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Bonding of Earthing Conductor to Rebar

05/26/2014 11:37 PM

Hi allI am working in Saudi Arabia.I so in FURSE catalogue accessories for bonding the earthing conductor to the Re.Barof the building foundation / columns ....etc.Some people advised that it is not preferred to apply the same as the Re.Bars are not in direct contact with the soil.They added that the Earthing and Lightning Protection Systems are to be completely independent and not connected to the reinforcement.Please direct me on the following:
I) Correctness of above.
II)What is the harm on the building if the earthing network is bonded with the Re.Bars?
III) In case of using Piling system for foundation , is there any harm to bond the earthing network with the steel of said piling ??
Many thanks in advance for your kind anticipated feedback

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#1

Re: Bonding of Earthing conductor to Rebar

05/27/2014 12:01 AM

There are many reasons some people advise against these practices.

If you don't know the reasons yourself, you can kill people.

Look at the regulations and codes for your area.

Otherwise, don't do anything.

The Saudi Arabian Grid Code Issue: 01 Revision: 00 May .. may help.
Don't ask strangers for advice.

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#2

Re: Bonding of Earthing conductor to Rebar

05/27/2014 12:43 AM

I ran across this, it's call a Ufer ground. But as Lyn stated, follow your local electrical code. I myself, prefer a separate solid copper electrode for earth ground, but there again, the soil is going to dictate what and how you place your earth ground. Follow you local building code.

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#3
In reply to #2

Re: Bonding of Earthing conductor to Rebar

05/27/2014 1:28 AM

Thanks for the prompt responses from you and Lyn.

I have checked the documents that is advised by Lyn but there is no article stated on subject of my request.

Best Regards,,,

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#4
In reply to #3

Re: Bonding of Earthing conductor to Rebar

05/27/2014 1:34 AM

It is your responsibility to find the documents that control earthing of electrical systems in your area.

Do a search. That's probably how you found this site.

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#16
In reply to #2

Re: Bonding of Earthing conductor to Rebar

05/28/2014 9:19 AM

NEC 250.50 and 250.52. -- JHF

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#5

Re: Bonding of Earthing conductor to Rebar

05/27/2014 3:34 AM

Just thinking out loud here:

  1. rebars are rebars, electrical system is an electrical system both have an entire different functionality.
  2. you are not asking us why you can not use the rebar as return path for your electric so why use it as earthing system?
  3. can rebar be exposed in the structure? Yes no?
  4. are your piles maybe visible in the basement
  5. I) Common sense says it would be that way
  6. II) you could kill people
  7. III) induced electricity might damage your rebar.
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#6
In reply to #5

Re: Bonding of Earthing conductor to Rebar

05/27/2014 7:48 AM

Thanks for the reply.I concur with your opinion ( just on logic basis ) but the question is if the principle is as you have kindly explained Why the manufacturer " FURSE " produces accessories for bonding of the Earthing conductors with the Re.Bars ??Also please note that some installers do use the same which is known as "Ufer Ground"?
Best Regards,,,

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#7
In reply to #6

Re: Bonding of Earthing conductor to Rebar

05/27/2014 8:38 AM

No joy over the phone with Furse, then?

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#8
In reply to #6

Re: Bonding of Earthing conductor to Rebar

05/27/2014 8:49 AM

Maybe the answer is in between. Since the "Ufer Ground" is concreted in it will be similar in design to rebar or rebar is even used for this ground. That being said I would still separate it from the rebar rebar and not use the "ufer ground" as structural part of the building. It would not make sense since you want to have it separated from the real rebar anyway. By furhter thinking I would say that the connection of the "ufer ground" would be looking like it connects to rebar because it is connecting to a sort of rebar material.

Would that make sense?

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#9
In reply to #6

Re: Bonding of Earthing conductor to Rebar

05/27/2014 10:07 AM

Not sure about the methodology where you are at however a point to consider:

If the building is of steel frame construction, the column base plate bolts are usually installed wherein they are physically attached to the foundation rebar cage.

The NEC requires that all exposed metal surfaces in a building are earthed/grounded and usually the columns are bonded to the equipment electrical ground using exothermic welding.

In many cases the rebar is required to be welded to the base plate bolts or bonding jumpers are installed between the rebar and the base plates and/or base plate bolts.

My understanding is that this is done to prevent galvanic corrosion damage to the rebar, base plate bolts, and the base plate caused by a difference of potential.

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#10
In reply to #9

Re: Bonding of Earthing conductor to Rebar

05/27/2014 11:30 AM

<...this is done to prevent galvanic corrosion damage to the rebar, base plate bolts, and the base plate caused by a difference of potential....>

  • The Hong Kong Mass Transit Railway substructure suffered as a result of leakage traction currents from the DC return rail into the concrete and the rebar, reportedly. The solution was to reverse the potential of the conductor rail and the return rail so that the rebar did not corrode.

However, what the original poster is talking about is the earth path that only carries current briefly during a fault event, which is completely different. It is an answer, though not yet as convincing as it might be.

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#11
In reply to #10

Re: Bonding of Earthing conductor to Rebar

05/27/2014 11:58 AM

Agreed. Good point.

A good example of "after the fact" damage occurring to a structure despite accepted methods being followed.

I have witnessed some very strange, bizzare corrosion conditions when working on equipment and underground structures at different sites that were/are protected by cathodic protection systems.

The reaction varies significantly when going from one site to the other wherein the soil and ambient conditions change dramatically.

I have witnessed conditions at electrical generating stations and petroleum processing plants wherein the polarity of the cathodic protection had to be reversed to offset the induced conditions presented by the site equipment.

As always everyone has a theory but at the end of the day the only way to eliminate the guesswork was/is to perform "trial & error" actual in-field experiments and record the results over a period of time.

In some cases the results at one site were manifested as evident and significant in nature much faster than at others. (Days vs weeks or months)

Provoking arguments ensue as to which theory is correct and/or applicable but I tend to take the "lazy way out" and once the "fix" is physically proven, I lose interest quickly in arguing which theory prevails.

In this case the connections being under and within the foundation of a building, the field study is pretty much impossible which puts the structure and personnel in the vicinity "at-risk" without their being aware.

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#17
In reply to #6

Re: Bonding of Earthing conductor to Rebar

05/28/2014 9:37 AM

Using the rebar as the source for a ground is not a good idea, a proper connection to earth should be used, however, there are some reasons to bond the rebar together and tie it to a good established ground. This is probably the reason for the connection equipment being available. Back in the 1930's my dad had a real challange when he tried to install a radio tower on top of the Goldwater building in Phoenix. The building metal supports were not bonded together and the transmission frequency was not stable. Several month's were required to sort out the problem. I have since found many cases of wireless communications for processes in factories that had problems due to isoated metal structures (and rebar) that was not tied together. It makes sense to bond them together and tie them to ground, but that should not the source of the earthing connection.

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#12

Re: Bonding of Earthing Conductor to Rebar

05/27/2014 8:36 PM

We used Ufer earthing in most of our substations.
The wall footings and the slab rebar had copper tapes thermic welded to them at intervals around the switch room before pouring the concrete. There are carbon additives that can be included in the mix in place of aggregate. We didn't use them, but we were cement manufacturers so we should get it right.
The rebar itself doesn't need any special inter connections between the various mats as the concrete acts as the conductor.

To be honest the foundations weren't my problem so I didn't really get involved until running the tape from the MET around the walls and picking up the various tapes from the rebar.

The Ufer earth was an addition to the earth nest and bonds to the plant structural steelwork. The later substations didn't even have an earth nest as the ground area of the plant steelwork was deemed sufficient.

Furse market a high conductivity concrete, this is primarily for bedding the earth rod where the bed rock has been deep drilled. It increases the conductive area of the earth rod. It's lighter and not as strong under compression that a normal mix.

In the UK the electrical functional earth and the lightning ground rods should be connected.
From memory there should be only one connection between the lightning system and the MET to facilitate testing. There is also a requirement that the connection to the lightning system must be below ground level and not utilising the down leads.

You really should be talking to Furse.

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#22
In reply to #12

Re: Bonding of Earthing Conductor to Rebar

07/15/2014 9:51 AM

Quite. See #7 above.

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#13

Re: Bonding of Earthing Conductor to Rebar

05/27/2014 11:59 PM

Read so many comments claiming that earthing of reinforcement will kill people. Can not understand how?

In fact if the complete building is at earth potential, it is safer than otherwise.

And if rebars of piles are at earth potenial and so are any Cu pipes buried in the vicinity we protect rebars from Galvanic Corrosion.

Not only rebars but the Cu plumbing pipes buried or exposed in the building services (it is common to use Cu plumbing in Middle East, at least till 1997, when I left Dubai) for the same reason explained above.

But a point of Caution that we shall not depend only on Re Bars as Primary Earth for the building. For safety of personnel and proper operation of all electrical protection primary earth shall be provided as per local codes.

The disadvantage of earthed re bars can be that it may filter UHF signals of mobiles - but for this other gadgets are available. Contrary to this earthing of re bars is helpful in Radar and Radio stations etc as this will add to earth screening/ shielding provided. Similarly in HV test labs as this will add to arresting escape of electromagnetic emission on flash over.

So one has to weigh the situation and decide.

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#14

Re: Bonding of Earthing Conductor to Rebar

05/28/2014 4:00 AM

this is not a place where you can get ideas for serious projects. too many junkies here.

http://www.earthing.com/SearchResults.asp?Cat=1832

http://admin.copperalliance.eu/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/FinalDownload/DownloadId-03FAF5CD075A6EECD753A00B002FDB8E/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/docs/librariesprovider5/power-quality-and-utilisation-guide/651-earthing-systems-basic-constructional-aspects.pdf?sfvrsn=6&sfvrsn=6

http://www.pfeiffereng.com/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/FinalDownload/DownloadId-0E616CBBDFFA95345F1368843BCB5D95/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/Principals%20of%20Electrical%20Grounding.pdf

http://www.solacity.com/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/FinalDownload/DownloadId-2754620FFF49211A2D419BCD654CD921/7A8EEDF1-F0F3-4A55-9328-93665C59BA18/docs/erico%20-%20practical%20guide%20to%20electrical%20grounding.pdf

don't be too lazy to research, read own your own.

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#21
In reply to #14

Re: Bonding of Earthing Conductor to Rebar

06/13/2014 4:20 PM

I totally agree with you about junkies.

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#23
In reply to #21

Re: Bonding of Earthing Conductor to Rebar

07/16/2014 4:05 PM

In reply to both you and DmanEng (14), if this site has so many "Junkies", why the hell do you guy's keep coming back??

The only junk answer you will receive is from either, a junk question, (like home work or your claiming to be an Engineer but yet ask remedial questions), or your reply answer is so far out in left field,(US baseball) that your answer is ..... junk

That's the only junk replies I've seen here on CR4.

You will receive what you asked for, most of the time.

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#15

Re: Bonding of Earthing Conductor to Rebar

05/28/2014 7:19 AM

Furse makes the product so the entire building can be bonded as such. You do not want pilings (Structure) supporting a building not bonded together.

As for bonding the building itself to the Earthing and Lightning protection systems, that is another matter for the local code itself. Please check with your local inspector.

Best Luck!

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#18

Re: Bonding of Earthing Conductor to Rebar

05/28/2014 9:52 AM

I always used Erico CADWELD connection. If it was well executed no corrosion problem was remarked.

http://www.erico.com/public/library/fep/LT0355_08.pdf

However, there is another problem:

The short-circuit current flowing through rebar could heat the rebar at a high temperature-above the temperature of the water accumulated in concrete which could boil and the steam produced exploded the concrete. Then one has to check the maximum reached temperature is limited to 80-90 degrees C. See: IEEE-80/2000 CH.14.6 Concrete-encased electrode.

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#20
In reply to #18

Re: Bonding of Earthing Conductor to Rebar

05/29/2014 12:08 PM

"The short-circuit current flowing through rebar could heat the rebar at a high temperature-above the temperature of the water accumulated in concrete which could boil and the steam produced exploded the concrete."

If you have that much current going to ground for that much time to vaporize water in the surrounding concrete encasement, you will have bigger problems to deal with, like putting out the fires caused by faulty circuit protection.

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#19

Re: Bonding of Earthing Conductor to Rebar

05/28/2014 12:41 PM

Are you able to drive a copper rod to a damp layer of soil? The armoured sheath of the incoming power cable is connected to the transformer earth - or should be. It would be wise to include it in your protective connections.

Piling sounds good.

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