Sizing Grounding Electrode for a 300 KVA transformer

[Coreyd1@optonline.net]

Feeding a 480v delta/Y 300 KVA transformer with two sets of 4/0. The secondary side will 3 sets of 400KCMIL.

When sizing the grounding electrode to be attached to building steel Should I use the primary or secondary side conductors and should the conductors area be added together to size the grounding electrode using table 8 chapter 9 per table 250.66 Note 1.

 

[texie]

Feeding a 480v delta/Y 300 KVA transformer with two sets of 4/0. The secondary side will 3 sets of 400KCMIL.

When sizing the grounding electrode to be attached to building steel Should I use the primary or secondary side conductors and should the conductors area be added together to size the grounding electrode using table 8 chapter 9 per table 250.66 Note 1.

You use the sum total of the secondary conductors. In your case this will be 1200 KCMIL. You don't say if this is CU or AL.
Assuming CU, table 250.66 would indicate a 3/0 CU or 250 AL. Keep in mind that GEC's max out at some point as seen in the table and text. Also important is that while GEC's max out, bonding jumpers do not.

 

[Coreyd1@optonline.net]

Using copper its a 300 kva K4 transformer

 

[infinity]

Once you exceed 1100 kcmil the largest required GEC is #3/0. {T250.66} You system bonding jumper would be based on 12.5% of the total CM area of the secondary conductors.

 

[kwired]

Size of conductors on the separately derived system is all that matters. Transformer kVA is meaningless to T250.66.

You could have same conductors run to only a 15 kVA transformer and the GEC would still have to be the same size, and you would also have a very crowded termination area in the transformer