Garage SWA Earthing

[stuchunk]

Just a quick question,

Im in the process of taking 3 core 6mm SWA to the garage from the house CU, glanding into MK enclosure in the garage, using 3rd core as earth from house to garage enclosure, Im on TNCS supply do I connect the panhandle on the armour to the earth bar using a 6mm earth wire connection or is it optional/good practice as I am already using my third core as an earth back to the house CU???

 

[stuchunk]

Im on TNCS supply

Sorry should have read TNS supply, but anyhow just out of interest does it make any difference to my original question as to the connection of the armour to earth if I used my third core of the SWA as an earth??

 

[Adam_151]

You must earth the armour at the supply end to protect the cable (the idea s that if you cut into the cable with something, it'll be making contact with the armour before making contact with a conductor), If you are using a core as earth then you don't need to connect the armour at the load end, but doing so will lower EFLI a tad.

Only thing it being TNS or TNCS makes a difference for is whether or not you export an earth to an outbuilding, if its TNCS sometimes you might not and choose instead to use a rod and make it TT), or you might have a minimum size for a submain earth cable, TNS is largely free of these complications

 

[stuchunk]

or you might have a minimum size for a submain earth cable

Can you please expand on this for me please,I dont quite understand, is this something to do with a situation when the earth conductor in the SWA may not be of a sufficient size to be the submain earth?

 

[plugwash]

if the outbuilding is wooden and has no incoming metal services then there is no problem taking a PME earth to it.

the problem comes when there is something metal that needs main bonding (metal undeground pipes, structural metalwork in contact with earth etc)in the outbuilding. Then the earth to the outbuilding should meet the main bonding standards for the PME supply in question (e.g. be at least 10mm for domestic sized services)

 

[stuchunk]

the problem comes when there is something metal that needs main bonding (metal undeground pipes, structural metalwork in contact with earth etc)in the outbuilding. Then the earth to the outbuilding should meet the main bonding standards for the PME supply in question (e.g. be at least 10mm for domestic sized services)

Would I be right in saying then in this situation the easiest way to do this for a decent size shed or domestic garage would be to use a 3 core 10mm SWA or separate 10mm earth from the garage/shed to the house.
Obviously 10mm swa is not really required for a small metal garden shed so then you would just use a separate 10mm earth

 

[Adam_151]

Thats for a TNCS supply, you corrcted your post and told us you had a TNS supply?

I'll expand the point fully if you want to know, its if you take TNCS to the outbuiling and have services to bond in there then the earth in the submain cable becomes more than just a CPC and should be sized in accordance with 54H

Not entirely sure what would be most logical to do in a TNS outbuilding at has stuff to be bonded? I suppose you treat the end of the submain cable as if it was a supply from the REC and create a separate zone (although its likely to be very much the same potential), and then use the standard 0.5 rule for the bonding

[you have to be wary of earth cable sizes on TNCS dur to circulating network currents etc, which I beleieve is the point of 54H]

 

[Taylortwocities]

This article from IEE's Wiring Matters covers most of the issues. Hope it helps.

http://www.iee.org/Publish/WireRegs...matters_electrical_installations_outdoors.pdf

 

[plugwash]

Thats for a TNCS supply, you corrcted your post and told us you had a TNS supply?

but given some recs tendancies to convert TN-S to TN-C-S at the first sign of issues with the lead sheaths i'd be VERY tempted to follow TN-C-S standards even if the supply is currently TN-S.