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I recently tried to change a bulb using an adaptor (converting from a E27 to B22 fitting). After switching on the light fitting the fuse had blown. After inspection it turns out the adapter is faulty and must have caused a short-circuit.

After removing the bulb and resetting the switch in the main fuse box, I am now unable to operate the switch on the wall to turn the fitting off (the switch physically won't click).

Is there something I can do to fix the problem?

Thanks,

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  • Any further information on this? If you replaced the switch, it would be great for you to take it apart and let us know what actually happened to it (a picture would be awesome).
    – Daniel Griscom
    Commented Jan 3, 2017 at 15:44

1 Answer 1

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What happened is that when you turned the switch on, the shorted adaptor drew an enormous surge of current through the switch. The fuse almost immediately blew and prevented a fire, but not before the switch contacts were welded together, forever locking the switch on.

The fact that the switch no longer "click"s is another symptom of the problem. The switch lever may still move, because they're generally connected to the contacts through a spring; this is to give them a "snap" action, but also allows the lever to move when the contacts won't.

You'll at least have to replace the switch; you may want to get an electrician to look over the entire circuit for damage.

Edit: here's some more info. First, an "autopsy" of a toggle switch whose contacts welded: https://www.youtube.com/watch?v=B306JLFjpqs

Second, a switch manufacturer's FAQ on the causes of contact welding: http://www.omron.com.au/service_support/FAQ/FAQ02182/index.asp

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    That is dangerously awesome.
    – Dan Z
    Commented Dec 30, 2016 at 22:08
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    This is exactly what I had in mind. The "enormous surge" probably damaged something else. It's a good idea to check if the cabling is all intact as well.
    – Ismael Miguel
    Commented Dec 30, 2016 at 22:24
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    What @IsmaelMiguel said. If the switch is broken, there's a good chance that something else is broken as well. I very strongly recommend OP to contact an electrician and have them go over that circuit before reapplying power.
    – user
    Commented Dec 30, 2016 at 22:30
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    @IsmaelMiguel That said, imagine if there hadn't been a switch; the wiring should be able to withstand a short until the fuse blew. Adding the switch could only lessen the damage to the rest of the circuit. So, I don't see damage to the rest of the circuit as being of great concern.
    – Daniel Griscom
    Commented Dec 31, 2016 at 14:42
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    Being a professional electrician I rarely find damaged conductors unless back stabs were used and the breaker oversized to 20 amp. 14 awg wire can be protected at 100 amps inside a motor control enclosure the fact that it blew immediately I would check in the box if no damage there the wiring is usually ok since the light is on any splices are working.. Note an inverse time breaker even a 20 amp will trip between 60& 100 amps in approx .01 seconds based on the trip curves so there is not enough time to overheat the insulation.+
    – Ed Beal
    Commented Nov 1, 2018 at 22:22

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