Melted

[Nancy]

If you don't need "nancy boy" circuit breakers why do all your plugs have "nancy boy" fuses?

[Tim Streater]

You're not seeking to do that deliberately, but it may happen - especially if the bulb is hard to get out due to having been screwed in too tight.

[charles]

whereas bayonet bulbs never jam in their sockets?

[michael adams]

Screw in light bulbs were developed by Thomas Edison.

It would be interesting to know the precise details of the thousands of experiments he must have conducted at Menlow Park which led him to conclude that screw fittings are in any way superior to bayonets.

michael adams

...

[michael adams]

How would that happen ? The bulb is secured in the slot by the spring in the socket. For the bulb to jam presumably the spring would need to jam or break in the open position. Which would be malfunction in the apparatus and totally divorced from possible human error.

On the other hand one of the supposed benefits of screw fit bulbs is that when fully screwed home they are more secure than a bayonet fit bulb.

However among possible disadvantages -

"It is possible to over-tighten the screw and jam the bulb"

This is a fault which is solely the result of possible human error.

Basically screwing and unscrewing threaded bulbs requires a degree of judgement and finesse which isn't required when using bayonet bulbs. And can't necessarily be taken for granted, But then Thomas Edison was not only an American but was a genius, right ?

michael adams

....

[NY]

Yes, I'd love to know what made him go for a screw thread. It has so many disadvantages:

a) outer screw is connected to one or other of the wires, so there is a

50:50 chance that it will be live when you are changing a bulb

b) it takes longer to unscrew a bulb, involving several 360-degree turns, than to remove a bayonet that requires maybe a 10 degree turn

c) because there is a lot of surface area contact between bulb screw and fitting screw, there is much greater friction and much greater chance that corrosion or a slightly oval fitting/bulb will cause the bulb to bind in the socket

The third is the biggest problem. I've found that a bulb which has been in its socket for several years has stuck to the fitting, even with bayonet, and the glass has become loose from the metal. The usual mode of failure in those cases is that you press and twist, and the glass comes away, leaving the metal cap in the holder. If that is possible even with a bayonet, think how much more likely is is to happen with a screw fitting.

And yet not only the US but also a lot of mainland Europe uses these stupid fittings. I'd always thought that it was a 120V versus 240V thing (to prevent a 120V bulb being used accidentally on 240V), until I saw that all the light bulbs that are sold in Ikea have screw fittings, so evidently those are used in Sweden.

[charles]

I've had springs jam and the result can be that the bayonet holder becomes detatched from the bakelite of the rest of the fitting.

[NY]

It is the springs in the two pins, pushing the lugs on the side of the bulb cap against the lip in the wall of the fitting, which holds the bulb in place. If the springs failed, there would be no pressure and the bulb would be more likely to come out if the whole lamp was jogged. The two things which cause bayonet bulbs to seize in the fitting are:

a) spring-loaded pins corrode and can no longer be pushed inwards as the bulb is pressed in to turn and remove it

b) thin metal in fitting gets distorted (eg due to fracture of the heat-resistant plastic surrounding it) and/or metal surround or cap get corroded

The first can happen if there is water damage (eg condensation in a bathroom while the light is turned off) over a long period of time. The second can happen if the fitting gets very hot (poor ventilation) and/or the fitting is poor quality.

[Tim Streater]

Not seen it happen, whereas I had trouble in the US with some screw-in bulbs.

And in any case, with a bayonet, one would be less worried as no part of the base is live, even if the wiring was done wrong.

[Rod Speed]

There weren't thousands of experiments on that. He just made a choice, just like any other designer always does.

[Rod Speed]

Corrosion between the bulb base and the socket.

Yes.

That?s just one way.

Same with corrosion.

Nothing supposed about it, they are.

Never had that happen, essentially because the central contact deforms if you do over tighten it.

In practice it doesn?t.

And produced a much better arrangement whose main downside is that is possible to wire the socket so the outer is active.

[Rod Speed]

But you do that so rarely that its no big deal and its much more secure in an ES socket.

Never had that happen, even with external bulbs.

Nope.

Never had that happen with ES bulbs and almost all of mine are.

Never had that happen with ES bulbs and almost all of mine are.

Nothing stupid about them.

In fact they are much more common world wide than bayonet.

[James Wilkinson Sword]

Not so much of a problem now we don't use baking hot incandescents.

[James Wilkinson Sword]

Bullshit. When you wire the light socket, you connect live to the centre pin. Only ones wired very badly will have live on the outside.

But I need two hands to undo a bayonet, as a fair amount of force is required, so I have to hold the fitting steady with my other hand. If I'm balanced on a stool or ladder, I'd rather not use two hands.

And presumably for the same reason, better electrical contact.

I've seen that with 100W incandescents in places where they last for years, like a garage or attic. But now they're all LEDs, it doesn't happen, and they're not glass anyway.

[James Wilkinson Sword]

Protection against fire, not electric shock. I'd prefer my house didn't catch fire while I was out and therefore not able to put the fire out before I lose valuable property or pets.

[Diesel]

If the socket is properly wired, touching the easiest piece of metal you can accidently stick a finger onto shouldn't do anything to you. It *should* be the neutral side. The hot side is supposed to be the pin, in the center, in the bottom. If you manage to touch that, you should ask someone with more intelligence to change lightbulbs in the future for you. If the socket is improperly wired, it should be corrected so that you don't accidently shock yourself again in the future.

[Diesel]

If the socket is properly wired, that part of the socket should be on the neutral side. NOT the hot side. That being said, touching it shouldn't be a shocking issue for you or anyone else.

[Diesel]

As is getting shocked if you make contact with the screw lining. It should be on the neutral line, not the hot line. If it's hot, your socket isn't wired properly, due to human error.

[Diesel]

Not if it's properly connected. The hot should be connected to the pin and only the pin.

I've never had it happen to me, but, I've succesfully removed damaged bulbs from other peoples fixtures with nothing more than the power off and a potato chopped in half. It's not rocket science. And, if the socket is properly wired, the screw side isn't hot in the first place...

[Diesel]

I've got a few modern 'old' looking LED lights that are glass. They even have the oldschool filaments (it's LED) to give it the old timey look. Even supports dimming. If you're into that sort of thing. And if you're using a bulb rated for a higher wattage than the socket (and in many cases people did/some do), excessive heat build up is the result of user error.