Grounding grid and low voltage transformers 1

[lume7006]

Dear guys,

I come to you asking for some advice in order to get some technical references that may help us explain/understand the following:

When we have a grounding grid, we evaluate it from the standpoint of step and touch voltages considering the single phase to ground at the PCC because the rest of the facilities (medium and low volages like 13.8, 4.16 and 0.48 kV) are according to the NEC.

Our grounding grid is design in such a way that the main subsation (PCC) has a grid and every electrical room has another grid and all of them are interconnected.
However, we do not evaluate its performance for single line to ground faults at low voltage because of the above mentioned and also because at 480 V the result may tell us that a 5 kV step voltage is rised, which cannot be true.

Any suggestions, mainly technical papers and references will be welcome.

 

[rcw retired EE]

I believe you have the correct interpretation.

At low voltage, the equipment grounding conductors control step and touch voltages.

Check the IEEE Green Book - ANSI/IEEE Standard 142.

 

[memos1006]

I think you should read NEC and IEE Green book