earthing

http://cr4.globalspec.com/thread/15278/earth-pit-electrod-resistance-value

hi....i am not in the earthing business. All i need to know is when client comes to buy copper for earthing. i need to sell him ready made copper rectangular sheets for earthing. I want to give him the value that for this cross sectional area what would the maximum earth fault current it can handle?..what is the formula for working that cross sectional area for that fault current?...not for rod or strip but for copper mat(mesh)...

Roger

Why would you use a coper sheet rather than a ground rod?

it is easy to manufacture copper sheets than copper rods. we are searching the possibility of providing a new form of copper sheets for earthings. having just slits thorugh the middle and then expanding this sheet of copper. so the cable will run through the expanded slits. but i need to know the cross sectional area required for the earthing normal house. i can use presume a fault current of 6kA for normal house.but how can i calculate the cross sectional area of the copper sheet.?

Earth mat are of various sizes depending on ones design spesification and expected fault current. Most often, we exceed the desired capacity consciously to give room for inefficiency. In several other places earth mat and copper rods (or a rod) are used for domestic earthing and are bonded together to further enhance efficiency.

By calculating the total earth electrode resistance value, u can have a picture of ur expected fault current to be desipated by the earth mat. The more the area of the mat, the quicker and better for u. Earth mats for residential buildings are usually half a meter square and buried buried 4ft deep. A 20mm² or 25 mm² 4ft or 5ft length Copper rod in most cases are bonded to the mat and buried together.

The copper tape is of various sizes, the standerd for earthing is 25mm x 5mm.

Dickson, Abuja, Nigeria.

hi

thank you for the reply

the area for that you specified of half a meter will this be sufficient for a residential building that normally has 6kA fault current. also what would be the cross sectional area of the cable that we would run through?..i said 35mm2 would be sufficient since it needs only 1 sec capability.0 heat. correct me if im wrong.

please

Half a meter² of copper tape will be OK for the transient earth fault current. NOTE: In large domestic and commercial buildings, there are three diffrent earth pits required as follows: Normal electrical earth pit, thunder/Lightening arrestor earth pit and communication earth pit. It is better to have them separately than bonding them together. If ur case is that of a residential building only, the specification u have is OK.

Dickson.

Hi All

I am busy with the earthing design of a 60m telecommunication tower. I am using copper for the entire earthing. The area is 19x13m. the tower has 3 foot foundations of 3.8x3.8. I have assumed earth resistance of 2ohm and soil resistivity of 100ohm/m. The ps i have assumed as 3000ohm/m. I have assumed the fault current to be 45kA and duration of fault of 1sec. The time duration for estep and etouch as 0.5sec. I would like to calculate the tolerable step,touch voltage and ground rise potential. I also need to calculate the size of the earth mat and the earth rod size. I am getting bogged down with the formulae regarding the sizing of earth mat since there is tons of formulae for earthing. I calculate a value for estep and etouch but what is the permissible values? once I have sized the earth mat my doubt is how do i design the grid pattern once sizing it and also need to know whether the cross sectional area of each joint(grid pattern) is sufficiently sized to withstand the current.