Old cu with 6mm earth - TNC-S

[timo]

Quoting for a job. Need to install a 1 way cu to feed shower as the exising is full and old none rcd unit etc.
noticed that the C.U is 16mm tails with only 6mm main earth. Do i need to alter this or just make sure my new 1 way is 16 with 25mm tails from splitter block.

 

[Deleted member 9648]

Size your own tails and earth according to the load on your 1 way CU,you will struggle to get 25/16 in a 1 way CU and are allowed to down rate in these circumstances...433.3.1.........434.3.
I would upgrade the existing main earth anyway,not exactly going to add much cost....and you will have to assess whether the existing 16mm supply tails to the henly will take the additional load of the shower....Dont forget the main bonding is unlikely to be adequate given the age of the install so you will need to allow for that as well.

 

[timo]

true, i could use 10/16 mm tails instead. The main earth to the exising CU is quite hard to replace as it ex council and they ran them in the cavity 2 foot then into the meter box. House just been all nicely decorated and new kitechen. water and gas in 6mm too. Customer not happy about taking brand new kitchen apart to run new 10mm earth to stop tap hmmmm

 

[Mr Mike]

I do simpathise with you and your client, but perhaps a bit of forthought may have been favourite.
Was the new kitchen decorated with additional sockets/lighting.
Hope it works out well for you and your client.

 

[timo]

New kitchen looks well yes but no new sockets or light points/fittings added. Wish they had been then somone might have sorted the earth and c.u lol

No other way of getting a 10mm in without going through the kitchen, plus all upstairs is new laminate flooring carpets

Starting to think about losing the quote in the mail. Dont wanna but.........grrrrr JOBS!

 

[PC Electrics]

The 6mm MPB is fine as long as it's in good condition.

see Q12 here:
Alterations and additions in domestic and similar premises : Electrical Safety Council

 

[telectrix]

also Q.5. the earthing for the alteration should be adequate for said alteration.

 

[geordie]

6mm earthing will be fine just check the continuity. Depending on the main fuse size the 16mm tails maybe ok

 

[Deleted member 9648]

6mm earthing will be fine just check the continuity. Depending on the main fuse size the 16mm tails maybe ok

A 6mm main earth on a TNCS is not fine.