Quick Answer
Using a common ground for AC and DC systems is generally safe if done correctly and following proper safety guidelines, such as ensuring that the DC grounding point is isolated from the AC system and not creating a path for current to flow from the AC system to the DC system.
Safety Considerations
When designing a solar system, it’s essential to separate AC and DC grounding to prevent electrical shock and damage to the system. A common mistake is to use the DC negative bus bar as the grounding point for the AC system, which can create a hazardous situation. To avoid this, consider using a dedicated grounding point for the AC system, such as a grounding rod or a grounding electrode.
Correct Grounding Practices
The National Electric Code (NEC) recommends using a separate grounding electrode for AC and DC systems. For a typical residential solar system, a grounding electrode with a resistance of 10 ohms or less is recommended. To ensure proper grounding, connect the grounding electrode to the AC panel’s grounding bus bar and to the DC system’s grounding point. It’s also crucial to verify that the grounding point is properly bonded to the equipment grounding point to prevent electrical shock.
Bonding and Isolation
To prevent electrical shock and ensure safe operation, it’s essential to bond the AC and DC grounding points together. The bonding jumper should be sized according to the NEC and should not exceed 6 AWG. Additionally, ensure that the DC grounding point is isolated from the AC system, and a clear path is maintained for fault current to flow from the AC system to ground. This can be achieved by using a DC isolation device or a DC grounding transformer.
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