17/09/2026
⚡ “Lightning Grounding Must Be Separate from Building Grounding.”
Really?
This statement is still commonly heard in engineering discussions.
But before accepting it as a rule, we should ask a more important question:
Separate physically — or electrically?
These are NOT necessarily the same thing.
The philosophy of IEC 62305 focuses strongly on equipotential bonding and controlling dangerous potential differences during a lightning event.
A lightning strike can involve extremely high currents. The objective of the earthing and bonding system is therefore not simply:
❌ “Make the lightning earth separate.”
or
❌ “Achieve the lowest possible earth resistance.”
The real objective is:
✅ Provide a suitable path for lightning current.
✅ Minimize dangerous potential differences.
✅ Reduce the risk of side flashing.
✅ Establish appropriate equipotential bonding.
✅ Protect electrical and electronic systems through proper bonding and SPDs.
Consider this scenario:
LPS Earth → completely isolated
Building Earth → completely isolated
Both systems have excellent earth resistance.
Sounds good?
Not necessarily.
During a lightning event, the potential of the two earth systems can rise differently. That potential difference may create an unintended current path through building structures, cables, metallic services, or equipment.
So perhaps the better question is not:
“Should lightning grounding be separated from building grounding?”
but:
“How should the earthing systems be interconnected and bonded to safely manage lightning current and potential differences?”
This is where IEC 62305-3 and IEC 62305-4 become important.
Another common misconception:
“Separate grounding = safer grounding.”
Not automatically.
And:
“Low earth resistance = good lightning protection.”
Also, not automatically.
Lightning protection is a system, not just an earth rod.
Air termination + down conductors + earth termination + bonding + separation distance + SPDs + proper routing must be considered together.
💡 Engineering is sometimes less about following a simple rule and more about understanding why the rule exists.
So, what's your opinion?
Should LPS earthing and building earthing be completely isolated, or should they be bonded as part of an equipotential system?
Let's discuss.
📚 Reference: IEC 62305 Series – Protection against lightning
• IEC 62305-3 – Physical damage to structures and life hazard
• IEC 62305-4 – Electrical and electronic systems within structures
