TT Earth connection question

[Vessy]

Hi, need some advice on a TT earth path.

House has CU in hall and a smaller CU in garage which is supplied with 6mm T&E from a 32A MCB in the house, the earth rod is connected into the garage CU then the cpc from the 6mm routes this into the house CU, is this OK or should I get the rod connected direct to the house CU?

Everything protected by 30ma RCD's as required by regs for TT, the only other observation was garage CU earth connects to gas pipe (in garage) & house CU earth connects to water pipe.

Thanks.

 

[pushrod]

The submain is new and the house CU is older ? - so how was it earthed before the sub main was put in?

If i understand what you are saying then you effectively have the main protective bonding conductor from the water and the earth from the house CU, running into the 4mm(?) cpc in the 6mm T&E !!! This does not comply with BS7671. Min size for a main protective bonding conductor on a TT is 6mm and is governed by reg 544.1.1

Sounds like some changes are needed.

Where are the RCDs positioned?

Are you sure there is no earthing arrangement at the main cutout and the submain has not just been given a separate TT?

 

[Vessy]

House is only TT, right more info, CU originally was in garage, Tails extended into house and split load CU installed, existing garage CU reused to supply garage, feed for this is the 6mm T&E coming from the new CU.

Earth rod is original with 4mm conductor to the garage CU, basically the garage CU earth bar is being used as main earth terminal. This then feeds into the house CU using the 2.5mm cpc in the 6mm feed. BS7671 542.3.1 states that a TT size need not exceed 2.5mm when RCD's are used, all feeds are protected by RCD's in the house CU, nothing is unprotected.

Protective bonding is 6mm, gas pipe to main earth terminal in garage, water pipe to earth bar in house CU

Any thoughts?