Max Grounding-Grid Resistance for the GPR Screen (IEEE 80)
The inverse of the GPR screen: the grid resistance target that keeps the ground potential rise at or below the tolerable touch voltage, max_R_g = tolerable_touch / grid_current. A 200-V touch limit with a 200-A grid current needs a grid resistance of 1.0 ohm or less to clear the IEEE 80 screen without a full mesh/step study. IEEE Std 80 and a qualified grounding study govern.
Formula and source
max_grid_resistance_ohm = tolerable_touch_v / grid_current_a, the IEEE 80 GPR screen GPR = grid_current x grid_resistance solved for the resistance that keeps GPR at or below the tolerable touch voltage.
IEEE Std 80 ground potential rise, solved for the grid resistance, by name.
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