Earthing Concrete?

[RogertheBodger]

Hi All.

Can I have some opinions please on the value of using Re-bar cages in a house foundation as Earth connections for a TT system, when encased in concrete do they make a good connection to earth, or not so good?

 

[mayfair]

Rodger dont even think about it m8, pm me if you want help with tt regs

 

[Lighthouse Phil]

Once the concrete is dry, there'll be no conductivity.....

 

[Engineer54]

In a nutshell, Yes they do make a pretty decent earth connection!!! My house in Cyprus, has it's re-bar cage forming part of my overall TT system, along with the swimming pool re-bar cage!!

If this is a new build, i would also take and earth rod or two and connect these to the re-bar cage. If you want to go a stage further, adding carbon dust or granules to the concrete mix, then you'll almost certainly be very close too, or better the magic 1ohm base line, ....depending on the ground soil type, the building slab is sitting on....

 

[Engineer54]

Once the concrete is dry, there'll be no conductivity.....

And where did you glean that information from then?? You couldn't be more wrong!!!

 

[mayfair]

Roger answered your PM if you need a boliten please dont let them in on the ring trick. some get the hump

 

[not clever]

100% agree with E54.
Infact I think you'll find the method is in GN8 lists of recognised earth electrodes.

 

[Engineer54]

Roger answered your PM if you need a boliten please dont let them in on the ring trick. some get the hump

Hahaha!! ....The ring trick works just Fine Mayfair, ...just that it can get a little costly to do it right!!

 

[mayfair]

Spot on m8 not forgeting a bit of underseal on the jubilee clips nod nod wink wink.

Hahaha!! ....The ring trick works just Fine Mayfair, ...just that it can get a little costly to do it right!!

 

[johnboy6083]

Hahaha!! ....The ring trick works just Fine Mayfair, ...just that it can get a little costly to do it right!!

Go on then, spill the beans on this ring thing? Is it multiple earthing points linked together?

 

[Engineer54]

If it is what i think Mayfair meant, ..... It's a bare copper ring around a given building, it could be connected to the slab re-bar cage (at various points), or 2 to 4 earth rods. ...2 earth rods if driven at diagonal corners, or 4 if roded at each corner. ....Or of course, connected to the slab re-bar and to the 2 or 4 rods!!...lol!!!

Where it starts getting expensive/costly is in the size of the building the bare copper ring needs circumvent, and the size of the bare copper conductor used. Also, because of the bare copper being directly buried, it really should be ''Hard Drawn'' copper conductor similar to that used on lightning protection installations. So as you see, a good overall system without a doubt, but can be a costly system to install too!!!

 

[Lighthouse Phil]

Well I stand corrected, its good to learn something new every day.
Was always my thinking that re-bar in dry concrete was useless, but after your comment I did a bit of googleing and so, as i said, I stand corrected.

 

[RogertheBodger]

Well I stand corrected, its good to learn something new every day.
Was always my thinking that re-bar in dry concrete was useless, but after your comment I did a bit of googleing and so, as i said, I stand corrected.

What did you find out?

 

[Lighthouse Phil]

Its one of the best methods there is. Some issues about exposed copper on the entry into the slab, but 5 or 6 inchs of sleeving will sort that.

 

[Lighthouse Phil]

Its one of the best methods there is. Some issues about exposed copper on the entry into the slab, but 5 or 6 inchs of sleeving will sort that.

Sorry, was to add this link for your info

Electric Power & Transmission & Distribution - Bare Copper Through Concrete

 

[johnboy6083]

How can the connection to the rebar be made without exothermic welding? Can jubilee clips be used, after all, the rebar is steel? What about the clamps for standard rods? I'm working on boreholes for a water board, and we are installing rods to reduce the potential to earth. This sounds like a much better idea.Another question, if the well pipe provides good contact to earth, as in this situation (upto 100m of pipe buried vertically), can this also be used in place of a rod, ie, put this to a BEMT, and bond everything to this, as well as the DB?

 

[mayfair]

Exactly what i was thinking about

If it is what i think Mayfair meant, ..... It's a bare copper ring around a given building, it could be connected to the slab re-bar cage (at various points), or 2 to 4 earth rods. ...2 earth rods if driven at diagonal corners, or 4 if roded at each corner. ....Or of course, connected to the slab re-bar and to the 2 or 4 rods!!...lol!!!

Where it starts getting expensive/costly is in the size of the building the bare copper ring needs circumvent, and the size of the bare copper conductor used. Also, because of the bare copper being directly buried, it really should be ''Hard Drawn'' copper conductor similar to that used on lightning protection installations. So as you see, a good overall system without a doubt, but can be a costly system to install too!!!

 

[mayfair]

How about this BTW i have not got a clue what its on about, so dont ask. It was a link in some Spanish regulations papers.
A proposed method for estimating the electrical conductivity of cement paste pore solution at 25 ºC is based on the concentrations of OH

, K

, and Na

. The approach uses an equation that is a function of the solution ionic strength, and requires a single coefficient for each ionic species. To test the method, the conductivity of solutions containing mixtures of potassium hydroxide and sodium hydroxide with molar ratios of 4:1, 2:1, and 1:1, and having ionic strengths varying from (0.15 to 2.00) mol/L, were measured in the laboratory and compared to predicted values. The proposed equation predicts the conductivity of the solutions to within 8 % over the concentration range investigated. By comparison, the dilute electrolyte assumption that conductivity is linearly proportional to concentration is in error by 36 % at 1 mol/L, and in error by 55 % at 2 mol/L. The significance and utility of the proposed equation is discussed in the context of predicting ionic transport in cement-based systems.

 

[malcolmsanford]

At this point should we mentioned that if the concrete is pre stressed then the ree-bar can not be used as an earth electrode

 

[Engineer54]

At this point should we mentioned that if the concrete is pre stressed then the ree-bar can not be used as an earth electrode

Extremely unlikely for prestressed concrete to be utilised as a foundation floor slab. Prestressed stuff normally comes as prefabricated sections...

 

[malcolmsanford]

Extremely unlikely for prestressed concrete to be utilised as a foundation floor slab. Prestressed stuff normally comes as prefabricated sections...

True mate but just thought I'd throw something else in to see if it sank lol

 

[Engineer54]

How can the connection to the rebar be made without exothermic welding? Can jubilee clips be used, after all, the rebar is steel? What about the clamps for standard rods? I'm working on boreholes for a water board, and we are installing rods to reduce the potential to earth. This sounds like a much better idea.Another question, if the well pipe provides good contact to earth, as in this situation (upto 100m of pipe buried vertically), can this also be used in place of a rod, ie, put this to a BEMT, and bond everything to this, as well as the DB?

The next best welded connection to exothermic welding, is ''braising''. Where exothermic or braise welding is not possible, then nothing wrong using clamps , either use Furse type, or U type clamps (say 2 or 3 to a connection). I would never use jubilee clips, far too thin and flimsy. I tend to wrap mechanical connections with amalgamating tape to protect the connection surfaces...


As for using those well pipes as your earth electrode, unfortunately not, you cannot use pipework from another utility or service as your means of primary earthing, ....those you ''Bond''!! It will however, give any electrical installation one hell of a good earth, once connected!! ...What!!!!....lol!!!

 

[malcolmsanford]

The next best welded connection to exothermic welding, is ''braising''. Where exothermic or braise welding is not possible, then nothing wrong using clamps , either use Furse type, or U type clamps (say 2 or 3 to a connection). I would never use jubilee clips, far too thin and flimsy. I tend to wrap mechanical connections with amalgamating tape to protect the connection surfaces...


As for using those well pipes as your earth electrode, unfortunately not, you cannot use pipework from another utility or service as your means of primary earthing, ....those you ''Bond''!! It will however, give any electrical installation one hell of a good earth, once connected!! ...What!!!!....lol!!!

I know your not a great lover of the old BS 7671-2008 mate, and don't use it over there, but you can use a water pipe as an earth electrode if it is a private pipe and not a utilities pipe, and precautions are taken against it's removal. ie you label it on a drawing or the pipe itself.

 

[Engineer54]

I know your not a great lover of the old BS 7671-2008 mate, and don't use it over there, but you can use a water pipe as an earth electrode if it is a private pipe and not a utilities pipe, and precautions are taken against it's removal. ie you label it on a drawing or the pipe itself.

On the contrary, i have the greatest respect for BS 7671, i may not agree with some aspects and areas, within it, especially regarding TT installations!! But still regard it as one of the better electrical regulatory publications around...

BS 7671 along with other BS's will actually be forming a good deal of my present project, ....But i do very much like the clause in the electrical specification appendix of the contract, that states, ''a higher international standard may be substituted at the direction of the the Engineer''....

Basically, if there is a higher spec available outside of the stated Appendix, say for in specific area's, i can call for that higher spec requirement to be followed....

Yes, I agree if it is a private pipe, and not a part of a utilities installation, it can be used as the primary means of earthing for an electrical installation. Not sure if i would contemplate doing so myself, it would depend very much on the circumstances, surrounding a given situation...

 

[RogertheBodger]

How about this BTW i have not got a clue what its on about, so dont ask. It was a link in some Spanish regulations papers.
A proposed method for estimating the electrical conductivity of cement paste pore solution at 25 ºC is based on the concentrations of OH

, K

, and Na

. The approach uses an equation that is a function of the solution ionic strength, and requires a single coefficient for each ionic species. To test the method, the conductivity of solutions containing mixtures of potassium hydroxide and sodium hydroxide with molar ratios of 4:1, 2:1, and 1:1, and having ionic strengths varying from (0.15 to 2.00) mol/L, were measured in the laboratory and compared to predicted values. The proposed equation predicts the conductivity of the solutions to within 8 % over the concentration range investigated. By comparison, the dilute electrolyte assumption that conductivity is linearly proportional to concentration is in error by 36 % at 1 mol/L, and in error by 55 % at 2 mol/L. The significance and utility of the proposed equation is discussed in the context of predicting ionic transport in cement-based systems.

It's amazing that you should bring this up Gary, it was to be my first job on Monday morning, just bought the bits today, what a coincidence!












(thought you were helping me?)

 

[RogertheBodger]

How can the connection to the rebar be made without exothermic welding? Can jubilee clips be used, after all, the rebar is steel? What about the clamps for standard rods? I'm working on boreholes for a water board, and we are installing rods to reduce the potential to earth. This sounds like a much better idea.Another question, if the well pipe provides good contact to earth, as in this situation (upto 100m of pipe buried vertically), can this also be used in place of a rod, ie, put this to a BEMT, and bond everything to this, as well as the DB?

Thanks for that Johnboy, you have reminded me that on site a number of micropiles have been sunk to support the new swimming pool, believe they have had to go down 20 - 30 Metres to bedrock, 100mm steel tube filled and lined with er what, some kind of slurry that was pumped in, might make a good connection?

 

[Engineer54]

Thanks for that Johnboy, you have reminded me that on site a number of micropiles have been sunk to support the new swimming pool, believe they have had to go down 20 - 30 Metres to bedrock, 100mm steel tube filled and lined with er what, some kind of slurry that was pumped in, might make a good connection?

If you can tap onto those steel micro piles that have been driven down 20 to 30 metres, then you stand a very good chance of gaining an excellent Ra level. Depending on the soil structure, you could very well achieve near or even better than TN levels!! ...And should remain good, for a good many years to come too!!!