Resistance Grounded

[chadwiseman]

How would one select the appropriate size resistor for a LV system. We are trying to select between 100 and 200 ohm to limit the ground fault. Is there any guidance out there for this?

 

[alehman]

For high resistance ground (which appears to be what you are trying to do) you want the fault current to exceed the capacitive charging current - usually between 1 and 10 amps.

http://www.postglover.com/products/grounds/keeper.htm

 

[raisinbran]

86ranger
In the coal mining industry, all three phase systems used underground are resistance grounded. MSHA (Mining Safety and Health Administration) criteria is to limit the maximum voltage that can appear on the frame of a piece of equipment during a ground fault to 100 volts. All of the equipment is connected to its source through cables - some of which are very long. With the 100 volt criteria, and knowing the resistance (impedance) of the grounding conductor, you can determine an appropriate grounding resistor. Typically, in the mines, it is 15 amperes on 480, 575 and 995 volt equipment, and either 15 or 25 amperes on high voltage distributuion systems. Typically they are 4160, 7200, 12470 or 13800 volt.
Hope this helps,
Raisinbran