10mm T&E CU change.

[Bobble23]

Hi,

I've been asked to change a CU in a converted one-bed flat immediately above the cellar which contains the TNS supply. The existing CU is currently supplied by a 6m run of clipped direct 10mm T&E protected by a 63A switch-fuse in the cellar. It's a small flat, haven't worked out maximum demand yet but am guessing about 45A. Main bonding goes direct to a MET in the cellar so I don't think that's an issue.

Just want to check a couple of things:

i) Is there any need for me to upgrade the supply to the CU? Also, do I need to add RCD protection before the new CU even though it's clipped direct?
ii) Is the 4mm cpc in the T&E good enough as the earthing for the new CU?

Thanks.

 

[Sintra]

1. No need for RCD if clipped direct
2. Work out using the adiabatic equation.

 

[GLENNSPARK]

Hi,

I've been asked to change a CU in a converted one-bed flat immediately above the cellar which contains the TNS supply. The existing CU is currently supplied by a 6m run of clipped direct 10mm T&E protected by a 63A switch-fuse in the cellar. It's a small flat, haven't worked out maximum demand yet but am guessing about 45A. Main bonding goes direct to a MET in the cellar so I don't think that's an issue.

Just want to check a couple of things:

i) Is there any need for me to upgrade the supply to the CU? Also, do I need to add RCD protection before the new CU even though it's clipped direct?
ii) Is the 4mm cpc in the T&E good enough as the earthing for the new CU?

Thanks.

if the twin bothers you then you could fix a bit of metal trunking in the cellar where it runs....a bit of mechanical protection...but like sintra says...

 

[Welchyboy1]

Hi,

I've been asked to change a CU in a converted one-bed flat immediately above the cellar which contains the TNS supply. The existing CU is currently supplied by a 6m run of clipped direct 10mm T&E protected by a 63A switch-fuse in the cellar. It's a small flat, haven't worked out maximum demand yet but am guessing about 45A. Main bonding goes direct to a MET in the cellar so I don't think that's an issue.

Just want to check a couple of things:

i) Is there any need for me to upgrade the supply to the CU? Also, do I need to add RCD protection before the new CU even though it's clipped direct?
ii) Is the 4mm cpc in the T&E good enough as the earthing for the new CU?

Thanks.[/]

63a is just inside the capabilities for a clipped 10mm

no rcd required for the submain

 

[BES]

Thought you couldn't use adabatic for main earth ?

 

[Plonker 3]

Its not a main earth though is it, its a sub main.

 

[BES]

Its not a main earth though is it, its a sub main.

Sorry carry on

 

[Geoffsd]

Thought you couldn't use adabatic for main earth ?

Why not?

 

[BES]

Thought you couldn't use adabatic for main earth ?

Why not?

Have a look in osg pg 40-41 table 4.4(I) and note 2 of table

 

[Jay Sparks]

The adiabatic is used for the main earth and the bonding conductors have to be no less than 50% size of the main earth result. A lot of people think that if the main earth is 16mm then the bonding to gas and water etc has to be 10mm. But if the equation shows that the main earth size can be, say 10 mm, then the bonding can be 5mm or above, so 6mm. It doesnt matter if there is a 16mm main earth installed.
The OP needs to do the adiabatic equation to see if the 4mm is acceptable.

Jay

 

[MDJ]

Have a look in osg pg 40-41 table 4.4(I) and note 2 of table

you could give some info on where it is in the BGB, most guys here have used the OSG for wiping their arses when they have run out of loo roll.

 

[Jay Sparks]

you could give some info on where it is in the BGB, most guys here have used the OSG for wiping their arses when they have run out of loo roll.

I don't/wont go for a number 2 on site unless I am wetting myself through my ---...lol So my OSG is in tact. But I have used it to hit trainees a few times..lol

 

[Geoffsd]

Have a look in osg pg 40-41 table 4.4(I) and note 2 of table

That's not right.

Have a look at the actual regulation 543.1.4
This thread is about TN-S.

Don't rely on the OSG.

 

[Engineer54]

The adiabatic is used for the main earth and the bonding conductors have to be no less than 50% size of the main earth result. A lot of people think that if the main earth is 16mm then the bonding to gas and water etc has to be 10mm. But if the equation shows that the main earth size can be, say 10 mm, then the bonding can be 5mm or above, so 6mm. It doesnt matter if there is a 16mm main earth installed.
The OP needs to do the adiabatic equation to see if the 4mm is acceptable.

Jay

Think you'll also find, it states 6mm as a minimum for a bonding conductor. You wouldn't i hope, use the adiabatic equation minimum size conductor on a new installation for either main earthing conductor or main bonding conductors....

 

[Jay Sparks]

Think you'll also find, it states 6mm as a minimum for a bonding conductor. You wouldn't i hope, use the adiabatic equation minimum size conductor on a new installation for either main earthing conductor or main bonding conductors....

Well seen as I've not actually come across any 5mm earth cable before, then of course it would be 6mm. I was only using it as an example. And I only use this equation when doing EICR's and on existing installations. On any new install, I will fit the required size main earth and bonding.

Jay