Max power based on voltage

Question

I noticed that induction plates have different max power depending on the (single-phase) current voltage (there are exceptions, but this is what can be usually seen in stores)

For instance

• in Europe (220V) the power is around 2400W,
• in the US (120V) it's ~1800W and
• in Japan (100V) the max power is around 1400W

Besides possible regulations, is there an electrical reason for these disparities?

(The power depends mainly on voltage and amperage, and a lower V would imply a higher A to reach a given power. Thus, could a reason to keep a lower A be because the electric wires could heat up too much?)

Answer 1

It is based on the usual readily available circuits.

In the US, the standard residential receptacle is 15A @ 120V. That's 1800W. Actually, many devices are limited to 1500W due to 80% maximum use for continuous operation. There are larger circuits available, which would work better, but for portable appliances 15A @ 120V is the only thing you can really count on, so that is what the manufacturers make.

In Europe, voltage is roughly double - typically 220V, 230V or 240V, with varying amounts of current available. But with a typical 12A available (often more, but we'll use that as an example), that allows for 2,600W or more (depending on voltage). As a result, instead of making devices to the maximum of the circuit, they can be built to a desirable size based on usage (how much stuff you want to heat up and how fast you want to heat it).

In Japan, the voltage is 100V, even lower in the US. If devices are designed similar to the way they are designed for the US (which is a lot closer than Europe's 220V+), then 1400W or so is typical. The US numbers are actually often based on 125V. 1800W/1.25 = 1440W. There are a bunch of other variables, but that does tend towards a typical value of 1400W.

And yes, "wires heat up" is a key. Larger wires can safely handle more current, but they also cost more. So 15A-ish circuits (13A, 15A, 16A, 20A) are typical all over the place due to wire sizes, so voltage ends up determining the total power.

Since most circuits for small appliances really don't need much power, it doesn't matter much. Except for things designed to generate a lot of heat as their primary function:

• Bathrooms - hair dryers and similar items
• Kitchens - hot plates, toasters, electric grills, microwave ovens
• Space heaters

It is possible in the US to install 240V receptacles for more power, but since the typical house doesn't have any of those in the kitchen, manufacturers don't make them.

Answer 2

A typical residential/consumer can provide 13 or 15 or 20 amps. Let's call that an average of 14 amps. Volts x Amps = Watts, as a general rule of thumb. Do the multiplication on your numbers above, and you will see a pattern.

In general, if you want to sell a consumer product that has a 99% probability of not tripping a breaker, then you stay within these limits.

Answer 3

Some supplemental AV material to support the other answers. First, socket and circuit ampacity.

*Note how 20A receptacles are keyed to accept 15A plugs. Also North American electrical codes (note flags closely) allow cheaper 15A receptacles on 20A circuits, so many homes are built only with that first one. So 15A plugs are "the universal donor" and 20A plugs are almost all appliances are built to it.

A comedy bit on the fixation of 1500W in the first 2 minutes of this video.

1500W is the "80% of circuit capacity for continuous loads" point, if you pretend our voltage is 125V, which most things are rated.

And if those lower right sockets are surprising you, this cheeky video explains it. (not described: we tolerate those plugs because often-used outlets have RCD on a per-circuit basis, allowing a finer detection threshold than would be possible for a whole house).

Answer 4

First the basics: Watts = Volts x Amps. IE: 120 volts x 15 amps =1,800 watts. 240 volts x 15 amps = 3,600 watts.

Regarding the induction burners, they can be any size up to the derated current capacity of the circuit. Any device only draws what it needs. For example a 100 watt light bulb is only going to draw 100 watts even if the circuit can supply 1,800 watts.

Since most people want the highest capacity they can get in an induction burner, manufacture's usually make them at a typical circuit's capacity. The reason for the differences between countries is mostly related to voltage and circuit capacity.