main earth query

[hughesy1982]

Hi guys! im wiring a barn conversion and am not sure what to do about the main earth to the building.

The barn that is being converted has no mains source to the building. The power source into the plot comes into another barn alongside which is having no renovation done at the moment. i have run a 25mm swa from a henly block to a 80a switch fuse from the incoming mains into the consumer unit into the barn conversion.

My query is can i use the spare core in the swa and connect to the main earth terminal at the mains end into the main earth terminal inside the consumer unit?

 

[telectrix]

how long is your SWA run? what is the existing earthing arrangement? there has recently been huge debate on this forum on whether to export the earth or TT the new installation. opinion is divided.

 

[malcolmsanford]

Is the barn conversion going to have it's own dedicated supply in the future?

Is the conversion going to be a dwelling?

Is there sufficient capacity for the extra load in that other barn?

What is the earthing system at the moment in the other barn?

Need some more infi really

 

[hughesy1982]

Thanks for the reply, Outside the barn with the power source is a metal clad box with the main incoming power it has an earth terminal in there which is what the barn that is not being converted is using as the main earth to the cu. the swa run is just under 40 meters.

Im personally thinking a rod by the new barn is needed but obviously if i can use the spare core in the swa for an earth ill use that as it the easier option.

 

[malcolmsanford]

IMO I will still like to know what the system is in that metal box, do a Ze and see what you get.

A 40 metre run is quite extensive I would be looking at TT the refurbished barn. If the 1st barn is say TNC-S you can Earth the SWA TNC-S and not connect at the refurbished barn CU to the SWA. You can in fact then run a 2 core SWA which over 40mts will be cost effective.

Then at the refurb barn sink a rod, so that any gas or water services can be locally bonded. This is just my opinon and how I would do it, I'm sure we will get many options, you'll just have to choose yours.

 

[Engineer54]

Where is the main earthing cable originating from, ...in the main supplies cut out box or from the incoming supply cable (ie cable armouring). If it's coming from the cutout box then you have a PME (TNC-S) derived system and a 40 mt run to the refurb barn is on the long side and maybe uneconomical, apart from anything else to retain the present earthing system. If it's coming from the incoming cable sheath then your in luck you have a TN-S system and can use the armouring and the separate core in your SWA to provide the refurb barn an earthing system.

Is the barn that has the supply, derelict?? I'm asking because if in the not too distant future it's decided to demolish the barn, what is going to happen to the supply for the newly refurbished barn??? In other words If the supply is not a secure supply then it's not a viable source of electrical supply...

 

[Deleted member 26818]

It's unlikely that any of the supply is going to be TN-C-S as it's agricultural.
Use either the spare core, or as is normally done in TN-S the cable sheath, or even both.

 

[Engineer54]

Spin,

Barns, normally mean an agricultural environment!!! If it is TN-S then he's in luck, and can take the earthing system with his cable. Over that distance, i'd be inclined to use both the armouring and the extra core... lol!!!