Why don't american lightbulbs fit into european sockets?

[Lampje]

Hi there,

I am new at this forum.
I am living in the Netherlands and have the next question: Why don't american lightbulbs fit into european sockets?
I collect lightbulbs for a long time now and discover that the american lightbulbs (E27 base) don't fit in our sockets (most of them)
The opposite fits.
Is there anybody who has the same experience?
Or is there someone who can tell me the difference between the american and the european E27 base?
I am very curious about your answers.


Best regards,

Wieger Nieuwenhout
Leeuwarden, The Netherlands

[Chris W. Millinship]

The American "Standard" screw base is actually E26, and that millimetre can make quite a difference since the thread depth and pitch are slightly different too. It depends on the type of socket and the tolerances it (and the lamp bases) are made to, some will fit either type and some won`t from what I`ve found.

[Lampje]

Chris,

Thanks for your reply.

I found out that european lightbulbs will fit into an american socket.
So these sockets must be wider as the european sockets.
But if an american base measures 26mm how would this work out?

[Chris W. Millinship]

It`s probably to do with the thread depth. American E26 lamp bases appear to have shallower threads than European E27. The diameter is the overall measurement at the widest point but if you measured the diameter at the narrowest, in other words at the depth of the threads, an E26 base would probably be slightly wider than an E27. As a result, the narrowest part of European lamp sockets will often end up being a bit too narrow to fit a US lamp base, even if the widest part is large enough to fit. The thread pitch is slightly different too which adds to the problem. I do have some US sockets that won`t properly fit European lamps, and vice versa, it`s probably down to manufacturing tolerances in the end.

[Lampje]

Chris,

Thanks you very much for your explanation.
It will be the best to get american sockets for american lamps.
Just one thing.
I have a few Dim a Lite's and they fits into all european sockets I have, so for export they use the european standard I suppose.

[Anders Hoveland]

Perhaps because it is potentially dangerous to put an American bulb into a socket in Europe. Double the rated voltage means quadruple the wattage, for any given resistance.

[Lampje]

Hello,

I never thought of that possibility. That would be a good reason.
Our voltage is 220/230 Volts, almost double of yours.
But not all the light bulbs from your continent has this problem I discover.
Some do fit excellent. Maybe they were intent for export?

[Howard]

Perhaps because it is potentially dangerous to put an American bulb into a socket in Europe. Double the rated voltage means quadruple the wattage, for any given resistance.

Highly unlikely.  The reason is more likely to be historical.
Early manufacturers in Europe and USA adopting slightly different standards when they did standardise their products.
Besides, ES (E27) capped lamps have been available in Europe since the early days of capped lamps, in a wide range of voltages from a few volts to 260 volts, depending on intended use, all with the same cap dimensions.

[Howard]

Maybe they were intent for export?

Unlikely, unless marked for that purpose.  Unfortunately, such marking was/is probably only on the export manifest!
More likely historical differences between the standards used by European manufacturers (E27) and those in USA (E26).
See also my reply to Anders Hoveland, and earlier posts from Chris Millinship.