Ask ten renewable energy installers about system grounding and you’ll likely get ten different opinions as to what the National Electrical Code (NEC) requires, and what the correct methods are to meet those requirements.
After installing dozens of systems and teaching hundreds of classes about solar-electric (photovoltaic; PV) products and systems, I finally figured out the problem—grounding involves three different purposes and three major parts. If that weren’t bad enough, the same terms are often used when describing these multiple purposes and parts. No wonder people find grounding so confusing! But it doesn’t have to be that way. Here’s a simple guide to help you understand the basics of grounding.
The primary purpose of a grounding system is to reduce the risk of shock (and possible electrocution)—and there’s nothing confusing about why we want to do that. Electrocution or shock occurs when electricity flows through your body instead of through the normal electrical wiring system. Proper wiring and grounding will prevent this from occurring.
To protect against this risk, the standard, code-compliant practice is to connect all of the exposed metal parts of an electrical system together and then tie this system to the “ground” or earth. If two metal enclosures are electrically connected together with a wire, there will be no voltage difference (potential) between them. If the ground you are standing on is at the same voltage level as the metal enclosures, there won’t be a shock hazard if the enclosures become energized due to faulty wiring and you happen to touch them, since there will be no voltage difference to push the electricity through your body.
The second purpose of a grounding system is to provide a way to trip a circuit breaker if a ground fault in the system occurs. A “ground fault” occurs when the electricity flows through objects not intended to carry current, such as an enclosure or a person. When the system is properly grounded, the ground wires will provide an easy, low-resistance path for the fault currents, allowing high enough currents to trip a breaker.
Tripping the breaker reduces the risk of electrocution, protects the circuit’s electrical wiring from overheating (and possible fire) due to overcurrent conditions, and also makes it easier to identify the location of the hazard. The grounding system becomes a temporary path for the electric fault long enough to cause the circuit’s breaker to trip or fuse to blow. Having individual circuit breakers on each circuit in your home helps you or your electrician isolate the fault, find the problem, and fix it.
The third purpose of a grounding system is to reduce the potential for damage from lightning. Lightning can damage your renewable energy (RE) equipment or household appliances by forcing high currents and voltages through electrical equipment or causing arcs between a product’s electronic components that were not designed to handle these high-level voltages.
By providing a separate path for the flow of the lightning’s energy, and a way for it to dissipate back to the earth, sensitive electronics can be “shielded” from damage. Without a proper grounding system, your expensive inverter or charge controller can become the route for this energy, with unfortunate results.
All grounding systems can be divided into three different parts:
Too often these three parts get confused, the different terms are used interchangeably, or each part is just called “ground.” It’s much easier to discuss the topic of grounding if we use the proper terms for each part or function involved.