Grounding in PV systems: what each connection is for

· 6 min read ·

What each earth connection does in a solar system: structure, inverter, SPDs and busbar. A guide to concepts; exact rules come from the local standard.

What grounding is for

Earthing a PV system is not a single connection, but a set of connections with different purposes. This article explains the concepts. The exact requirements (cable sizes, resistance values, electrode type and rules for the DC side) depend on your country’s standard and on the equipment, and must be defined by a qualified professional.

Protection against shock

If something fails, the current finds a safe path

  • Connects the metal parts to earth
  • Lets the protection act on a fault
  • Reduces the risk of voltage on the enclosure

Equipotential bonding

Reduces voltage differences between the parts

  • Joins structure, frames and enclosures together
  • Avoids voltage differences between metal parts
  • Helps the protections operate

Surges and lightning

A path for the excess energy

  • SPDs divert the surge to earth
  • They only work with good earthing
  • They do not replace a lightning protection system, where required
Each earth connection serves one of these three functions.

Each connection and what it does

Tap each device to see what it does. In the diagram, the earth connections all reach the same earthing system.

Interactive

Where does each earth connection go?

Tap a device to read the role of its earth connection. SPDs are connected in shunt, between the conductor and earth.

DC side (direct current)AC side (alternating current)Earthing

Structure, inverter, board and SPDs all end at the earth busbar, which goes to the earth electrode.

Structure and frames

equipotential bonding

Connects the metal parts of the panels and the structure to each other and to earth, to reduce the risk of a part being energized by mistake.

Where it goes: from the structure to the earth busbar

Inverter protective earth

PE

The earth terminal of the inverter’s enclosure. It lets the protection act if there is a fault to the enclosure.

Where it goes: from the inverter to the earth busbar

Board earth

PE

The protective conductor that runs with the AC circuits and connects the board to the installation’s earthing system.

Where it goes: from the board to the earth busbar

SPD: diversion to earth

surges

The surge protective device connects the conductor to earth when an overvoltage appears. The cable to earth should be short and direct.

Where it goes: in shunt, next to the inverter or the board

Earth electrode

earth

The point where the installation meets the ground. The type, the depth and the acceptable resistance follow the local standard.

Where it goes: in the ground, connected to the main busbar

The path to earth

In practice the drawing usually follows the same logic: each metal mass goes out to a common busbar and from there to earth.

  1. 1
    Identify the metal parts

    Structure, panel frames, inverter enclosure, boards and metal conduits.

  2. 2
    Connect everything to the earth busbar

    In general, each part is connected to the busbar by its own conductor, without depending on another to keep continuity; the exact arrangement follows the design and the standard.

  3. 3
    Connect the busbar to the electrode

    The busbar goes on to the installation’s earthing system, according to the standard and the design.

  4. 4
    Verify and document

    Continuity and earthing should be measured and recorded by a qualified professional, at installation and periodically afterwards.

What tends to go wrong

Do

  • Use connectors and lugs suited to the structure and the type of metal
  • Keep the SPD cable short and free of sharp bends
  • Follow the inverter manual on the earth terminal
  • Leave measurements and documentation to a qualified professional

Avoid

  • Rely only on the structure to carry the current to earth
  • Mix metals that corrode in contact, without treatment
  • Make loose splices or ones unprotected from the weather
  • Copy values from another installation or another country

On standards and responsibility

  • Ask the installer which standard was used and ask for the measurement records
  • Confirm there is equipotential bonding between the structure, the inverter and the board
  • Check that the SPDs are connected to earth with short cables
  • Ask for periodic review of the earthing, especially in areas with a lot of lightning

Draw it in Editor Solar

This is Editor Solar itself, already loaded with the diagram from this article. Move the equipment, edit labels, connect new parts and export to PNG, SVG or PDF. It is free and runs right in your browser.

Panel structure, inverter, SPDs and board connected to the same earth busbar, which goes to the earth electrode.

Try it: Add a second panel structure to the drawing and connect it to the same earth busbar. Note where the earthing junction box would go.

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Open this diagram in the full editor ↗

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