Grounding, bonding, and surge protection are three different jobs on a solar array. Grounding connects a system conductor, or an equipment part, to earth, in the way the electrical design requires. Bonding connects metal parts together so they stay at the same potential and so a fault has a path that can trip a breaker or a fuse. A surge protective device limits a transient voltage and diverts surge current. It does not ground the system, and a ground rod does not replace it. Mixing the three words is how a site ends up with a rod in the soil, loose module frames, and no protection on the conductors that actually see a surge.
What grounding and bonding are for
Equipment grounding and bonding give a fault somewhere to go so that metal you can touch does not sit at a dangerous voltage, and so the overcurrent device can open. Module frames, rails, and inverter cabinets are part of that metal. A painted joint or a loose lug is a break in the path. The drawing shows where the conductor lands. This page does not show a rod layout, a conductor size, or a depth. Those are calculations under the code the inspector uses, done by someone qualified. One country’s electrode rules are not another’s.
Array grounding also interacts with the inverter topology. A 2017 comparison of central and string inverters noted that transformerless, floating-ground string designs have to be checked against the module for potential-induced degradation. A grounded transformer scheme and a floating transformerless scheme are different. You do not “add a ground rod” to convert one into the other. The PID check is in what potential-induced degradation is. Large central inverters often include a transformer. Smaller inverters and microinverters are typically transformerless, in Pacific Northwest National Laboratory’s description. That is a topology fact, not a bonding diagram.
The DC equipment grounding conductor is not the grounded current-carrying conductor, when the design has one. People who land every green, white, and bare wire on the same convenient screw because they all “go to ground” create objectionable current and defeat fault clearing. If you cannot name which conductor is which on your inverter, stop and get the person who can. Live DC is not a place to learn the vocabulary.
What a surge protective device is for
IEC TR 63227:2020 describes a surge protective device as equipment that contains at least one non-linear component and that limits surge voltage and diverts surge current. Adding a conventional photovoltaic system to a building does not, by itself, change the risk that the building is struck. The technical report’s point is to design the lightning protection and the photovoltaic system together, before the array is up. A surge device on the DC lines is one piece of that design. It is not a lightning rod, and it is not a fuse. Fuse, isolator, and surge device stay different parts inside a combiner: what a solar combiner box is.
The device has a voltage rating that must match the circuit, including the cold open-circuit voltage of a PV string, and a current rating that is not a universal kiloampere number. This page does not recommend 20 kiloamperes or any other figure. A figure from a trade article is not a site design. The lightning article on this site stays at the same restraint: lightning protection for a solar array.
Surge devices can be damaged by a surge they diverted, and they can confuse an insulation test. NREL’s ground-fault field guide says not to megger casually, in part because surge devices can be harmed or can make the test lie. If a protector has a status window, read it. A failed protector is a short or an open, depending on the type, and leaving it in place “because the lights still work” leaves the next surge unaddressed. Replacement is a qualified-person job. The array is live in daylight.
How the three show up on a real array
| Part | The job | Not the job |
|---|---|---|
| Bonding jumper on the rails | Keeps frames and rails at the same potential and provides a fault path. | Does not stop a lightning surge. Does not set the inverter’s ground reference by itself. |
| Grounding electrode conductor | Connects the system’s grounding electrode as the design requires. | Does not replace bonding jumpers that were left off the modules. |
| Surge protective device | Limits surge voltage and diverts surge current, within its rating. | Does not clear a ground fault like a breaker, and does not isolate the array. |
A DC disconnect still isolates. A surge device does not. Shutdown remains the AC disconnect and then the DC disconnect, by a trained person. Those handles are in AC and DC disconnects for solar. Connectors are not a substitute for either the disconnect or the bond. A loose equipment-grounding lug in a connector box is a bonding failure you can sometimes see. Opening the connector to tug the lug, under load, is how that inspection becomes an arc. Connectors are in solar connector basics.
Ground-fault detection in the inverter is yet another function. It is the inverter noticing an unintended path to ground and stopping. It is not the green wire, and it is not the surge protector. When it trips, the response is a qualified person and the fault code, not a heavier ground rod. How weather and real faults get confused is in solar inverter faults and the weather.
Frequently asked questions
Is grounding the same as bonding?
No. Bonding ties metal parts together so a fault can clear and so touch voltage stays low. Grounding connects the system to the earth electrode the design specifies. You can bond a rail and still have a missing electrode, or drive a rod and still have unbonded frames. Both have to match the drawing.
Does a surge protector replace a lightning rod?
No. IEC TR 63227 treats the surge device as a limiter of surge voltage and a diverter of surge current. Lightning protection of the building is a separate design, done together with the photovoltaic system before the array is built. One device does not finish that design.
Can I add a ground rod to stop potential-induced degradation?
Not as a weekend fix. PID risk on a floating-ground transformerless inverter is checked against the module and the inverter topology. An extra rod is not that check, and it can create paths the original design did not have. Read the module manual and use someone who designs these systems.
Sources and references
A surge protective device limits surge voltage and diverts surge current; adding conventional PV does not by itself change strike risk; design the lightning protection and the PV together: IEC TR 63227:2020 preview. Do not casually megger; surge devices can be damaged or can confuse insulation tests: NREL ground-fault field guide. Transformerless versus transformer topologies, and PID as a module check: ICF, 2017 and Pacific Northwest National Laboratory. No rod layout and no surge current rating are given.
