earthing insulated raft foundations

[Highland build]

Hi,

 

Can anyone who has built an insulated raft foundation tell me what exactly they bought to attach to the reinforcement mesh to earth the slab?

 

Any links to products to buy or photos would be great as I'm going to need to have the right thing for next week. 

Thanks

[gravelrash]

new one..

Edited April 13, 2022 by gravelrash

[jack]

1 hour ago, Highland build said:

Can anyone who has built an insulated raft foundation tell me what exactly they bought to attach to the reinforcement mesh to earth the slab?

 

Any links to products to buy or photos would be great as I'm going to need to have the right thing for next week.

Who told you you need to do this? I've never heard of any such thing. It would take an awful lot of odd things to happen for a piece of rebar to become live inside cured concrete, and then for someone to come into contact with it.

 

In fact, our electrician used our house for his periodic inspection for ELECSA (or whoever he's with), and they told him he was overdoing it by earthing all the steels in the house.

[Happy Valley]

Put a copper roof on with an earth connection back down to the ground...

 

.... in all seriousness it should not be an issue. We have a two layers of steel mesh reinforcement in our 200mm concrete slab and rebar within our ICF but they are both completely encapsulated within the concrete.

Edited April 13, 2022 by Happy Valley

[TonyT]

The slab reinforcement makes a great earth conductor, you used to have to seek the structural engineers approval but think that’s dropped from the 18th.

 

The problem is the connection needs to be accessible for inspection, in the past, we used rebar shaped to go outwith the foundation and then bring the rebar into an earth connection chamber..

 

 

brazing used to be an option but again accessible is the requirement for future testing.

 

look at the furse website for more info

[PeterW]

4 minutes ago, TonyT said:

The slab reinforcement makes a great earth conductor,

Only if it is in contact with the ground and in this situation it is entirely encased with an insulator (the EPS). 

[Highland build]

@PeterW Yes its 250 EPS and then a 200mm structural slab with 2 layers of reinforcement, the manufacturer suggested an earth tale(not sure if that was typo and he means earth tape) and a spare duct next to it poppingup in the plant room but could someone whoes done an insulated raft explain how they did this and what they used exactly

 

[PeterW]

I’d be back to asking who needs this done ..?? It’s very rare to see earth bonding of rebar in a slab to anything as it is not exposed to anywhere outside the slab or have any connectivity to any other element unless there are J bolts or threaded bars attached to the reinforcing for any structural steelwork, but at that point you would earth the visible frame if required. 
 

 

[Temp]

I'd never heard of this but Google found..

https://www.cohesivehomes.com/rebar-grounded-or-grounding-rod#:~:text=Rebar on its own doesn,be a touch potential hazard.

Quote

 

Does Rebar Need To Be Grounded?

Rebar on its own doesn’t usually need to be grounded. If, however, the rebar is being used in a concrete slab you will need to ground the whole slab. This is because during a fault or lightning strike the ground and the concrete slab will be at a different potential and there may be a touch potential hazard. 

The steel reinforcement bars and meshes embedded in the concrete slabs are of high electrical conductivity because they are made up of a large metal cross-sectional area. The closeness of the two electrical conduits may cause arcing between them and damage the concrete or cause other damage. 

This grounding of rebar does have an advantage as it comes in useful as a grounding option. If rebar is already buried in concrete and a piece of it can be used as a grounding rod, this will be useful. 

 

 

[Russell griffiths]

I have seen this done in America. 

[gravelrash]

It would cause issues with earth bonding and difference in potentials. I could only think you would require it if the incoming power is live only and has no neutral/earth like taking a feed from an ancient supply line.

[TonyT]

So if it wasn’t insulated, let’s say a cow milking shed with animals that are large and wet.., you would need to ensure some of the rebar was welded together rather than tied, helps improve overall resistance .

 

not sure of the benefit in a standard house.

[SteamyTea]

Faraday Cage.

 

Just wanted to say it, I have nothing else to offer.

Edited April 13, 2022 by SteamyTea

[SuperJohnG]

I have an insulated foundation (Kore type) and don't have this...and never heard of it and I've read just about every thread on here about insulated foundations.  

[TonyT]

Possibly a cut copy paste specification….

[markc]

Assuming all reinforcing is clamped or welded then it can be used to enhance earthing and would simply need a cable and earth spike, but as you are unlikely to have a fully clamped or welded cage then it’s pretty pointless.

 

[willbish]

Isoquick mentions earthing the slab in their tech spec.

 

First electrician I engaged thought it was pointless but told me to fix an earth rod to the rebar coming up in the plant room. Second electrician saw the rod and cut it off

 

 

[Gone West]

As above we had an Isoquick insulated slab installed and they left an earthing tab which the electrician said wasn't needed so we cut it off.

[Radian]

11 hours ago, SteamyTea said:

Faraday Cage.

 

Interesting subject... large isolated conductive structure. Might be able to harvest a small amount of power from local radio transmitters. Or make it into a radio telescope if no transmitters nearby. If it were mine I'd definitely want to be able to make a connection to it.

[George]

I've only ever seen reinforcement earthed in electrical substations!

[JohnMo]

Bit lost with this.

 

Currently sat on a leather and wood chair, on a wooden covered floor, all of which are insulators, so even if my slab was or wasn't earthed, I am not.  The same would be true if stood bear footed upstairs in a timber kit house (wood floor support of wood structure).

 

So what's the difference if your slab is or isn't insulated from ground contact?  The UK has earth cables connected to every socket and switch in the house and these are run to earth.  All conductors (copper pipes etc) are run to earth.

 

Rebar should be covered by a min of 25mm of concrete in all directions, otherwise it suffers corrosion.  So is not accessible.

 

Might be needed in countries where an earth isn't routinely or mandatory to run - maybe USA? But seems a waste of time here.

[TonyT]

Rebar makes an excellent earth conductor so in a non insulated slab it can save time/effort later on…

particularly if you are trying to achieve 1 ohm for instance.

 

handy if you can’t export PME earth too

[Mr Punter]

I once had an issue on a house where the electrician would get a shock when he touched a wall light on the stairs.  It turned out that the wall light was fine but he had one foot on the stainless handrail to keep his balance.  The handrail installer had used a very long screw and this made the handrail live.  No issue until he provided a path to earth via the light fitting.

[Highland build]

On 13/04/2022 at 19:40, PeterW said:

I’d be back to asking who needs this done ..?? It’s very rare to see earth bonding of rebar in a slab to anything as it is not exposed to anywhere outside the slab or have any connectivity to any other element unless there are J bolts or threaded bars attached to the reinforcing for any structural steelwork, but at that point you would earth the visible frame if required. 
 

 

It just advices this earthing the reinforecement mesh

in the isoquick guidance, i spoke to my electrician in a brief call as he was on holiday in Lanzerote and he said this is total overkill

Did anybody with a raft foundation do this?? please send advice and insulated raft people

[Highland build]

On 14/04/2022 at 15:46, JohnMo said:

Bit lost with this.

 

Currently sat on a leather and wood chair, on a wooden covered floor, all of which are insulators, so even if my slab was or wasn't earthed, I am not.  The same would be true if stood bear footed upstairs in a timber kit house (wood floor support of wood structure).

 

So what's the difference if your slab is or isn't insulated from ground contact?  The UK has earth cables connected to every socket and switch in the house and these are run to earth.  All conductors (copper pipes etc) are run to earth.

 

Rebar should be covered by a min of 25mm of concrete in all directions, otherwise it suffers corrosion.  So is not accessible.

 

Might be needed in countries where an earth isn't routinely or mandatory to run - maybe USA? But seems a waste of time here.

Everyone i have discussed this will is giving a similar sort of reponse