We have a 480V power supply located on an Aluminum walkway. We have it grounded to the walkway, which is about 20 feet off the ground on steel columns into concrete. Is these grounding sufficient for the application?
Please describe in detail what you mean by "480 volt power supply".
Is this the secondary side of a step down transformer feeding a main panel?
Is this a 480 volt sub-panel, fed from a larger 480 volt panel at a different location?
Your description would indicate that this power supply is probably bonded to the walkway. There is not enough information to assume that it is grounded.
If this a seperatly derived system (SDS)per NEC 250.30, then the transformer has to have a grounding electrode, per 250.50. Typically a driven electrode will suffice. The SDS will need a main bonding jumper in the transformer or first disconnecting means
[ February 27, 2003, 10:00 AM: Message edited by: tom baker ]
Section 250.4(B) of the 2002 NEC covers grounding of non-current conductive components of and electrical installation. The electrical system is not required to be grounded, but the mechanical components are. The equipment must be connected to earth. I will assume that the steel support for the walkway is in a concrete footing, so a bonding conductor from the transformer enclosure to the steel support should be sufficient.