26 mm 2 (10 AWG) ground wire must be used, and in all other markets a 6 mm 2 must be used. There are several factors that make substation grounding absolutely necessary. Knowledge of the various types of system grounding and performance characteristics is critical when designing or operating an electrical system. Each DISTRIBUTION BOX and controller must be grounded. IN ELECTRICAL STATIONS INCLUDING TRANSMISSION AND DISTRIBUTION SUBSTAT GR THAN 8 FT FROM THE FENCE. THE FENCE SHALL BE GROUNDED SEPARATELY FROM THE GRID UNLESS OTHERWISE NOTED ON THE A PROPRIATE PROJECT DRAWING. 3 = Voltage tolerance is plus or minus 4% to 9%.