A lot of (good) US stuff is available in Japan through international online sales (Amazon).

However, most equipment purchased in Japan from the US are shipped as-is, without any change, while the current is 120 V in the US and only 100 V in Japan.

I'm struggling to assess the impact, if any, of such a difference depending on the type of equipment. The question here is to help me make the right purchase (target being, if possible, no noticeable loss of power).

There are some subtle electrical concepts that I'm not familiar with. To begin with what I (think I) know: \$V = RI\$ and \$P=VI\$ (\$P\$ for Power), that gives the famous $$P=\dfrac{V^2}R$$

My question is, what between A and B below is correct (or something else)?

A) \$R\$ is constant, Power decreases?

In this case, if \$V\$ decreases but \$R\$ is constant, obviously the Power should decrease also, proportionally to the square of the difference, for instance in Japan that would be $$P_{jp} = \dfrac{100^2}{120^2}P_{us} \approx 0.69\text{ }P_{us} $$

So for instance an US 1440 W @ 12A electric kettle would only be 1000 W in Japan (same 12A).

B) \$P\$ is constant, Intensity increases? (\$R\$ varies)

In this case, \$P\$ being constant and \$V\$ being lower in Japan, the device would suck more Amperes to reach the same Power. The ratio is $$I_{jp} = \dfrac{V_{us}}{V_{jp}}I_{us} = 1.2\text{ }I_{us}$$

The US kettle example @ 12A would consume 14.4A in Japan, which is worryingly close to the 15A "limit" of many outlets here.

My question: for instance, are my A or B assumptions below correct depending on these kinds of equipment: (please add any other equipment that make sense)

• Electric kettle (resistor => A?)
• Oven / toaster (resistor => A?)
• Food processor (motor => B?)
• Tank water pump (motor? => B?)

A lot of (good) US stuff is available in Japan through international online sales (Amazon).

However, most equipment purchased in Japan from the US are shipped as-is, without any change, while the voltage is 120 V in the US and only 100 V in Japan.

I'm struggling to assess the impact, if any, of such a difference depending on the type of equipment. The question here is to help me make the right purchase (target being, if possible, no noticeable loss of power).

There are some subtle electrical concepts that I'm not familiar with. To begin with what I (think I) know: \$V = RI\$ and \$P=VI\$ (\$P\$ for Power), that gives the famous $$P=\dfrac{V^2}R$$

My question is, what between A and B below is correct (or something else)?

A) \$R\$ is constant, Power decreases?

In this case, if \$V\$ decreases but \$R\$ is constant, obviously the Power should decrease also, proportionally to the square of the difference, for instance in Japan that would be $$P_{jp} = \dfrac{100^2}{120^2}P_{us} \approx 0.69\text{ }P_{us} $$

So for instance an US 1440 W @ 12A electric kettle would only be 1000 W in Japan (same 12A).

B) \$P\$ is constant, Intensity increases? (\$R\$ varies)

In this case, \$P\$ being constant and \$V\$ being lower in Japan, the device would suck more Amperes to reach the same Power. The ratio is $$I_{jp} = \dfrac{V_{us}}{V_{jp}}I_{us} = 1.2\text{ }I_{us}$$

The US kettle example @ 12A would consume 14.4A in Japan, which is worryingly close to the 15A "limit" of many outlets here.

My question: for instance, are my A or B assumptions below correct depending on these kinds of equipment: (please add any other equipment that make sense)

• Electric kettle (resistor => A?)
• Oven / toaster (resistor => A?)
• Food processor (motor => B?)
• Tank water pump (motor? => B?)

A lot of (good) US stuff is available in Japan through international online sales (Amazon).

However, most equipment purchased in Japan from the US are shipped as-is, without any change, while the current is 120 V in the US and only 100 V in Japan.

I'm struggling to assess the impact, if any, of such a difference depending on the type of equipment. The question here is to help me make the right purchase (target being, if possible, no noticeable loss of power).

There are some subtle electrical concepts that I'm not familiar with. To begin with what I (think I) know: \$V = RI\$ and \$P=VI\$ (\$P\$ for Power), that gives the famous $$P=\dfrac{V^2}R$$

My question is, what between A and B below is correct (or something else)?

A) \$R\$ is constant, Power decreases?

In this case, if \$V\$ decreases but \$R\$ is constant, obviously the Power should decrease also, proportionally to the square of the difference, for instance in Japan that would be $$P_{jp} = \dfrac{100^2}{120^2}P_{us} \approx 0.69\text{ }P_{us} $$

So for instance an US 1440 W @ 12A electric kettle would only be 1000 W in Japan (same 12A).

B) \$P\$ is constant, Intensity increases? (\$R\$ varies)

In this case, \$P\$ being constant and \$V\$ being lower in Japan, the device should suck more Amperes to reach the same Power. The ratio is $$I_{jp} = \dfrac{V_{us}}{V_{jp}}I_{us} = 1.2\text{ }I_{us}$$

The US kettle example @ 12A would consume 14.4A in Japan, which is worryingly close to the 15A "limit" of many outlets here.

My question: for instance, are my A or B assumptions below correct depending on these kinds of equipment: (please add any other equipment that make sense)

• Electric kettle (resistor => A?)
• Oven / toaster (resistor => A?)
• Food processor (motor => B?)
• Tank water pump (motor? => B?)

A lot of (good) US stuff is available in Japan through international online sales (Amazon).

However, most equipment purchased in Japan from the US are shipped as-is, without any change, while the current is 120 V in the US and only 100 V in Japan.

I'm struggling to assess the impact, if any, of such a difference depending on the type of equipment. The question here is to help me make the right purchase (target being, if possible, no noticeable loss of power).

There are some subtle electrical concepts that I'm not familiar with. To begin with what I (think I) know: \$V = RI\$ and \$P=VI\$ (\$P\$ for Power), that gives the famous $$P=\dfrac{V^2}R$$

My question is, what between A and B below is correct (or something else)?

A) \$R\$ is constant, Power decreases?

In this case, if \$V\$ decreases but \$R\$ is constant, obviously the Power should decrease also, proportionally to the square of the difference, for instance in Japan that would be $$P_{jp} = \dfrac{100^2}{120^2}P_{us} \approx 0.69\text{ }P_{us} $$

So for instance an US 1440 W @ 12A electric kettle would only be 1000 W in Japan (same 12A).

B) \$P\$ is constant, Intensity increases? (\$R\$ varies)

In this case, \$P\$ being constant and \$V\$ being lower in Japan, the device would suck more Amperes to reach the same Power. The ratio is $$I_{jp} = \dfrac{V_{us}}{V_{jp}}I_{us} = 1.2\text{ }I_{us}$$

The US kettle example @ 12A would consume 14.4A in Japan, which is worryingly close to the 15A "limit" of many outlets here.

My question: for instance, are my A or B assumptions below correct depending on these kinds of equipment: (please add any other equipment that make sense)

• Electric kettle (resistor => A?)
• Oven / toaster (resistor => A?)
• Food processor (motor => B?)
• Tank water pump (motor? => B?)