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#85485 - 07/08/03 03:26 PM ground rings
Cindy Offline
Member

Registered: 06/23/01
Posts: 196
Loc: PDX, OR, US
250.52A4 says "A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG."

Circle: Ellipse in which the two axes are of equal length; a plane curve generated by one point moving at a constant distance from a fixed point.

Encircle: Form a circle around.

so... not many circular buildings... we can assume that we probably don't need to form a perfect circle around the building, but do you assume that going completely around the builidng is required? some guys tell me that it doesn't really mean what it says about encirlcing the building, just use at least 20 feet of 2awg Cu... but how is that as good as a ufer since that is ok as an alternative? so i don't buy that... but then again, if you calculate a 20 foot circumference around a building, then it would probably be a dog house.

so my question is.... what does the NEC intend for us to do if we decide to use a ground ring? entirely encircle the building? go 20 feet along one side of the building?

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2014 / 2011 NEC & Related Books and Study Guides
#85486 - 07/08/03 03:33 PM Re: ground rings
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
The only ground rings I have done do encircle the building with a numerous taps to rebars and building steel.

One I am working on lately will be well over 3500' of 4/0 bare.

But perhaps these have been more than a NEC ground ring.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#85487 - 07/08/03 07:49 PM Re: ground rings
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
In my opinion a ground ring must ring the building or structure and have a minimum length of 20'
Don
_________________________
Don(resqcapt19)

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#85488 - 07/09/03 06:33 AM Re: ground rings
ThinkGood Offline
Member

Registered: 08/07/02
Posts: 1084
Loc: Milwaukee, WI
Cindy:

I can't answer the specific question as to the NEC's intentions relative to ground rings.

Is there a distinction made between a ground ring used for the grounding electrode and a ground ring used for situations where lightning-protection is required (towers...)?

If I understand correctly, any "extra" grounding systems (lightning, radio transmission, etc.) need to be tied in with the electric system anyhow.

P. S. Here are some links I found:
http://www.psihq.com/iread/ufergrnd.htm http://www.cpccorp.com/deep.htm

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#85489 - 07/09/03 10:50 AM Re: ground rings
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
iwire — Is your nice "3500' of 4/0 bare" 19 strand, or 7 strand, or something else?

[with respect to corrosive soil]

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#85490 - 07/09/03 01:01 PM Re: ground rings
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Bjarney That is a great question the stuff the office ordered was 19 strand and when I checked the job specs there was no requirement for the number of strands.

I just ordered some more and got 7 strand.

This is an addition to a building and the 3500' includes the original portion that I am adding to, the original is 19 strand 4/0 bare 10 years old, looks real bad.

It took a lot of wire brushing to get good material for cad welding.

Bob
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#85491 - 07/09/03 02:11 PM Re: ground rings
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Bob, I asked because 7-strand has ~61% of the surface area of 19-strand for the same cross-sectional area. Soil corrosion seems to vary quite a bit across the country. The “double-edged sword” of sorts is that more corrosive soil usually makes for lower ground-electrode resistance, which is usually desirable, but then, corrosion affects the working life of buried conductors.

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#85492 - 07/17/03 03:55 PM Re: ground rings
tdhorne Offline
Member

Registered: 03/22/01
Posts: 344
Loc: Maryland, USA
I had always believed that the twenty foot minimum was to cope with well houses, gaurd shacks, and similar small structures in order to insure that there would be not less then twenty feet of wire in contact with the soil.
--
Tom
_________________________
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison

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#85493 - 07/25/03 01:05 PM Re: ground rings
steve66 Offline
Member

Registered: 03/13/03
Posts: 25
The definition for a structure in article 100 is simply "that which is built or constructed." So couldn't a footing or column qualify as a structure? Then the ground ring would only have to encircle a footing, and not the entire building.

Article 100 also has a definition of a building; "A structure that stands alone or is cut off from adjoining structures...". The NEC handbook states that a "building" can also be a pole, a billboard sign, or a water tower.

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