TRANSFORMER SECONDARY BOND

[ohmhead]

Question secondary bond to neutral per NEC art 250 would you use table 250.66 to size this bonding jumper to neutral to building steel .
If the transformer had paralleled feeders would you use 250.100 (c) 12 1/2 percent of the largest feeder and bond to building steel .

Which rule would be the correct one to solve this question .

 

[infinity]

For the GEC to building steel you would use 250.66 for any size secondary conductors. #3/0 is the largest size that's required. For the system bonding jumper you would also use 250.66 untill you got to parallel conductors that were greater than the sizes listed in that table, then you would use the 12.5% rule.

 

[ohmhead]

Question secondary bond to neutral per NEC art 250 would you use table 250.66 to size this bonding jumper to neutral to building steel .
If the transformer had paralleled feeders would you use 250.100 (c) 12 1/2 percent of the largest feeder and bond to building steel .

Which rule would be the correct one to solve this question .

Thanks the issue is the oneline shows a 3/0 to building steel i have a 500 kva transformer with 6 runs of 600 mcm alu conductors

we have 12 of these transformers to connect so the big question is do i use a 3/0 copper or a 500 mcm at 12 %.

It appears to be going to be a 500 mcm if the table is smaller then the 12 percent of the 600 mcm .

Thank you for the help .