hoping so I think it's ducted under the building it's about 30yrs
old.
I see what you are saying the supply is now essentially TNS?

 

[Snapester]

So bonding in the flat can be 6mm if the supply is classed as TNS?

 

[Amp David]

I'd check that the 4mm earth to each flat is ok too.

Surely the earthing is still TN-C-S though

Bonding is 10mm for your earthing system. Its only like putting a sub main into an outhouse or similar that has ECP in it.

One reason not to use TandE for submains, its nasty:furious3:

 

[Snapester]

Earthing is 6mm

 

[Amp David]

Earthing is 6mm

Quite right, thinking 16mm had 4mm CPC.

Sorry

Will still need to be confirmed though.

 

[Snapester]

Working with t as 0.1 on equation CSa of protective conductor works out at min of 4mm so 6mm will suffice for installation.
Can bonding stay as 6mm as its a nightmare to change in this flat? Noted as a departure?

 

[Guest123]

Quoted from ESC guidance......

Q12. When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?
Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded.

 

[Guitarist]

Quoted from ESC guidance......

Q12. When carrying out electrical work on an installation forming part of a TN-C-S system, is it necessary to upgrade existing 6 mm² protective equipotential bonding to 10 mm²?
Not necessarily. If the existing 6 mm² bonding connects all the extraneous-conductive-parts to the main earthing terminal, has been in place for a significant time and shows no signs of thermal damage, then it may not require to be upgraded.

This is always the excuse people give for not upgrading any installation tho..... "It's been working fine like that for years".