Arcing, bulbs blown, melted metal: what's the deal?

Forums › Home Workshop DIY › Arcing, bulbs blown, melted metal: what's the deal?

pih

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#295418 27-Mar-2022 21:33

A week and a half ago I went to turn on the rangehood light and got a huge fright when I heard and saw heavy arcing, blue light instead of the usual white, followed by a pop and the circuit breaker cutting out.

After cautiously checking everything over and not seeing anything unusual - just one slightly blackened bulb, I turned it all back on and it was all working again, sans said blackened bulb. "Oh," thought I, "must have just been a very loudly blowing bulb". Shrugged and didn't think much more of it. One bulb was still working.

I've just turned it on again and - BZZZ.... POP - same thing again. This time I removed both bulbs and found something I can't explain easily: they are E14 (Small Edison Screw) and the screw thread on both has been completely vaporised in parts:

Any ideas what could have caused both bulbs to fail so spectacularly, so close together? Clearly there's an internal short there: bad batch? Poor construction? Oil or moisture ingress? I've seen a lot of blown bulbs and never seen anything like this before.

elpenguino

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#2892924 27-Mar-2022 21:42

No, ironically an open circuit could be more risky in this case than a short.

An open could lead to arcing which raises the temperature greatly.

Ensure the new bulbs are screwed all the way down. Check the socket for debris, grease etc. Clean if necessary, safely of course.

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Gordy7

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#2892925 27-Mar-2022 21:42

The top bulb does show some corrosion around the tip.

What are the sockets like?

Can you see anything unusual behind the sockets?

How old is the rangehood?

Gordy

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pih

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#2892926 27-Mar-2022 22:03

Gordy7:
The top bulb does show some corrosion around the tip.

What are the sockets like?

Can you see anything unusual behind the sockets?

How old is the rangehood?

Sockets are in pretty good shape. One has no corrosion or charring on the contacts, the other only has a little, and not on the contact point. Nothing else unusual. Rangehood is probably only 3-5 years old, we've been here for 1.5 years and never had a problem with it.

pih

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#2892929 27-Mar-2022 22:18

elpenguino:
No, ironically an open circuit could be more risky in this case than a short.

An open could lead to arcing which raises the temperature greatly.

Ensure the new bulbs are screwed all the way down. Check the socket for debris, grease etc. Clean if necessary, safely of course.

Interesting, I hadn't thought of that. You're probably right that the bulb filament blew when switched on (open circuit) then the internal wires from the screw to the bulb stem were too close and arced as soon as it became the path of least resistance - so probably a manufacturing fault as well I suppose. I did notice that both bulbs had indeed blown as well.

Certainly makes sense, thanks!