gulkhan123
Member
Q: The recommended size of Ground Loop Conductor buried around a building is usually 95-120sq.mm with 7-8 no.of ground rods bonded to it. I wonder how do they calculate this size and the number of ground rods? Thanks. gk
Ground Loop Around Building
- Thread starter gulkhan123
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You said recommended, recommended by whom? By the NEC a ground ring does not need connection to ground rods.
iceworm
Curmudgeon still using printed IEEE Color Books
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Since you are using "sq mm" wire, I guessing you are not in the US. What code are you working to?
ice
brian john
Senior Member
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Here it is based on the size of the building and what they read in past specifications, in another words a WAG (Wild As* Guess) with little or no engineering. And in 99.9% of the jobs where we had to test these large ground rings the WAG worked as it resulted in a low resistance ground.
Julius Right
Senior Member
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- Electrical Engineer Power Station Physical Design Retired
According IEEE Std 80/2000
ch. 11.3.3 Additional conductor sizing factors
"In practice, the requirements on mechanical reliability will set the minimum conductor size. While it might seem proper for the designer to establish minimum sizes in light of local conditions, the need for conservatism deserves consideration."
4/0 awg [or 95 sqr.mm ] will be -from mechanical and corrosion point of view- an acceptable cross-section for stranded copper conductor [as a minimum if short-circuit conditions will required less].
Number of electrodes-if any required-depends on GPR level required. However, a minimum of 5-7 m distance between could be recommended.
ch. 11.3.3 Additional conductor sizing factors
"In practice, the requirements on mechanical reliability will set the minimum conductor size. While it might seem proper for the designer to establish minimum sizes in light of local conditions, the need for conservatism deserves consideration."
4/0 awg [or 95 sqr.mm ] will be -from mechanical and corrosion point of view- an acceptable cross-section for stranded copper conductor [as a minimum if short-circuit conditions will required less].
Number of electrodes-if any required-depends on GPR level required. However, a minimum of 5-7 m distance between could be recommended.
- Location
- Illinois
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- retired electrician
That is a substation grounding standard and would not really apply to the original question.
gulkhan123
Member
The size 95-120 sq.mm corresponds to 4/0 AWG. Will appreciate ur feed back. thanx
gulkhan123
Member
Most project specification requires and as I understand ground rods are usually bonded to the loop around the building. Further it says-" you may add more rods in order to achieve the required ground resistance" say less than 5 ohms, similar to a loop around a substation where at least one rod is buried at each corner, attcahed to the loop.
Will await your response. thanx
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iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
Well, I suggest you read IEEE 142 on grounding industrial systems. That will tell you about ground rods. And Julius gave you a good reference on the loop conductor sizing.
Without knowing the codes and standards you are working under, that's all the help i have.
ice
- Location
- Lockport, IL
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- Retired Electrical Engineer
What I gleaned from the responses above is probably the same thing I would have said. This is not something that you determine using calculations. There is no formula that will tell you a minimum size for the wire that surrounds the building, nor the number or spacing of ground rods. There are, however, software packages that can calculate the ground resistance that will be obtained in a given environment and with a given grounding electrode system. The one I have on my company's network is called "Ground Mat," a product of the SKM company. There are others as well. But keep in mind that these programs will calculate the result of a GES design, and will not calculate the required sizes of any GES component.
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