What is Minimum Grounding Resistance for Solar Arrays?

Grounding Standards for Solar Arrays

Grounding of solar arrays is critical to ensure safe and reliable operation. The IEEE 1547 and UL 1741 standards specify that the grounding resistance of a solar array should be 1 ohm or less. This ensures that any fault current can be safely diverted to ground without damaging the array or causing a fire hazard.

Measuring Grounding Resistance

Grounding resistance can be measured using a ground resistance test, which involves driving a current through the grounding system and measuring the resulting voltage drop. The grounding resistance is then calculated using Ohm’s Law (R = V/I). For example, if a current of 10A is driven through the grounding system and a voltage drop of 100mV is measured, the grounding resistance would be 10 ohms. However, this is not acceptable for a solar array. To achieve a grounding resistance of 1 ohm or less, it may be necessary to use multiple grounding rods or to increase the size of the grounding rod.

Techniques for Reducing Grounding Resistance

To reduce grounding resistance, it is essential to use a suitable grounding rod and to ensure that it is properly driven into the earth. The grounding rod should be at least 10 feet deep and have a diameter of at least 5/8 inch. In addition to using multiple grounding rods, it may be necessary to use a grounding plate or mat to increase the surface area of the grounding system. This can help to reduce the resistance of the grounding system and ensure that the solar array is safely grounded.