size of grounding conductor for a circuit that is tapped from a transformer secondary

[electricalMike]

Can someone tell me what the NEC has to say for the sizing of a grounding conductor for a circuit than is tapped off of a transformer secondary. The overcurrent protection is on the primary side of the transformer.
Thanks in advance!

 

[augie47]

With utility owned transformers supplying services, there is normally no "grounding" conductor as the grounded conductor usually serves as the "ground" until you reach the service disconnect.
On Separately Derived Systems (non utility) the "grounding" is covered by NEC 250.30.
The system bonding jumper is sized per 250.28 which normally is sized per 250.66 and the equipment bonding jumper is sized per 250.102(C) which again references 250.66 until your phase conductors exceed 1100 kcmil cu