Light bulbs keep blowing in the same fitting
One fitting eats lamps — sometimes weekly — while the rest of the house is fine. The lamp isn't the problem; something about that fitting or its supply is.
Safety first
Isolate and prove dead before touching the lampholder or its terminations — a fitting that's been arcing may have damaged insulation and heat-affected conductors.
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.
Apprentice mode
Full walk-through — the why, what readings mean, mistakes & safety.
Likely causes
Ranked from most to least likely.
- 1
Loose or arcing connection at the lampholder or its termination
Most likelyA pitted centre contact or loose terminal arcs on every switch-on. The voltage spikes and heat kill lamps early — and it's a fire risk in its own right.
- 2
Heat build-up in an enclosed or covered fitting
#2A lamp over its rated wattage, a sealed/enclosed fitting, or ceiling insulation packed over a downlight cooks the lamp (and the fitting).
- 3
Vibration at the fitting
#3Fittings under a floor with foot traffic, near a slamming door, or on a fan/garage door track shake filament and cheap LED driver lamps to death.
- 4
Sustained high supply voltage
#4Premises close to the transformer or at the top of a stiff network can sit high. Sustained voltage near the top of (or above) the allowed range shortens lamp life dramatically — every fitting suffers, but the most-used one fails first.
- 5
Cheap or wrong lamps
Least likelyBargain-bin lamps, or the wrong type for an enclosed/dimmed fitting (many LEDs aren't rated for either), fail early and get blamed on the wiring.
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.
On the tools? Job Mode shows one test at a time with thumb-sized buttons — your place and readings carry straight over.
Enter Job ModeIsolate, prove dead, and inspect the lampholder: look for a pitted/burnt centre contact, heat discolouration, and tug-test the terminations.
Clean, bright contacts and terminations that don't move.
Holder looks healthy — check the environment (heat/vibration) next.
Burnt or loose contacts are your fault — replace the lampholder/fitting and re-terminate properly.
View all expected readings at once
Fault-finding flowchart
The same logic as a decision tree.
- 1start
Same fitting keeps blowing lamps
→ step 2 - 2decision
Isolated and dead: is the lampholder burnt, pitted or loose?
Yes→ step 3No→ step 4 - 3result
Replace the holder/fitting and re-terminate — that's the lamp killer.
- 4decision
Heat or vibration problem at the fitting (enclosure, insulation, wattage, shake)?
Yes→ step 5No→ step 6 - 5result
Fix the environment: right lamp, restored clearances, vibration-tolerant lamp.
- 6decision
Is the measured supply voltage sustained near/above the top of the range?
Yes→ step 7No→ step 8 - 7result
Log readings and report the overvoltage to the distributor.
- 8result
Fit a known-quality, correctly rated lamp and monitor — and recheck upstream joints if it recurs.
Common mistakes apprentices make
- Replacing lamp after lamp without ever pulling the fitting down to look at the holder.
- Ignoring the enclosed-fitting and IC ratings on LED lamp packaging — heat is the top LED killer.
- Blaming 'cheap bulbs' when the centre contact is visibly burnt.
- Not measuring voltage at a time the network is lightly loaded, then declaring supply voltage fine.
When to stop & escalate
Evidence of sustained supply overvoltage belongs with the distributor — hand over your logged measurements. Any heat-damaged wiring found at the fitting needs proper repair, not just a new lamp.
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.
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Related faults
Lights flickering
One or more lights flicker — constantly, intermittently, or when other appliances run. Common with LEDs and dimmers, but can also signal a loose connection.
Intermittent dead or flickering load from a loose conductor
Lights or equipment on a circuit drop out, flicker, or come and go — sometimes with tapping, vibration, temperature, or load changes. The classic signature of a loose or partly-broken conductor.
Downlights cutting out then coming back
Downlights switch off after a while then come back once cooled — classic thermal cut-out behaviour, usually from heat build-up around the fitting or driver.