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.

 

[Engineer54]

As this is a separated self contained flat, any main bonding to extraneous pipework within the flat, should be going to that flats EMT, not to the MET of the building. The 10mm T&E's 4mm CPC is therefore in my opinion not suitable. A separate 10mm earth conductor should be provided from the flats CU or EMT to the installations MET... Personally i would never use T&E for supplying self contained CU's in a multi dwelling building...

 

[MDJ]

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.

I cannot see that reg in my book Geoff lol, it jumps from 543,1.3 to 543.2 haha, plenty of tables in between, I do however see what your refering to.

 

[Geoffsd]

It is on page 162 under Table 54.6