Metal CU in garage T.T system

[rattlehead85]

Would like a bit of advice on how others have tackled this.
Got a situation where we have a TN-C-S supply to a house with a 6mm 2core swa feeding a detached garage using a T.T. Earthing arrangement with a service water pipe within the garage which has a 10mm bond to it. My question is the client has provided a new Metal clad Rcd 30mA front line board to install in the garage, what would be the best and most effective way of separating the earthed armour of the swa feeding the garage from the earthing system employed to the garage itself T.T. [emoji106]

 

[Leesparkykent]

Is the 10mm bond taken back to the house then? Why are you Making the garage a TT system?

 

[Silly Sausage]

Insulated gland

https://www.google.co.uk/url?sa=t&r...=ViAtnDwh-Gyx65z4VL9NVQ&bvm=bv.87269000,d.d2s

 

[rattlehead85]

Is the 10mm bond taken back to the house then? Why are you Making the garage a TT system?

No the T.T system and earthing to the garage was already in place as was the water pipe bond. The problem was the swa running into the garage was terminated into an old plastic smashed C.U with no gland used, the cable was just poked through a knock out. The client went and bought the metal board against my advice so now left with adequately terminating the supply cable whilst keeping the earthing separated and not exposed to simultaneous touch.

 

[spark 68]

Ideally the TT CU should be class 2, another way is to add an upfront 100mA RCD before the metal CU and obviously the armourings not connected at the TT side, alternatively a suitable insulated gland as Archy pointed out above ^^^ might be enough.

 

[Leesparkykent]

No the T.T system and earthing to the garage was already in place as was the water pipe bond. The problem was the swa running into the garage was terminated into an old plastic smashed C.U with no gland used, the cable was just poked through a knock out. The client went and bought the metal board against my advice so now left with adequately terminating the supply cable whilst keeping the earthing separated and not exposed to simultaneous touch.

why don't you drop the TT Earth and gland the SWA at both ends and use the SWA as the earth if the water bond in the garage is already connected back the MET in the house.

 

[spark 68]

why don't you drop the TT Earth and gland the SWA at both ends and use the SWA as the earth if the water bond in the garage is already connected back the MET in the house.

Because the sub-main is only 6mm, and inadequate for MPB purposes, 10mm minimum required for TNC-S

 

[Knobhead]

 

[rattlehead85]

why don't you drop the TT Earth and gland the SWA at both ends and use the SWA as the earth if the water bond in the garage is already connected back the MET in the house.

No the water is bonded back to the earthing within the garage. Cant see how you could drop the T.T. and connect the swa at both ends the water bond would then not comply size wise as the supply to the garage is only 2 core the armour on the 6mm aint big enough to carry the water bond back to source.

 

[Leesparkykent]

Because the sub-main is only 6mm, and inadequate for MPB purposes, 10mm minimum required for TNC-S

Yes I totally understand this especially after that other never ending thread lol.

Oops I took it as the water in the garage was bonded to the MET and the garage sub board had been made a TT system. Silly me lol

 

[uksparks]

But can you not just use the armouring as the earth as that will far exceed 10mm

 

[spark 68]

But can you not just use the armouring as the earth as that will far exceed 10mm

it doesn't lol

 

[rattlehead85]

But can you not just use the armouring as the earth as that will far exceed 10mm

Yes for earthing purposes not for Bonding.

 

[uksparks]

Why do you say it doesn't? It's 6mm 3core is it?

 

[Leesparkykent]

But can you not just use the armouring as the earth as that will far exceed 10mm

No as the resistivity of the SWA would not be adequate for the bonding.