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I have a convection microwave oven that has a normal 15A 100V plug. I can only conveniently access a 20A 250V outlet, which looks like this: The outlet. (I am located in Taiwan).

Are there any safety issues with finding a way to connect them? What should I look for in an adapter?
By the way, as a layperson, how does this this kind of thing even work in theory? Is it that 20A of current comes out of the wall, and so it'd be dangerous for a 15A appliance to handle it, or is it that the the appliance draws up to 15A of current, and the wall can provide up to 20A? How does the voltage come into play?

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  • 12
    The "20 A" means that receptacle can supply a maximum of 20 A. The appliance is said to "draw" current and the appliance, when working properly, draws an amount less than 20 A that it is designed to draw. The circuit will not force 20 A into the appliance that is designed to draw 10 A. However, the voltage specified is exactly what the circuit "delivers" and is not the maximum it can deliver. An appliance designed to have power delivered to it at 100 V cannot accept power delivered at 230 V. Aug 6 at 9:44
  • 1
    Related (same situation, though a different perspective on the question): Why would replacing this 240 V outlet with a 120 V outlet trip my breaker?
    – TylerH
    Aug 6 at 15:14
  • How does the voltage come into play? ... voltage is the "pressure" that forces current to flow ... increasing the applied voltage will increase the amount of current that will flow in a circuit, possibly beyond the capacity of the appliance
    – jsotola
    Aug 6 at 19:53
  • Related - 100V AC is a Japanese main island standard. They also have split frequency, with half the country at 50HZ and half at 60HZ Check that your appliance can take the local AC frequency as well, before starting. Otherwise you need a replacement microwave.
    – Criggie
    Aug 7 at 2:27
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    These 250V recepticles are used almost exclusively for air conditioning units in Taiwan, and unless you own the place your landlord likely won't like you changing that. I'd get an extension cord (a good quality one)
    – Setsu
    Aug 8 at 6:53
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No. That is a NEMA 6-20 receptacle. Your NEMA 5-15 appliance is specifically designed to not plug into it.

Because it would destroy the appliance if you did.

That is why the system of plugs works like it does.

enter image description here

Yours is a Taiwan derivative that does not allow multi-amperage, so it does not have the T-shaped L2 phase.

Anything that plugs into the wall needs a specific voltage. The device automatically draws the right amount of amps that it needs.

Your appliance needs 100-120V. There is nothing available at this socket except 200-240V. There is no affordable way to convert the output here into what you need.

DO NOT use a common stepdown (auto)transformer! This receptacle has no access to neutral. The market is absolutely flooded with "step down (auto)transformers" which will seem to work but will place your microwave's neutral at 120V from ground, a dangerous situation.

If you want to, it's probably possible to have an electrician re-wire the circuit so the socket can be changed to what you need.

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    "Anything that plugs into the wall needs a specific voltage" lacks a final range. For many modern devices, that range can be wide (e.g. 100-240V for the charger of my PC). For the question's 100V device, that range is much narrower, perhaps 90-110V.
    – fgrieu
    Aug 6 at 17:04
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    @BlueRaja-DannyPflughoeft: In Japan, the standard voltage is nominally 100 V. A number of consumer devices (including those with large transformers like microwave ovens) are specifically designed for 100V, and seriously misbehave on 120V, especially at the high end of the tolerance.
    – fgrieu
    Aug 6 at 18:23
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    @Keeley neutral needs to be near earth voltage in order to be safe. You can only get away with a "hot" neutral if the appliance is double insulated. Microwaves generally aren't. Aug 6 at 21:39
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    @Joshua Welcome to DIY stack exchange. Your plan requires an isolating transformer, which is a black swan on the Taiwan market (and for that matter US Amazon), which is 99.9% glutted with those cheapie stepdown transformers, which are autotransformers and are not able to isolate. That's why I'm studiously avoiding sending OP off to buy a transformer. Aug 6 at 22:57
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    A true transformer could safely allow plugging your microwave in. However, such a transformer probably costs more and weighs more than your microwave. Aug 7 at 1:47
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At the moment NO.

You have three choices:

  1. sell that device and purchase one that is rated 230V.

  2. get a 230 to 110 transformer.

  3. replace that supply and socket with one of 110V.

Which of these is most convenient is down to your circumstances.

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    @user253751 those transformers are easily available, about 20cm by 20 cm by 30 high - usually in yellow protective boxes for use on industrial sites and rated to 3kW . I have one to power some of my woodworking tools.
    – Solar Mike
    Aug 6 at 13:44
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    20x20x30cm of mostly solid metal is indeed quite big and heavy
    – user253751
    Aug 6 at 14:17
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    Also, if OP attempts a search for a transformer, they have a 98% chance of finding one that is dangerous -- the universal red "step down transfomer" a huge number of which are actually made in Taiwan. That doesn't work to step down center-neutral 240V, because it will be trying to take neutral reference from a phase - moving output neutral 120V from ground. OP would need an isolating transformer and those are obscure enough that they won't be affordable. Aug 6 at 18:13
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    @SolarMike Problem is, if you tell a person in Taiwan to go to the local shop and grab a transformer that is sold in "hundreds of locations", they won't find any of those in Taiwan. They will find PLENTY of the red ones that will kill you. Those yellow ones would work, but are unobtanium outside the UK. Aug 6 at 18:48
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    Given the comment of @jay613, are extension cords allowed in Taiwan? Is there a 100 V receptacle near enough that you could use an extension cord? You would want one that is rated for the current that this oven draws. Aug 6 at 21:23
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The other answers are all correct, you cannot, but they don't address your question of how this works in theory, so I'll take a stab at it.

You can think of voltage sort of like water pressure, and amperage sort of like the velocity of water flowing. Right now in that socket is 250V worth of pressure. Since nothing is connected, no amps are flowing. That 20A is the max amount of amount of flow the socket can support till things in the socket start breaking.

Your microwave is only rated for 100V of pressure, so if you hooked it up to the 250V, it'd be like hooking a garden hose to a fire hydrant: the pressure would be too much and it burst, probably allowing no current through, though it might allowing unrestricted amps until it exceeds 20A worth of flow and the breaker would trip.

The 15A on your mircowave means that it is guaranteed to allow 15A or less to flow under normal voltage and operation. Most devices work sort of like a valve, when off allowing no amps to flow, and under different conditions allow more or less amps to flow. Generally, as long as the amps required by a device is less than the max allowed by your power source, you're fine.

This is all governed by Ohm's law, which if you google you can find far better examples, explanations and analogies than I could come up with.

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  • Having the receptacle's max ratings embossed on the FRONT seems unwise. Likely to cause confusion such as this to naive end users, and not likely to help electricians by being on the front. I wonder if Taiwanese Panasonic 100V receptacles also have "250V" embossed on the front? Or if in fact they are manufactured differently and are rated for 100V?
    – jay613
    Aug 6 at 16:37
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In addition to the good accepted answer, please note 2 things:

First:
the ratings of the outlet socket and plug cable are not the most important deciding factors. What's more important is the actual voltage supplied to the socket, and the actual voltage range accepted by the appliance. If a socket is rated at 250V, you could actually have either 220V or 110V wiring connected inside it, so if you have a way to measure it, you might find the voltage to be suitable for the device after all. (But be careful, it could cause serious injury or death if you make a mistake while doing it).
As for the appliance, if it's fitted with a 100V cable, it usually does not accept 220V, but you should not get that information from the cable itself. The machine should have a nameplate similar to the image blow, that tells you what voltage and frequency it accepts.

enter image description here

Second:
Most countries that have 200 to 240 V outlets (like Europe) operate at an AC frequency of 50 Hz, and most outlets that provide 100 to 120 V usually have an AC frequency of 60 Hz (like North America).

According to Wikipedia, Taiwan has both 110 V and 220 V residential voltages, and both operate at 60 Hz, so the frequency should not be an issue of you (but the voltage definitely is).

But for readers in other countries, it is not recommended to use a microwave designed for one frequency in a country that has the other. One reason is that the timer clocks in some microwaves depend in the frequency to count the cooking time. Using the wrong frequency can cause the clock to run faster or slower than it should.
In other words, when you cook for 5 minutes it actually stays for 6, or the other way around.

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If the outlet is supplying 230V, you cannot connect a device rated for 120V without bad things happening; the device would almost certainly be destroyed, and very likely start a fire.

The 20A rating on the circuit is the most current it can safely deliver to a load; if a load draws more than the rated limit, excess heat will build up in the circuit's wiring which could start a fire. The circuit should have protection against this in the form of a fuse or circuit breaker which should trip before any damage occurs in the circuit. In the context of your question, that's 20A.

The 15A rating on the appliance indicates the peak load it could impose on a circuit; in other words, if the circuit can't deliver at least 15A, you'll probably trip a circuit breaker or blow a fuse if you try to use the appliance.

You can connect a 15A appliance to a 20A circuit, with caveats. There is no issue with doing so for any appliance in good working order. A properly engineered appliance should have internal circuit protection so that any internal fault should trigger the internal protection and not rely on the external circuit for over-current protection. If it's a cheaply-made appliance, it might not have such internal protection, so connecting it to a circuit with a very generous current rating could be risky, but then it could be risky connecting a cheaply-made appliance to any circuit.

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VERY DANGEROUS, but you could in theory connect the 110 hot lead to 1 hot side of the 220, and the 110 neutral to the 220 ground, and leave the 110 ground unconnected" but now the chassis will be floating and there will be current on the ground--BOTH VERY BAD! DON"T DO IT.

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  • Aside from the trivial side-effect of killing the operator, this is also almost guaranteed to cause a ground-fault trip on your DB. Unless your whole building does not bother with ground-fault detection, in which case.... How are you still alive?
    – PcMan
    Aug 8 at 15:29
  • There are old buildings in Taiwan, but given the proper NEMA socket for 240V is installed, thankfully the OP might be safer.
    – Nelson
    Aug 9 at 3:32

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