TT system

[dal_87]

Hi doing a cu change at weekend 8 way dual rcd on a 100amp fuse and first time doing one on a tt system noticed that main bonding looks to be a 6mm and so is bonding to gas and water looked at some posts and people say is ok but regs state 16mm main earth and 10mm bonding do I change it all and follow regs book as I should do or is earthing ok as it and will I affect it if I upgrade earthing size. Also are the 16 mm tails fine ? Thanks

 

[Badged01]

Always interesting debates on dual RCD’s for TT systems.

Taking that the 30mA RCD is almost always required for additional protection on domestic circuits, can this 30mA RCD also be used to provide fault protection? (Assuming the TT system circuits can’t meet disconnection times.)

Or do we need two RCD’s? The main switch RCD at 300mA covering all circuits for disconnection times (or whatever RCD value is appropriate to the Zs value) and the 30mA additional protection RCD covering those circuits needing additional protection?

I guess it depends on how you interpret the likes of 415.1.2 in relation to the use of RCD’s for protection??

 

[D Skelton]

A dual 30mA RCD board will provide fault protection for any circuits that cannot meet disconnection times and also additional protection for any circuits that need it. Installing a dual RCD board, so long as it's class 2, is all that the regulations require if you haven't got a TN Ze value. That said, it would be prudent to install a 100mA s-type up front (either as the main switch or in a seperate enclosure) as a back up should one of the two 30mA RCDs fail. In fact, I'd go one step further and say that you'd be mad not to!

 

[Knobhead]

You’ve hit the nail on the head with the use of a time delayed S type. The 100mA mentioned by the OP is liable to be a bog standard unit so discrimination under fault becomes a bit of a lottery.

 

[telectrix]

if i remember, i advocated the use of a time delay 100mA in post #2.

 

[brucelee]

If your installing SWA to supply a garage Then buy a High Integrity CCU that has a number of ways unprotected so you can just install a CB and it separate from the 30mA RCD' s and then install the 100mA S-type RCD upfront or as the main switch to meet disconnection times and the small garage CCU will probably come with a 30mA RCD as the main switch

Your Swa would be protected and so would your final circuits

 

[dingledong]

Ask the supplier to change to pme , I have twice and both times they have done it for free I am in essex also !

 

[tony mc]

Ok I leave it in and still have dual cu it just looks rather dated but it can't be seen

Be careful read the other posts re type S RCD do not just leave it in check that it is a time delayed type which I doubt!

 

[Knobhead]

You may as well talk to yourself around here.

 

[dingledong]

Tony it's the only time I have a good conversation when I talk to myself

 

[Geordie Spark]

Ask the supplier to change to pme , I have twice and both times they have done it for free I am in essex also !

Ah yes ...... Essex - Twinned with Sunderand; "Bend over that bin pet, drop yer keks and keep tight a hold of your kebab and I promise I'll phone you in the morning".

 

[tidyboiler]

Ah yes ...... Essex - Twinned with Sunderand; "Bend over that bin pet, drop yer keks and keep tight a hold of your kebab and I promise I'll phone you in the morning".

Is that the Christmas one? "No "L" ........ "No L"............. the angels did say............... :carolers::christmastree1:

 

[dingledong]

Ah yes ...... Essex - Twinned with Sunderand; "Bend over that bin pet, drop yer keks and keep tight a hold of your kebab and I promise I'll phone you in the morning".

You old romantic

 

[Geordie Spark]

Is that the Christmas one? "No "L" ........ "No L"............. the angels did say............... :carolers::christmastree1:

Aye ... as in sammon

 

[tidyboiler]

Aye ... as in sammon

:19: cheeky boy!!!