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#139534 11/24/03 02:21 PM
Joined: Sep 2002
Posts: 1,498
Likes: 1
C-H Offline OP
From a Japanese information sheet:

Foreign countries generally employ electric current with higher amperage and voltage than Japan. Plugs and electrical sockets sometimes also differ in physical format. Because all electrical products sold in Japan must conform to requirements of the Electrical Appliance and Material Safety Law, appliances must be modified to work with 100V current and have plugs that fit in standard Japanese wall sockets. Recently 200V current has become available in some parts of Japan, and sales of 200V dish washing machines, electric cookers and heating and cooling equipment have been increasing.

Made me curious: Does it mean that are changing to a 200V only service or simply that they now get two 100V legs = 200V?

Does anyone know anything about the Japanese system? (Apart from the basic 100V, 50/60Hz thing)

#139535 11/24/03 03:58 PM
Joined: Dec 2002
Posts: 1,253
djk Offline
I've visited Japan and superficially at least the electrical outlets look just like NEMA outlets although they seem to have very few grounded outlets and most appliences are Class II with the exception of semi-fixed appliences which had a plug like this:

[Linked Image from] the ground was connected seperately. Adaptors were also available to connect 3 pin plugs up like this..

The voltage is 100 V at 50Hz in Eastern Japan including Tokyo
and 100V 60Hz in Western Japan including Osaka

Apparently power plants in eastern Japan were originally kitted out by European companies and were standardised on 50Hz and Western Japan was electrified by US companies and thus adopted 60Hz .. I get the impression it was something to do with the US occupation of Japan post WWII.

However, Japan seems to have settled on a common 100V system regardless of frequency. I guess it was just too problematic to change frequency.

Almost all modern japanese equipment handles either 50 or 60 Hz but if you are using US equipment it may not be too hapy on 50Hz.

Step up / Step down transformers are available too for sensitive 120V US equipment used in Japan or 100V Japanese equipment used in the USA.

As for 200V supplies I'm sure there must be a higher voltage sytem for use with heavier appliences it wouldn't be all that practical to supply 3KW dishwashers etc on 100V.

I found some stuff on the web saying that you can get 200V single phase at 50/60 Hz or 200V 3-phase supplies in japan for heavy equipment.


What is the official US voltage?

I hear 110V, 115, 120 and even 125V mentioned.

[This message has been edited by djk (edited 11-24-2003).]

[This message has been edited by djk (edited 11-24-2003).]

#139536 11/24/03 04:10 PM
Joined: Dec 2001
Posts: 2,498
Maybe 100/200 3w 1ph AC, but that's just a guess.
Nowadays nominal Voltage in the US is 120/240V. I guess actual voltage can vary from 90 to 130V in real bad cases.

#139537 11/24/03 06:43 PM
Joined: Aug 2002
Posts: 1,691
I wonder why Japan went with such an oddball voltage like 100? Was it to inhibit competition from imported electrical appliances? (Wonder if that's also the same reason for the odd-ball Israeli plugs with the oval pins instead of round.)

Why don't the Japanese power companies crank it up 10 or 20 volts and do the full 110 - 120? Would the existing range of appliances mind it terribly considering they're sometimes built with tolerances up to 127 volts?

Voltage here in the USA ranges from 110 to 120 depending on where you are and what time of day.

My voltage at home in NYC is approximately 117 to 118 volts give or take (readings taken at night).

#139538 11/24/03 07:13 PM
Joined: Dec 2002
Posts: 1,253
djk Offline
100V is a very odd ball voltage alright. I wouldn't at all be supprised if it was choosen specifically to keep US imports out. It's much more fundemental than just using a different connector. Although it's no more weird than the UK's choice of 240V (until recently).

At least with the EU's move to 230V all of the countries in the 220-250V range are being dragged along giving at least one world wide standard system.

I've noticed that in Ireland quite a lot of areas are actually being supplied with voltages closer to 230 than 220 these days. Typically you'll get readings of about 220-225V or even dead on 230.

I remember reading that Perth, Australia was supplied with 250V 50Hz for many years as were parts of India and South Africa.

I presume Australia, South Africa, NZ, South Africa etc are moving to 230V rather than their old 240-250 standards? It would certainly open up a wider range of products.

Is the 120V 60Hz system standardised now?


At least the world, and particularly Europe's, power companies didn't invent as many ways of doing the same thing as the phone companies.

Almost every country in Europe and quite a few others around the world seem to have developed their own telephone connectors. Can be very annoying if you're travelling with a laptop. Thankfully WiFi has arrived!

#139539 11/24/03 09:39 PM
Joined: Apr 2002
Posts: 2,527
The North American Standard is ANSI C84.1-1995. Generally,

120V {and multiples} — “Nominal System Voltage,” and
115V {and multiples} — “Equipment Nameplate Voltage Rating”

The difference allows for circuit voltage drop.

#139540 11/25/03 12:58 PM
Joined: Aug 2001
Posts: 7,520
I seem to recall reading (don't ask me where) that Japanese residential neighborhoods tend to follow U.S. practice in having a large number of small transformers, rather than a big xfmr and an extensive 3-ph 4-w distribution at low voltage as is common in the UK and Europe.

If that's the case, it seems unlikely that they'd have 100/173V 3-phase, so I would assume that they use either simple 2-w 100V or 3-w 100/200V for domestic power.

There is somewhere in the Far East (Korea???) that at one time had a 150V nominal system. Very oddball!

#139541 11/25/03 01:22 PM
Joined: Sep 2002
Posts: 1,498
Likes: 1
C-H Offline OP
I think Paul is right about the 3-wire system. (The 3-phase is also 200V. Delta, I think.)

More curious, I've seen references that the Japanses homes only have a 30A 100V service. In addition, some information sheet made refrences to a "circuit breaker" for the home, as if there was only one. Maybe it's I who misunderstand it or it could be a typo. As I understand it from the few sources I've found the earthing is TT.

#139542 11/25/03 05:54 PM
Joined: Nov 2002
Posts: 794
Likes: 2
100V is a very odd ball voltage alright. I wouldn't at all be supprised if it was choosen specifically to keep US imports out. It's much more fundemental than just using a different connector.

Though American 120V light bulbs would last almost forever on Japanese 100V powerlines. But would look rather brown and be very inefficient.

Other American products of old, like the 5 tube vacuum tube AM radio will work just fine on 100V, if you swap out the 50C5 with a 30A5 or 35C5 audio output tube.

On the other hand, air conditioners will be very unhappy on 100V.

#139543 11/25/03 08:51 PM
Joined: Sep 2003
Posts: 47
I've asked that question somewhere else and was told that Japan had adopted metric at the same time and took 100 as a nominal voltage. Japanese households really didn't get electrified until the 1920s.

Their household plugs at first were lamp-base and then flat blade, same as the US.

I've visited Tokyo a few times. There's a big DIY chain store called "Tokyu Hands", and they have an electrical department.

I remember seeing a 200V plug. It's like a NEMA 2-15P, no ground pin. So just like the US, I guess they add the two service 100V hot wires to get the 200V.

Btw, here's a ref chart for NEMA plugs:

I brought back a few Japanese household receptacles from Tokyu Hands. The faceplate just snaps on and the connections are push-in. Of course it's ungrounded NEMA 1-15R, white lead neutral. The rating is 125V 15A.

The only place I saw a grounded receptacle was at a donut shop, probably where 100V voltage grounded appliances are used.

I also bought a voltmeter and measured the line voltage and it was 105.

Also, there's a place in San Francisco's Japantown that sells some 100V appliances and stepdown wall transformers to bring 120 to 100V.


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