Surge protection device (SPD) showing a fault / end of life
A board-mounted surge protective device shows a fault indicator (window changed colour / flag) — it has likely reached end of life after absorbing surges and no longer protects.
Safety first
Isolate before replacing an SPD module. The board is live; treat as licensed work. A faulted SPD means downstream equipment is currently unprotected from surges.
Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.
Full detail — causes, the why, and common mistakes.
Likely causes
Ranked from most to least likely.
- 1
SPD module end of life (absorbed surges)
Most likelyThe MOV-based module has degraded after absorbing surges and indicates it needs replacement.
- 2
A large surge / event ended its life
#2A significant transient (storm/switching) took it out at once.
- 3
SPD disconnected / its protection operated
Least likelyThe SPD's own backup protection has operated, disconnecting it.
Reports are saved on this device to reflect what you actually find.
Testing sequence
Work through one test at a time. Expected reading and what each result means.
Check the SPD's status indicator/flag and any associated protection (its dedicated fuse/breaker).
A clear status: healthy, or end-of-life/disconnected.
If healthy, re-check the indicator interpretation.
End-of-life/fault indicated — plan module replacement.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
SPD fault indicated
→ step 2 - 2decision
Does the indicator show end-of-life / fault?
Yes→ step 3No→ step 4 - 3result
Replace the SPD module and restore its protection.
- 4result
Re-check the indicator interpretation.
Common mistakes apprentices make
- Ignoring an end-of-life SPD (leaving equipment unprotected).
- Not restoring the SPD's dedicated protection after replacement.
- Misreading the status window/flag.
- Replacing the module without isolating.
When to stop & escalate
SPD replacement is licensed work. Repeated short SPD life may indicate a surge-prone supply worth investigating. Until replaced, downstream equipment is unprotected.
If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.
Related faults
Switchboard buzzing, warm, or smells hot
The switchboard hums/buzzes, feels warm, or has a hot/burning smell — a sign of a loose connection or an overloaded device, and a genuine fire-risk warning.
Three-phase supply voltage high, low, or unbalanced
Measured supply voltages are out of the expected range or unbalanced between phases — causing equipment trips, poor performance, or protection operating across the board.
Loose connection overheating (discolouration / smell)
A terminal or connection is overheating — discoloured insulation, a burning smell, or heat you can feel — a common cause of nuisance faults and a real fire risk.
Learn the theory
How the gear and circuits behind this fault actually work.