Quick Answer
The NEC (National Electric Code) requires grounding wire sizes based on the ampacity of the service, feeder, or branch circuit they are protecting. For a single-phase 120/240-volt service, grounding wire sizes are typically 6 AWG or larger, but can be smaller for smaller services. The NEC also requires a minimum of 1/0 AWG grounding wire for ground fault protection.
Grounding Wire Size Requirements
The NEC requires grounding wire sizes to be sized based on the ampacity of the service, feeder, or branch circuit they are protecting. For example, a 200-amp service with a three-phase 208-240-volt configuration requires a minimum of 4/0 AWG grounding wire according to NEC Table 250.66. This is also true for ground fault protection systems, where a minimum of 1/0 AWG grounding wire is required according to NEC 430.36.
Bonding Requirements for Solar Grounding Systems
Bonding requirements for solar grounding systems are critical to ensure safe operation and prevent electrical shock. NEC 250.104 requires equipment grounding conductors to be bonded to the grounding electrode conductor at the service equipment, but for isolated ground systems, the bonding is typically done at the inverter or charge controller. This involves connecting the grounding wire from the system to the grounding electrode through a bonding jumper, usually a 1/0 AWG or 2 AWG wire, depending on the system size and configuration.
Grounding Wire Size Calculations
When sizing grounding wire for a solar system, it’s essential to calculate the maximum fault current that could flow through the system. This can be done using NEC Tables 250.122 and 250.66, which provide ground fault currents for different types of circuits and equipment. For example, a 200-amp 240-volt inverter requires a minimum of 4/0 AWG grounding wire if the ground fault current is 30,000 amps or greater, according to NEC Table 250.122.
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