The Lemon Fool

About 2 months ago I bought a 7watt bayonet LED bulb for a table lamp. But yesterday the bulb failed blowing a 3A fuse and tripping a RCD.
DAK why this should occur and if it is normal when a LED bulb fails?

Not in my experience. But I've had lamps that have tripped the RCDs when the lampholder itself fails. And I've got a bayonet LED bulb right here that's got to go back to the shop because the two soldered 'tails' that carry the contacts aren't big enough to make clean contact with any of our light fittings. I could well imagine that such a bulb could get hot if it was only contacting intermittently.

BJ

Mains LED bulbs have some circuitry built in to reduce the voltage down to the level required by the LEDs. It is that circuitry which is directly connected to the mains. So it could fail short circuit and blow fuses or circuit breakers. I've never known it happen. But I'd say, possible. That's why we have fuses and circuit breakers

Gryff

In theory, a short (unless it is to earth) shouldn't trip an rcd. Is it a brass lampholder? You should be able to run 100 of these through a 3A fuse without it blowing.

Julian F. G. W.

ivahunch wrote:. DAK why this should occur and if it is normal when a LED bulb fails?

As Julian has said, the RCD would normally only trip if the fault was between a live conductor and Earth. A 3A fuse would normally only blow if either a large current, much greater than 3A, were to suddenly flow or a current a little bit higher than 3A were to flow for a prolonged period.

Normally when an LED lamp fails (not that they do much) they just cease to light with no circuit breaker tripping.

So it almost sounds to me like your light fitting has a fault to Earth. Has it been subjected to any abnormal mechanical, er, stress?

Have you tried the LED lamp in another fitting to verify it is truly defect?

Cheers
Chris

Have you tried the LED lamp in another fitting to verify it is truly defect?

Yes and I also used a circuit tester to confirm the LED has failed. The table lamp works fine with another bulb. So I don't think the lamp is faulty.

ivahunch wrote:Yes and I also used a circuit tester to confirm the LED has failed. The table lamp works fine with another bulb. So I don't think the lamp is faulty.

In that case it does indeed sound like the LED lamp developed a fault within it as Gryff surmised. If the LED lamp has a metal part that touches a metal bayonet lampholder then I suppose the fault could have been to Earth (normally a requirement for an RCD to trip). There is another scenario though that can cause RCDs to trip without an Earth fault. It can also happen if the risetime of its load current is very short. So perhaps that is what happened in your case.

Incidentally lightning strikes (or even sudden voltage spikes from heavy duty equipment) on the input of an RCD can cause them to trip.

Regards,
Chris