UFER GROUND AND CANADIAN STANDARDS

[pristava]

UFER Ground is a conception of the Grounding where rebars -reinforcing bars from the concrete foundation have been used as a part of the grounding.
Is anybody knows anything about an application of UFER Grounds here in Canada. I didn't find any information in Canadian Electrical Code plus Ontario Electrical Code.
Is UFER Ground accepted by any Canadian Standard ?
I have a Design Package ( prepared by American Company)for the small Hydrogen Production, but I am really pessimist that UFER Ground can be accepted as Grounding System.
( hydrogen is very flammable gas)

 

[mc5w]

Talk to your local electrical inspector and bring some references with you such as the IEEE Green Book. There is a study that was done by Underwriters Laboratories and the Ufer ground was the 3rd best grounding electrode that can be used.

The Ufer ground was first used in Arizona and was found in their soil conditions ( dry and sandy ) to be an excellent ground.

 

[dpc]

I can't speak to Canadian codes, but there is little doubt regarding the effectiveness of Ufer grounds. These are actually **required** by the NEC whenever applicable. Reinforced concrete in most soil is a very good conductor. I would trust a well-installed Ufer ground over just about anything else.

 

[itsmoked]

They are required in CA.

 

[ruble3]

If you have a copy of the Ontario Electrical Safety Code look at section 10-702 -Artificial Grounding Electrodes-
does thsi cover it?

 

[EEJaime]

We use the UFER grounding system in conjunction with other grounding electrodes. What I do is bury a 40', (12 Meter) piece of bare copper cable, usually #4/0 AWG, cadweld it to the re-bar at each end and run your grounding electrode conductor cadwelded to this grounding electrode,(sized for your service), back to the main ground bus of your service panel. I also bond the building steel structure and the main water and gas mains in the building on the secondary side of the meter to the main bus. I have always gotten an excellent ground path with very good resistivity tests, regardless of soil conditions. The material is relatively inexpensive and easy to specify.

 

[RRaghunath]

IEEE 80 - Green book talks of drying effect in the concrete and loss of bond between steel and cement consequentially, due to the currents circulating if the earth mat conductor is bonded to the reinforcement steel in concrete.

My impression after reading IEEE was that the code doesn't recommend such bonding between earth conductor and the reinforcement steel in concrete.

Any thoughts / experiences??

Thanks in anticipation.

raghunath_n00@rediffmail.com

 

[mc5w]

Most basements here in the U.S. outside of the southwestern desert act a giant dug wells. This means that it is just about impossible for the concrete dry out.

Even in the southwestern desert you would need chronic current flow to dry out the concrete. This would only happen if you had an open neutral with consequent voltage fluctuations or a leaking underground electric line which would partially energize drain pipes and floor slabs leading to nasty tingle voltages. This is how you can get shocked by an applicance or water pipe that is properly grounded.

Even if the sanitary sewers are plastic there is a recorded instance of electricity crawling up the slime on the inside of a plastic drain pipe for a shower. Really got the howmeowner's attention. See Old Electrical Wiring by David Eli Shapiro.

I am also aware of a mobile home park that has tree and grass roots that are penetrating the joints of plastic sewer pipe that uses O-ring gaskets instead of solvent cement. The pipelines have to be bored out every year and then foaming herbicide injected into the pipelines. 2 of the advantage of gasketed joints are that they can be assembled with water running through them and each joint is an expansion joint. However, you do need to wrap the joints with copper foil to discourage the tree roots and grass roots.

 

[mc5w]

I also found out that the grounding electrode study is being done by the National Fire Protection Association research group, not by Underwriters Laboratories.

I can assure you that the Ufer ground is an excellent ground in part because the concrete increases the contact area with the soil. If you have a 30 foot by 30 foot house with typical 16 inch wide footers, then bonding to rebars or a copper wire that goes all the way around the footer give you about 120 square feet of soil contact. Compare that to how back in the days of telegraphs that used the earth as the return wire the preferred electrode was a 3 foot by 4 foot metal plate giving 24 square feet of contact with the soil. If you drive a rod underneath the footer where the grounding electrode conductor hooks up then you will have a low inductance ground for any lightning current that is coming in over the service drop.

A book on high performance grounding methods is Army Manual 5-690. I forget what the URL is but if you feed "army manual" and 5-690 into Google you should find it. This book cover things such as lightning rod systems, protection against heavy duty radio frequency interference, electromagnetic pulse protection, controlling signal leaks, and so forth. A rather heavy read but it has lots of drawings and diagrams to help you understand some concepts. It also has some tested methods of how to bond a waveguide or coaxial cable for which a listed grounding block is not available.

 

[jghrist]

The ufer ground depends on concrete being lower resistivity than the surrounding soil. This will be the case whether it is moist or dry unless the soil is of unusually low resistivity, in which case you probably wouldn't have much of a grounding problem anyway. If the concrete is dry, then the soil will be dry.

If the steel reinforcing bond with the concrete is lost, then grounding problems may be the least of your worries. The structural integrity of the foundation depends on this bond.

 

[pristava]

Can you repeat, please. What is better for UFER Ground ?
Concrete resistivity higher than surrounding soil or reverse ?

 

[jghrist]

Concrete resistivity lower than surrounding soil is better for ufer ground.

 

[mc5w]

Unless you build your building in a swamp the concrete will have lower resistivity than the soil. Please go over to

http://www.mikeholt.com

and subscribe to his grounding newsletters and also download the newsletters that have been published. Mike Holt recently published some excerpts from old telegraph manuals and scientific papers. One rule of thumb is that typical soil in the U.S. has about 1,000,000 times as much resistance as steel. Hence, a 3 foot by 4 foot grounding plate has a typical resistance about equivalent to 7 miles of #6 steel wire.

Early telegraph lines were made out of steel wire partly for mechanical strength and because long lengths of copper wire was just not manufactured. The mechanical strength issue was partly how copper clad steel wire was invented.

The 25 Ohm figure for an acceptable grounding electrode was originally that a 25 Ohm ground at each end would give very reasonable efficiency for a telegraph line say 50 to 100 miles long. In actuality, you need a 5 Ohm or better grounding electrode to stabilize an open neutral condition on a residential service enough to run a few light bulbs and alarm clocks overnight until an electrician shows up.