Introduction to Grounding Basics
There are three main reasons for grounding in an off-grid power system: safety, voltage transients, and the sheer fact that they are required for some loads. But before we address each of these, it’s important to understand the actual definition of ‘ground’.
There are two types of ground: chassis (or mechanical) and electrical. Both are completely different grounds and must be understood correctly. ‘Ground’ is just a reference point; it does not always mean neutral.
Now with the definition nailed down, we will continue on with a deeper emphasis on electrical grounds!
A Few Things to Keep in Mind
- >> Ground Loops Should Be Avoided: The electrical ground should be connected to the system/earth ground at one point and only one point. Multiple grounds can cause the system and electrical equipment to function incorrectly. This is especially true with charge controllers, as ground loops can create additional paths for current to flow when the controller is trying to regulate.
- >> Connection to both a System Ground and Earth: An earth ground can be created by a ground rod, copper wire in the ground (known as a ground ring), and by other means. A mounting pole can be used as the ground, if installed correctly. However, an earth resistance meter should be used to measure the resistance from the system ground to the actual earth. It is recommended that the ground system have a resistance less than 5Ω to ground.
Note: Depending on the soil and site conditions, multiple ground rods may be required to achieve the required resistance.
- >> Different Grounds mean using an isolated DC/DC converter: Operating loads with different grounding requirements within the same system can be done using an isolated DC/DC converter. The load can still be grounded; the isolated DC/DC just allows the voltage to be inverted from other loads and systems as well. These types of converters are usually used to improve basic safety, enhance noise immunity, generate dual-polarity rails, and provide galvanic isolation and are used in a broad range of applications.
- >> Connection- Chassis and Electrical:
The connection from chasis grounds to the earth or system ground should be done by copper wire and ground lugs with bonding wires or self-tapping screws, as required. The electrical ground, on the other hand, can simply be made by connecting the grounded conductor to the earth or system ground. Refer to the National Electric Code (NEC) for grounding requirements.
Understanding the difference between a chassis ground and an electrical ground allows you to maintain an efficient and long-lasting system. While understanding exactly how much voltage is required in an electrical ground to offset the natural earth voltage is complex, when done correctly, it can prevent corrosion before it becomes visible. Grounding improves the safety in an off-grid system and allows the transient protection to function properly.