Grounding Impedance

[edavid]

What is a grounding impedance?

I have a project involving a 1500 kva, 4160-480y/277v, 3 phase, 4 wire substation. The planchecker is asking me to provide details, specifications and evidence of listing of a grounding impedance (watt, continues rating).

Please help.

 

[charlie b]

The neutral point of a transformer?s secondary can be connected to planet Earth (e.g., to a grounding electrode) either with a simple wire (the GEC) or via a grounding resistor. The purpose of a grounding resistor is to reduce the amount of fault current that would flow, in the event of a ground fault. This will allow the system to continue to operate during a ground fault, and is used when there is a significant reason to keeping the system on line. I have seldom seen it used, and have yet to include it in one of my designs. The question I would ask is whether your design has one or not.

The related requirements are in 250.36.

Welcome to the forum.