What is Grounding and Bonding?

Grounding and bonding are fundamental safety concepts in solar PV installations that every installer, technician, and system owner should understand. Though these terms are frequently confused or used interchangeably, understanding their distinct roles is crucial for electrical safety. Grounding creates a connection to the physical earth, providing a reference point of zero volts and protecting against voltage fluctuations from lightning or other electrical disturbances. Bonding, on the other hand, ensures all metallic components are electrically connected together, preventing dangerous voltage differences between metal parts that could create shock hazards for anyone working on or around the system.

Understanding the why behind these safety practices is just as important as knowing how to implement them correctly. Proper grounding and bonding not only protect personnel from electrical hazards but also ensure that protective devices operate effectively when needed. In the video below, instructor Rebekah Hren explains these fundamental concepts at the start of the much more advanced Solar PV Ground-fault Troubleshooting: Theory, Tools, and Field Application course. This comprehensive training program goes far beyond the basics, covering real-world scenarios and advanced diagnostic techniques essential for safe and effective PV system maintenance.

Transcript below.

 Grounding, I think, is pretty intuitive. It means connected to the earth. You can see in the image on the screen that we’ve got our soil, the earth, the ground, as we call it, and we have a connection to ground. 

We have a grounding electrode. We’re showing a ground rod. There are a lot of different electrode types that you’ll see on sites. Ground rings around the concrete pad are very common. Ground plates, concrete-encased electrodes, rebar and concrete – those are all designed to have a low- resistance connection to the physical earth. 

We also have a grounding electrode conductor, the GEC. That is the wire that’s connecting our electrical system to the electrode and to the ground. 

On PV sites, we also have a lot of metal parts and pieces that have to be bonded together to establish that electrical continuity and electrical conductivity. Equipment bonding and grounding can be a lot of different things. Here we’re pointing to a connection between the metal module frame and a rail. We have to bond the metal parts of our rack together.

We also have equipment grounding conductors. The green insulated conductors or bare copper wires that you see on sites. If we have metal conduit, it has to be bonded. Here we’re showing an equipment grounding conductor running through the conduit. We’ve got terminal strips and enclosures. All of that metal has to be bonded together. 

 Why bond? Well, I think it’s fairly intuitive and easy to understand. Bonding ensures that all the conductive parts are connected together and to the grounding system. The big benefit of bonding is that it prevents differences in potential between metallic parts of a system. 

What does that really mean?

Well, if I’m standing on a site and I have a piece of metal racking to my left and a piece of metal racking to my right and they aren’t bonded together, then there could be a potential difference between those two pieces of metal. And potential difference is the same as voltage and voltage causes a current to flow.

So if I touch both of those pieces of metal at the same time, very small amounts of current can kill you. By bonding those two pieces of metal together, we’re making sure that we don’t have current flowing where we don’t want it to flow. The conductive parts are bonded to ground, which means they have zero volts with reference to ground. And earth is always at zero volts.

So no matter what kind of faults are happening in a system, what kind of miswiring might have occurred, we can rely on the fact that the earth, and anything bonded to the earth, is going to remain at zero volts. 

Also, really critically, that bonding creates an effective fault current path, which we’re going to talk more about in just a minute. But that effective fault current path is what ensures that our ground fault protection is going to operate and that our over current protective devices are going to operate.