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Section 32 · Rules

Grounding and lightning protection for solar pumps

A solar pump is often the tallest metal object in a pasture, connected by a long cable to a steel well casing that goes down into the water table. That is a fine path for a nearby strike, and the controller sits in the middle of it.

By the editors of SolarPoweredWaterPumps.comLast reviewed October 20262 min read

Short answerBond the array frames, mount and controller to an equipment grounding conductor and a grounding electrode as NEC Article 690 and the pump maker require, and add surge protection on the long DC run between array and controller. Lightning damage to remote pump controllers is common and mostly preventable.

Key takeaways

  • Bond array frames, mount and controller to an equipment ground and an electrode.
  • Add a DC-rated surge protector at the controller on long runs.
  • Follow NEC Article 690 and the controller manual; use a licensed electrician where required.

What has to be grounded

Follow the manual and the code
Grounding details vary with the system and the code edition your jurisdiction uses. Follow the controller manufacturer's instructions and NEC Article 690, and use a licensed electrician where your state requires one.
  • Module frames and the mount, bonded together and to an equipment grounding conductor run with the circuit conductors.
  • The controller enclosure, to the same equipment ground.
  • A grounding electrode, typically a driven rod, as the pump maker's manual and NEC Article 690 require. A metal well casing may serve as or be bonded to the electrode system where code allows.
  • The pump motor, through the ground conductor in the drop cable, where the motor provides one.

Surge protection

Long DC runs pick up induced surges from strikes that never hit the array. A surge protective device rated for the DC voltage, fitted at the controller end and grounded with a short, straight lead, absorbs much of it. Some pump controllers include protection; others leave it to the installer. Ask before buying.

Layout that reduces damage

  • Keep array-to-controller and controller-to-pump runs as short as practical, and run conductors of a circuit together rather than in separate trenches.
  • Bury cable in conduit where practical.
  • Fit a disconnect so the array can be isolated before working on the pump.
  • After a storm, check the controller's indicator lights first. It is the most common casualty.

Questions

Does a solar well pump need a ground rod?
Usually, yes. Most pump controller manuals and NEC Article 690 call for the array, mount and controller to be bonded to an equipment ground and connected to a grounding electrode, commonly a driven rod. Follow the maker's instructions and local code.
Next step

Voltage drop distances for 12V, 24V and 48V-class pumps on each gauge.

Size the wire
Sources
  1. NFPA 70, National Electrical Code (Article 690 covers solar PV systems; Chapter 9 Table 8 gives conductor resistance)