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I have been wondering why 120V and 230V countries have different threads. Is the reason just historical inertia or design based due to different voltages? I found out that the E26 and E27 threads for full sized bulbs seem to be designed for different voltages, the E27 having a larger insulator to cope with 230V.

What about the smaller threads such as the E12 and E17? I have not been able to find anything on these threads. I have lots of E17 lamps at home (Christmas lighting I run on a stepdown transformer.) When when I compare those to a typical E14 socket I can't see a difference in the size of the insulator so I believe technically they should be as good as an E14 socket, they are infact beefier.

I've also found E12 lamps being sold for 230V (Amazon/aliexpress) so I believe those are definitely OK for 230V unless there's something shady going on.

This is idle curiosity on my part, arising from having and handling a lot of American 120V Christmas lighting (I like it) and running it all on step down transformers. I don't really have any plans to try and run it on 230V, it's safer to run this stuff on 120V.

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I have been wondering why 120V and 230V countries have different threads. Is the reason just historical inertia or design based due to different voltages.

A 120 V incandescent lamp will burn out immediately if fed with 240 V so using different thread sizes to prevent this would be a useful contribution to safety. Some of the Edison thread sizes aren't sufficiently different to do this effectively.

Wikipedia has a large amount of information on its Edison screw page.

For safety and long life modern Christmas lights have migrated to LEDs running at ELV (Extra Low Voltage).

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  • \$\begingroup\$ This has nothing to do with the question \$\endgroup\$
    – Dennis
    Commented Dec 7, 2023 at 8:09
  • \$\begingroup\$ @Dennis Which question? You've asked about the history of the design and also about safety. What's your definition of safe? Meets international standards? Now or at the time of introduction of each thread design? National standards? Which country you in? Safe for small children to clamber over your Christmas tree? If you're looking for someone to sign off on your collection of the imported Christmas tree lights no one's going to do that without physical inspection and test. If you ask a vague question you can expect a vague answer (or none). \$\endgroup\$
    – Graham Nye
    Commented Dec 7, 2023 at 14:20
  • \$\begingroup\$ Are E12 and E17 threads 230V safe? Not needing anyone to sign off on anything since I won't be running 230V through them and have no plans to. \$\endgroup\$
    – Dennis
    Commented Dec 8, 2023 at 10:40

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