What it does—and where it belongs
An AC SPD complements PV-side protection. It diverts surge current to the bonding system and must be coordinated with upstream/downstream SPDs, backup protection and the building lightning protection design.
At the main distribution board, inverter AC board and sometimes sub-boards, depending on cable separation, lightning risk and coordination design.
What to check before you buy
Supply-system match
SPD connection mode and continuous operating voltage depend on the single/three-phase supply and earthing arrangement.
Protection level
Select a voltage protection level suitable for the inverter and downstream electronics, accounting for connection-lead voltage.
Backup protection
Check the maker's permitted fuse/breaker and prospective short-circuit current.
Coordinated locations
A main-board SPD can need another device near the inverter when conductor length or separation makes coordination necessary.
Red flags in a quotation or site visit
- A DC PV SPD is used on AC or vice versa
- Neutral/earth connection mode is guessed
- Long conductors are coiled inside the DB
- End-of-life indicator is hidden
Commissioning checks to request
Ask the installer to verify
- Connection leads are short and routed without large loops
- Backup protection matches the SPD instructions
- Status indication can be inspected
- Protective bonding path is continuous and appropriately routed
Common mistakes
- —Buying only by Imax
- —Putting all protection at one distant board
- —Ignoring lead length
- —Assuming an SPD protects against voltage that stays high for seconds or minutes
A better quotation line item
AC SPD Type ___ for ___ V, ___ phase, earthing arrangement ___, Uc ___ V, In ___ kA, Imax/Iimp ___ kA, Up ___ kV, backup protection ___, visual status and remote contact if required.
This wording is a procurement prompt, not a final engineering specification. Values must come from the approved single-line diagram and equipment manuals.
Standards and sources checked
Selection, installation and coordination principles for PV SPDs.
General principles for protection of structures, installations and people against lightning.
Requirements for power switchgear and controlgear assemblies, including PV-related annexes.
Pakistan project note: ask the installer to confirm the current PSQCA-adopted standard, inverter instructions, earthing rules and the latest DISCO/NEPRA interconnection requirements applicable to your site.
Questions about AC SPD
If I have a DC SPD, do I still need AC surge protection?
Often yes. The inverter is connected to both networks, and a transient can arrive or propagate on either side. Locations and types should come from one coordinated protection design.
Does an AC SPD fix high grid voltage?
No. SPDs address brief transients, not sustained voltage-quality problems. Persistent overvoltage needs utility/inverter protection investigation.