Surge protection for PV systems is often sold as lightning protection, which is a different product doing a different job. A surge protective device clamps a fast overvoltage and diverts the energy into the bonded metal of the system. It does not intercept a strike, does not guarantee survival of a direct hit, and does essentially nothing if the bonding it relies on is incomplete. It is one layer in a scheme, not a shield.
What a surge actually is
Most damaging surges on a photovoltaic system are not direct strikes. They are induced events. A lightning discharge a few hundred yards away couples energy into the long conductor loops formed by string wiring, communication cables and the alternating-current feeders, producing a brief but very high voltage spike. Utility switching operations, nearby faults and large motor loads produce smaller versions of the same thing. The spike lasts microseconds, far too short for any fuse or breaker to respond, and it arrives as a voltage far above what the semiconductors in an inverter or module-level device can tolerate. A surge protective device conducts heavily above a threshold voltage, clamping the spike and dumping the energy into the bonded metal path, then returns to a non-conducting state.
Why placement matters more than rating
A surge device protects what is close to it. The connecting leads between the device and the conductors it protects have inductance, and a fast-rising surge develops significant voltage across even a short lead. That means long, looping connections between the protective device and the equipment badly undermine the protection, regardless of how impressive the device’s ratings are. Effective installations keep the leads short and straight, place devices at the points where surges enter, and use more than one device where the system has several exposure points. On a typical photovoltaic system that means protection on the alternating-current side near the service, protection on the direct-current side near the inverter, and often another near the array on a long ground-mount run.
Everything depends on the bonding
A surge device works by moving energy somewhere. That somewhere is the bonded metal of the system, which must be continuous and connected back to the grounding system. If a rail section is unbonded, a bonding jumper was omitted, or a connection has corroded, the diverted energy has no good path and will find a bad one, often through the very equipment you were protecting. This is why surge protection and bonding are not separate topics. Adding surge devices to a poorly bonded array is close to pointless. Verifying bonding continuity at commissioning is the prerequisite, and re-verifying it after any roof work is how you keep the protection real.
Devices wear out and stop telling you
Most surge protective devices use components that degrade with each event they absorb. After enough energy has passed through, the device stops clamping effectively, and in some designs it fails in a way that is not obvious from outside. Good devices include a status indicator, a window showing green or red, or a remote contact that the monitoring system can read. Owners rarely look. A device that failed during a storm three summers ago has been protecting nothing since. Checking the indicator should be on the same maintenance visit as the thermal scan, and a device that has tripped its indicator needs replacement by a qualified person, since it sits on energized circuits.
What real lightning protection would involve
Intercepting a strike is a separate discipline involving air terminals, dedicated down conductors sized for the current, and a grounding electrode system designed for the purpose. It is engineered against dedicated standards, it is expensive, and it is usually justified only for tall exposed structures, high-value facilities or sites in regions with severe lightning activity. A residential rooftop array in an average location is normally protected adequately by good bonding plus surge devices, accepting that an extremely close strike can still cause damage. Being clear about which product you are buying prevents the disappointment of discovering after a storm that the surge device was never meant to stop what happened.
What to check before you act
- Confirm bonding continuity was tested before relying on surge devices.
- Ask where devices are installed and how short the connecting leads are.
- Check the device status indicator during routine maintenance.
- Understand that surge devices are not lightning interception systems.
Common questions
Does my inverter already include surge protection?
Many do include some internal protection, and the manual will say what and where. Internal protection is usually a supplement to external devices rather than a replacement for them.
Will surge protection save my array from a direct strike?
No. A direct strike delivers energy far beyond what these devices are rated to divert. They protect against induced surges, which are the far more common cause of damage.
The practical takeaway
Verify the bonding first, then place surge devices close to the equipment with short leads, then check their indicators periodically. If your site genuinely warrants strike interception, that is a separate engineered system. All device installation and replacement is qualified-installer work.
References and further reading
- NFPA: the National Electrical Code, including surge protection and bonding provisions
- NFPA: electrical safety research and education resources
- NREL: photovoltaics research including system reliability and balance-of-system components
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
