Wire Size For Transformer Ground

[pdemapan]

I have a new pad mounted 75 kva transformer (13.8 KV - 480Y/277V 3PH, 4W). The transformer needs to be grounded but I was unsure about the size of the grounding conductor. The conductors for the secondary side of the transformer are sized as 1/0 copper. Looking at Table 250.66 it seems that I can size the ground conductor as small as #6 copper. According to Table 310.16 the ampacity of #6 is 65 amps but on the seconary size, the transformer will draw (75000kva)/(480V)(1.73) = 90.32 amps at full load. Is this the proper way to size the ground or should I go one cable size larger? I would appreciate any help as always. Thank you, patrick

 

[LISHAJI]

NEC 250.24(c)(1) Indicates that the grounding shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but
shall not be required to be larger than the largest ungrounded
service-entrance phase conductor.

Thus the ground electrode has to based on the largest ungrounded phase conductor.

 

[pdemapan]

NEC 250.24(c)(1) Indicates that the grounding shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but
shall not be required to be larger than the largest ungrounded
service-entrance phase conductor.

Thus the ground electrode has to based on the largest ungrounded phase conductor.

The largest ungrounded phase conductor on the secondary side is 1/0. Therefore can I assume that #6 ground will be a sufficient size ground based on Table 250.66 NEC and as per NEC 250.24(c)(1)?

 

[Mike01]

multiple conductors

multiple conductors

?? if you have multiple sets of conductors over 1100kcmil say 6 sets of 600's that would be a total of 3,600,000 mills then 12.5% of that is 450,000cmills (rounded up to 500kcmil) so this would be the total area required do you then divide that by 6 (the total number of paralleled sets) to get a minimum of 75,000 cmill conductor per phase for the parallelled sets to get the sum of 500,000??