is third transformer hole an earth?

No. If the power 'brick' has three pins, it has been designed to require three connectors.

"Only" an earth? Sheesh!

Assuming that your existing power brick can accomodate Japanese mains voltage and frequency, you will need an earthed Japanese plug to fit the Japanese mains socket. Which sounds like what the technical services department are trying to convince you of.

I think Japan uses 100V mains at either 50 or 60 Hz depending on location.

If the "power brick" is a switch-mode converter (not an iron cored transformer) some types automatically adjust to anywhere between 100 - 240V, check the specification label as this information should be clearly marked.

Most PSUs of this type are double insulated and do not require an earth, they only have a 3-pin plug because the regulations in the country of use say that all wall sockets must be 3-pin (there wouldn't be much point in supplying items with a 2-pin plug that didn't fit anything). Carefully examine the mains lead, if its round then it contains 3 wires and must be earthed, if the mains lead is flat so you can tell the outer covering is over a pair of wires side by side then there is obviously no third wire for an earth.

True enough.

I took the OP to mean that the brick itself has three pins in the orifice to which the incoming mains lead is connected. That suggests that the makers of it expected it to be earthed.

Both the laptop power bricks in use in this room (one HP, one Toshiba) have three metal pins for the mains lead to connect to - and /do/ require an earthed mains lead and socket. The arrangement is sometimes described as a 'cloverleaf' connector; more officially an IEC-320 type C5 and . The two-pin type with no earth is a 'figure-of-eight' or IEC-320 type C7.

Here in the UK, double-insulated appliances can be fitted with a mains lead that has a plastic 'earth' pin - whose functions are to open the shutters on the other two holes in the socket, and to ensure correct connection of the 'live' and 'neutral' pins. But mere presence of a metal earth pin on the plug cannot be taken as evidence of an earth connection, of course!

Never seen a 'flat' three-conductor lead, or a round two-conductor lead?

Power bricks are plastic and don't need to be earthed for safety reasons. His question, which nobody has answered yet, is whether the supply NEEDS an earth to operate correctly.

yes, the 3rd hole is a ground, but while the voltage in Japan is similiar to North America (despite Japan only having 2 leads), i dont know what the voltage is in the UK. Japan runs 110v. on a 60a circuit, whereas Canada does 120.

SIXTY amps! Wow. I'm glad we have more volts in the UK.

I'd still take it that if the original mains lead was only 2-core, even if there is a 3-way connector on the power brick, then you can't have live, neutral and an earth if there's only 2 wires in the mains lead. 3 pin connectors do turn up every now and then with only 2 pins actually used but they're not very common.

As long as the original mains lead is still with the power brick, its the best indication whether its safe to use without an earth or not. Of course with a detachable lead, if examination leaves any doubt as to whether its 2 or 3 wires its easy enough to continuity test the earth pin.

UK standard domestic mains runs at 240V 50 Hz and most houses have been wired with "13 Amp ringmains" since the '60s. Our standard 13 Amp plugs and sockets have three pins; there are no standard 2-pin plugs that fit the 3-pin mains sockets - which require a third pin to open the shutters in the 'live' and 'neutral' holes before anything can be inserted into them (the earth pin being longer than the other two). Appliances which don't need an earth connection can be fitted with plugs having a plastic 'earth pin' (which presumably saves manufacturers money).

Japan's mains apparently runs at 100V, 50 or 60 Hz, and the plugs and sockets are only superficially similar to those used in the US. They seem to be rated at 10 12 or 15 Amps. (60 Amps would be pretty nasty if things went a little awry, even if a 6 KW fire might be useful). Three-pin earthed sockets are apparently not as common as might be desired. See

The UK is 240v. Actual spec is 230 +10/-6% to fall in line with Europe, but it hasn't changed from the old nominal 240.

=A0 London SW

The answer to the original poster is yes, if the power brick will accept as low as 100V andat 50 or 60 Hz, then everything will be fine.

The answer to the original poster is yes, if the power brick will accept as low as 100V andat 50 or 60 Hz, then everything will be fine.

Many thanks to all. The power brick will take the lower japanese voltage. The japanese mains plug sockets only have two pins, so they dont have an earth connection.

Peter Hucker:

The answer is no.

Japan is 100v not 110v - see

Arfa

Ringmain circuits in the UK are nominally rated at 30A, but have *outlets* on them rated to 13A. Bit of a 'picky' point, I know, but might be a bit misleading to non uk posters, the way you had put it.

Arfa

Being even more picky they're actually rated at 32 amps.

Well, the cable itself may be rated to 32 amps, and the breaker may be either 32 amps or 30 amps in an older installation, but never-the-less, this type of installation has always been known generically as a '30 amp ring main circuit' and is generally accepted as being safely rated to 30 amps to include all ages of installation.

See

Arfa

Dates from the days of rewirable fuses were it was a nice round figure. But with those you could comfortably exceed 30 amps if the load was imposed gently. MCBs react rather quicker so it's now 32 amps.

It's actually quite tricky to work out the loading in various parts of the ring since there are so many variables - the lengths and how it is run, ventilation wise. As well as where the load is actually taken. It's basically a bit of a bodge - but a very satisfactory one for today's lifestyle despite being some 60 years old in conception.

And costs you money when you stand on one and snap the pin off. Even worse when it's a wall wart.

Our UK ring mains are 6kW too, why are you surprised?

Three-pin

There is no such thing as 32A cable. It depends on where you run it and at what ambient temperature.