Japan's invisible electric wall

Looking for vintage clocks

Japan’s mains electricity comes in two different frequencies with half of the country using 50 Hz and the other 60 Hz.

I stumbled onto this while shopping for vintage desk clocks on eBay. I already knew about the voltage difference — Japan runs on 100 V, the US on 120 V, same-looking plugs notwithstanding. Back when I tried to buy a Muji toaster oven, I stumbled upon reviews of the brave souls who learned the hard way why you shouldn’t import one. They talked about how the low setting was pretty much high, and the highest setting would immediately burn its contents.

This isn’t a problem with most low-power electronics, since they use USB-C or a power brick that supports a wide range of frequencies and voltages and converts it to the right DC voltage. So while I was looking for clocks, I found plenty that would work in the US, like this Copal 222 that can do anywhere from 80 to 120 V at 60 Hz.

But then I noticed something weird. First up is this Seiko flip clock shaped like a wooden ball. On the back it says it takes 100 V at 50 Hz, with a warning to check the mains frequency when using it.

Then I find another Seiko flip clock with a switch on the back between 50 Hz and 60 Hz. Is that switch for using in a different country?

I remember in older PC power supplies there was often a switch between 120 V and 240 V, but I don’t remember seeing a switch for the frequency.

The electric wall

I looked at the table of mains voltages, frequencies, and plugs on Wikipedia and discovered that not only is Japan the only country that uses 100 V, but that its supply frequency is both 50 Hz and 60 Hz.

I became more curious when I looked at a map of Japan and noticed that the western half uses 60 Hz while the eastern half is on 50 Hz, with a border in the middle where some places seem to use both.

Marveling at railfans’ maps

Coincidentally, I bumped into the invisible wall again when I was browsing OpenRailwayMap, a collaborative project based on OpenStreetMap technology aimed at mapping railroad lines worldwide. Looking around Japan, I noticed a couple of things.

If you follow the Tōkaidō Shinkansen (bullet train) from Tokyo towards Osaka, you’ll notice all the conventional rail lines that generally use DC power. But you’ll also see the New Transit Yurikamome running nearby — and that one runs on 50 Hz, while the Tōkaidō Shinkansen runs on 60 Hz. 50 Hz is expected, since that’s the mains frequency in Tokyo.

Tōkaidō Shinkansen in red and New Transit Yurikamome in light green

You see, when the first Shinkansen was constructed, given that most of the route was in the 60 Hz section of the country, the portions that fell in the 50 Hz section had frequency conversion substations installed to standardize the entire line at 60 Hz.^[1] They’ve continued to upgrade these converters for efficiency and reliability till today.

Tōkaidō Shinkansen route in red

But the 50 Hz/60 Hz divide doesn’t stop with the Tōkaidō Shinkansen. It gets more interesting with the Hokuriku Shinkansen, which we recently took from Tokyo to Kanazawa. When that line opened in 1997, it was known as the Nagano Shinkansen — helpful since it terminated in Nagano and would take tourists to the Nagano Olympics. It was the first Shinkansen to have trains (the E2 series) capable of operating on both 50 Hz and 60 Hz overhead lines because reaching Nagano required crossing that boundary. E4 double-deckers were later added to the line, also equipped for both frequencies.

E4, left and E2, right (ykanazawa1999 on Flickr)

When the extension to Kanazawa was completed in 2014, the line was renamed to its original intended name: the Hokuriku Shinkansen. The full route crossed the frequency border three times, meaning the new E7/W7 trains also carry dual-frequency equipment like the E2 and E4 before them.

Hokuriku Shinkansen route in red

How did Japan get here?

So there’s this wall down the middle of Japan, but how did it get there?

The first large electric generators in Japan were purchased by the Tokyo Electric Light Company around 1895–96 and supplied by AEG.^[2] A year or two later, they bought more from Siemens. All of these German generators operated on three-phase AC at 50 Hz. But a competing company, the Osaka Electric Light Company, purchased generators from General Electric, which operated at 60 Hz. Though the system was small at the time, there was already fragmentation between Japan’s two largest cities.

Vintage postcard of a substation (Edo Tokyo Museum)

Over the following decades, more electric companies sprung up and purchased their own generators. In 1939, during World War II, the Japanese government established the Japan Electric Generation and Transmission Company to control electricity generation and transmission — mainly to eliminate overlapping facilities and competition. They consolidated the commercial frequency: 50 Hz in the east, 60 Hz in the west. There were talks of unifying on a single frequency, and those talks have continued ever since.^[3] But there was never enough political will to bear the cost of replacing one set of machinery with another.

By 1965 — just after the introduction of the first Shinkansen — the Sakuma Frequency Converter Station was completed,^[4] allowing 300 megawatts to be exchanged between the eastern and western grids. It wasn’t much, but it connected Japan’s two sides.

Ribbon cutting for the first Shinkansen in 1964 (Asahi Shimbun)

As Japan’s electronics industry grew, products like the clocks I was looking at came with warnings about where in Japan they could be used. Moving across the country could mean having to replace electronics entirely. This was especially critical for vinyl turntables, wall clocks, and anything else that relied on mains power for timing. Bring a turntable from one side of the country to the other and your music would play just a little too fast or too slow.

Blackouts in the 21st century

The effects of this split go beyond inconvenience. Japan has built more frequency converters and expanded their capacity, but can still only transmit a bit more than 1 gigawatt across the boundary (less than 1% of Japan’s power capacity).

That was a real problem in 2011 after the Tōhoku earthquake and tsunami, when Japan had 142 gigawatts of power capacity — 27 of which were taken out of service following the earthquake and the disaster at the Fukushima nuclear facility.

The result was rolling blackouts in Tokyo and surrounding areas, even though western Japan had spare capacity it could have sent over.

Voluntary blackout in 2022 after an eartquake (Bloomberg)

After Fukushima, Japan shut down its nuclear reactors and started relying on liquefied natural gas. It has since begun starting nuclear plants back up. Part of this is a response to Russia’s 2022 invasion of Ukraine, which reminded Japan how vulnerable it is to fossil fuel prices. Part of it is the AI boom and the related surge in data centers and semiconductor factories, which have increased domestic demand for power. An anti-nuclear movement remains vocal, but Japan’s new Prime Minister, Sanae Takaichi, is a proponent of nuclear energy, with Japanese companies developing new reactor designs.

In recent years, nearly every existing frequency converter has begun an upgrade, with plans to add another 1.5 gigawatts of cross-boundary capacity — small, but a meaningful buffer in a future incident.

Legacy of early decisions

It’s easy to imagine Japan as a monolith, composed of clean, standardized systems. But Japan’s electrical grid still bears the scars of 19th-century competition. The country’s trains cross invisible electrical borders, enabled by frequency converters humming in substations.

Next time you come across vintage Japanese electronics, flip them around to see how they handle different mains frequencies. You might find a tag with a small map of where that product could be used. Or next time you’re riding the Shinkansen, think about those invisible borders it crosses.

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1. 50 Years of Tokaido Shinkansen History · Japan Railway & Transport Review ↩︎
2. 50-Hz frequency: how the standard emerged from a European jumble · IEEE ↩︎
3. History of CIGRE · The Japanese National Committee of CIGRE ↩︎
4. Sakuma Frequency Converter Station, 1965 · IEEE ↩︎

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Thanks to Q for reading drafts of this.