Sizing main ground grid for 50% of the total design ground fault current conducted on the risers

[cuky2000]

Will be reasonable to design the main grid conductor for a fusing current of 50% of the design ground fault current?
This is because the fault conducted on the risers (pigtails)will split at least in two directions after reaching the main grid.
Please let us know if any industry reference or standard guideline in this matter.

 

[cuky2000]

FYI, enclosed are some information regarding this topic. Some colleagues are debating an split ratio 60/40, 70/30 but the enclosed information used by a large utility in US use 50/50.
Please let us know if any thoughts in this matter.

 

[waross]

Redundancy.
In the event of a failure of a ground grid conductor or grid connection, the current split may be lost.
I know from experience that some exothermic welds may be much less than perfect. There may be voids or porosity in the weld.
However, to maintain redundancy, rather than double the material cost of the grid, I would achieve redundancy by increasing the number of risers.
Alternatively the risers may be connected to the grid in two locations.
Any riser weld that is obviously defective may be abandoned and replaced.
While your group may reject the notion of redundancy, I suggest that it is an appropriate topic for discussion.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bacon4life]

The split will not be 50/50. The split of current between two parallel conductors of differing length and physical routing can be highly unequal. For example, the split would be closer to 30/70 in the attached image showing a fault on a pigtail close to a junction.