De acordo com a Tabela 250.122 do National Electrical Code, um condutor de cobre 10 AWG é bom como um condutor de aterramento de equipamentos para circuitos com proteção de até 60 amperes.
National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 250 Grounding and Bonding
250.122 Size of Equipment Grounding Conductors.
(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4). Equipment grounding conductors shall be permitted to be sectioned within a multiconductor cable, provided the combined circular mil area complies with Table 250.122.