Japanese JIS 8303 – Japan

The standard to which Japanese plugs are manufactured is JIS C 8303, and the cable is C3306. C3306 includes three cable types: VCTF, a 3-core round flex for normal use; HVCTF for high-temperature use; and VCTF-K is a 2-core oval cable. The cable’s core colours are black, white and green. IEC connectors are covered by Japanese Standards Association J60 320.

Approval is by PSE and/or JET: all Morvan Japanese PSE JET cable and PSE JET plugs carry the appropriate approval. These include Longwell LP-53 for the 3 pin, and LP-51A for 2 pin.

For larger appliances we can also supply 100V 20A and 200V 15A plugs and sockets (in residential settings usually air conditioning). We also offer 200V 20A rewireable plugs for e.g. heaters.

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Mains frequency in Japan – 50 or 60 Hz?

Japanese mains voltage is 100V AC, but at two discrete frequencies: northeastern Japan on the Tokyo grid (including Yokohama, Tohoku, Hokkaido) uses 50 Hertz (Hz), while southwestern Japan on the Osaka grid (including Nagoya, Kyoto, Hiroshima, Shikoku, Kyushu) uses 60 Hz.

Normal appliances should not be affected, but electrical motors, clocks and timers may run faster or slower; more modern equipment is now designed to run on either frequency.

Why is this?

In the early days of electricity, a German 50-hertz generator was imported by the Tokyo Electric Light Co in 1895, while a year later and 500km away Osaka Electric Lamp brought in a 60 cycles generator from the USA; slowly the rest of the country was wired on to one of the two circuits until it was too late and too expensive to standardise.

This is a barrier to deregulation of the energy market as it creates a quasi-monopoly in some areas. It is also especially problematic in disaster scenarios when power cannot be simply routed from one area to another if the frequencies do not match.

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JIS8303

Japan originally used North American type 15A plugs, but has since developed its own standard. The main differences are that manufacturing tolerances for the plug are stricter, and metric mm2 VCTF cable is used. Plugs and cables must also be Japanese-approved. A 5-20 20A plug similar to the American one is also used, along with 250V 6-15 and 6-20.

Pre-2005, older Japanese power outlets had no requirement for a third receptacle to accept a plug with an earth pin; earthing is via a special earth post or the screw that holds the faceplate. For this reason, there exist special Japanese 2-pin plugs with a flying earth lead, that can be connected to the earth screw with a crocodile clip or screw-down terminal. Morvan can also supply adaptor plugs. From 2022, the requirements for grounded sockets were further formalised in updates to 3202-3 Internal Wiring Regulations.

Older sockets are unpolarised, i.e. have the same size apertures. The 1961 Electrical Appliance and Material Control Law (‘Dentoriho’) mandated the larger 9mm aperture as neutral and smaller 7mm one as line. This was to prevent equipment damage from reversed polarity, but with modern equipment it is no longer a real issue as the only change is the inversion of electrical phase. Sensitive appliances, e.g. audio uses, will have a polarised plug which prevents this. Neutral is labelled ‘W’ similar to North America.

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The quality of electrical appliances and their corsets in Japan is overseen by the PSE DENAN law from the Japanese Ministry of Economy, Trade and Industry (METI), formerly known as DENTORI. The DENAN symbol, PSE diamond (specific), PSE circle (non-specific), ‘<PS>E’, or JIS approval is required on electrical products in Japan. All Morvan Trading’s Japanese power cables are independently tested by the Japan Electrical Safety & Environment Technology Laboratories ‘JET’ test house, and our approved products either carry PSE or PSE JET markings.

A Japanese medical or hospital-grade plug is specified in JIS T 1021 and JIS C 3005, which we offer in grey, but these are not mandatory requirements in hospitals.

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