Bayonet lightbulb bases

[D.M. Procida]

Is it possible for the metal base of a normal bayonet lightbulb to become live, under normal circumstances?

Daniele

[Dave Plowman (News)]

No earth to the metal bit in a plastic bulb holder. And it is possible to touch it if you try hard enough.

[Mr Pounder]

What metal bit in a plastic bulb holder?

[The Natural Philosopher]

Not under normal circs, but its a common fault

[DavidM]

Many plastic bulb holders have a metal insert in the outer case - the part that the bulb "lugs" twist in to. Plastic only ones seem to break off quite easily after they become brittle.

I wasn't sure when the OP said lightbulb bases whether he meant the buld hodler or the base (neck) of the bulb itself.

[Graham.]

He?

[Graham.]

Yes, sometimes the connecting wires are not trimmed properly and protrude from the solder blobs.

[D.M. Procida]

I meant the part that forms the mechanical locking system that is part of the bulb itself (usually it's metal, on some it's plastic). I didn't mean the holder in the light fitting.

Daniele

[Bob Minchin]

Yes! He

We had this a while back

[John]

Yes but only if there is a fault or defect. They should be earthed which would prevent it becoming live if there was a fault.

If they get *very* hot, like in an antique photographic enlarger, the black stuff might become conductive (probably just before it melts).

rusty

[Nick Leverton]

Even the cheapest fittings I've come across use thermo-setting plastics, which don't soften in the heat. Before about 1950 the only plastic available was Bakelite, which is thermo-setting. Though they can go brittle if continuously over-run. And yes I did have a Russian Zenit enlarger !

Nick

[Ron Lowe]

Possibly, under unusual circumstances.

An example I can think of might be: if the lamp were installed pointing upward, and the fillament failed, might it be possible that the dangling end would contact the metal base?

But the metal base would be almost 100% encased in the lampholder, and un-touchable by fingers.

It's not something I've spent a lot of time worrying about.

Worse would be a light fitting with no lamp in it, exposing the live prongs. Handy for having at intruders, I guess.

[D.M. Procida]

By fingers, yes.

I bought a couple of Habitat Garland metal light shades.

Though they come with a ring to prevent tendrils of the shade making their way towards the base of the bulb (you'll have to look up the shade if you re not familiar with the one I mean) I can see they could make contact.

Daniele

[chris French]

as has been said, in normal circumstances, the metal base of the bulb shouldn't become live anyway.

I take it this is a shade, not a complete fitting (metals fittings should be designed to be earthed) If you are worried about it then I would make sure that the fitting is an earthed fitting (a standard plastic pendant fitting isn't, so you might need to change it)

Note, most systems will have an earth cable in the lighting circuit, but older (back to the '60's sometime?) might not, or it might have been cut back and the fittings/switches and not connected

[John]

This was a "Gnome" enlarger older than the cold war, bought second hand. It all became live due to the 150w bulb getting too hot and leaking current to the unearthed metal bayonet socket. Fortunately, wearing rubber soled shoes, I lived on to see the digital camera era which is a lot safer.

I recently had "bakelite" MES sockets with 60w tungsten bulbs in a cooker hood go up in smoke and flames due them carbonizing and shorting out. Good reason for using MFLs

rusty.

[Dave Plowman (News)]

Or buy a decent quality cooker hood with ceramic/brass bulb holders. For the heat. And CFLs don't like heat.

[Andrew Gabriel]

[wrote this a while ago, and forget to post it]

No, not under normal circumstances.

I know of two ways it has happened...

One of the supermarkets (which I won't name, because I might not have correctly remembered which it was) got a batch of faulty bulbs where some of the wires to the base contacts were not trimmed off, and poked out of the solder. These could bend around and make contact with the side. They were prosecuted. This was probably about 25 years ago, and it's the only case of this I know of.

Some patress mounting lampholders have 3 contacts. The third one is sometimes an earth connected to metalic sleeve in the plastic molding, or is sometimes an isolated loop-in terminal. If it's an earth and you use it as a loop-in terminal, then you have a live sleeve.

AFAIK, there are no recorded fatalities resulting from bayonet cap lampholders, either as a result of this, or due to people sticking fingers into an empty lampholder (probably can't get a large enough contact area to pass enough current, and there's no chance of the "can't let go" syndrome). OTOH, there are many recorded cases of fatalities involving ES lampholders, normally due to the side contact being live, and the way you might grip the lamp base to unscrew it.

[Graham.]

I stand corrected!

[Graham.]

all became live due to the 150w bulb getting too hot

wearing rubber soled shoes, I lived on to see the digital

go up in smoke and flames due them carbonizing and

My Beta II wasn't as old as that. It's still languishing in the garage, here it is.

I know what you're all thinking, you can't get proper insulating tape these days. Of course the 13A plug came later, originally it was a bayonet adapter.

[Graham.]

I was going to post that there was more chance of the yanks adopting decimal currency than our bayonet cap lightbulbs.

Posting it anyway for your amusement.

I wonder if anyone has patented some sort of super safe shuttered lampholder?