Japan is the only country with a developed economy split into two incompatible power grids. Tokyo and everything east of the Fuji river runs at 50 Hz; Nagoya, Osaka, Kyoto and everything west runs at 60 Hz. The two meet at a handful of frequency converter stations that can move only about 1 GW between them — roughly 1% of peak demand.
How it happened
In 1895 Tokyo Electric Light bought German AEG generators, which ran at 50 Hz. A year later Osaka Electric Lamp bought American General Electric generators at 60 Hz. Both companies expanded into their own regions, and by the time anyone thought about compatibility, the country was wired twice.
Does it matter for travellers?
Rarely. Japan is also unusual in running at just 100 V, and its sockets are the ungrounded Type A two-pin (with Type B in some newer buildings). If you arrive from North America, your plugs physically fit and the voltage is close enough for dual-voltage electronics.
Frequency only bites in three places:
- Clocks that count mains cycles will gain or lose 20% of their time across the boundary.
- Motors — older fans, record players and some hair dryers run 20% faster on 60 Hz than the 50 Hz they were designed for.
- Anything with a transformer designed for one frequency can run warmer on the other, though modern switch-mode supplies do not care.
What to pack for Japan
- A Type A adapter if you are coming from Europe, the UK, Australia or India — Japanese sockets take the flat two-pin only.
- Nothing at all if you are coming from the US or Canada, unless your device has a Type B plug with an earth pin: many Japanese sockets have no earth hole.
- Check your charger says 100–240 V. Most do; a 120 V-only device will underperform at 100 V.
Where the boundary is
The dividing line runs roughly through Shizuoka prefecture, north through Nagano and Niigata. Hotels on either side will have the local frequency, but a modern laptop or phone charger will not notice which half of the country it is in.