I understand that Japan uses 100V and the maximum power available is around 1400W. Currently, my computer runs on a 1300W PSU. When I move over there, I'll need to downgrade, so I'm wondering about the power usage of other appliances. After accounting for my computer's 850W requirement, I'll have about 550W left. However, on PC Part Picker, it looks like I'll be using around 750W with my cam, mic (XLR), and monitors

I will be running 1440P 170Hz monitors from MSI Here are the monitors (There will be 2): MSI G272QPF 27.0" 2560 x 1440 170 Hz Monitor

Here are the peripherals

  • Stream Deck
  • scarlet solo XLR interface
  • Fifine K688
  • Steelseries Mouse
  • Ducky One 2 RGB TKL
  • Logitech X-140 4 W Speakers

PC Specs after downgrading

  • Ryzen 7 5800X
  • MSI MPG X570S Carbon Max Wifi
  • G.Skill Trident Z Neo 128GB 4X32GB
  • MSI Gaming X Trio 4080
  • Samsung 980 Pro 2TB
  • WD Black SN850X 4TB
  • MSI MAG A850GL PCIE5 850 W 80+ Gold Certified Fully Modular ATX Power Supply

Here are case stuff like AIO, fans:

  • MagniumGear NEO QUBE 2 Infinity Mirror ATX Mid Tower Case
  • EK-Nucleus AIO CR360 Lux D-RGB 72 CFM Liquid CPU Cooler
  • EK Vardar X3M 120ER 67 CFM 120 mm Fan X6

Will this Trip if I use the shower or Oven so something that would need to be used for cooking.

  • 4
    The 1400w is probably for one single circuit, not the whole house, same as US with about 1800w one circuit(15 amps). The 1300w PSU is maybe the output, not the input.
    – crip659
    Commented Mar 8 at 13:48
  • 1
    Please revise to punctuate your sentences properly so you're more readable. Also revise your title to ask a clear, specific question. See How to Ask and take the tour.
    – isherwood
    Commented Mar 8 at 14:19

1 Answer 1


There are two key issues here:

Actual Usage

A "1300W PSU" doesn't necessarily use 1300W. In fact, it is likely that most of the time it is using far less, depending on demands of CPU, motherboard, drives, expansion cards, etc. Even if you never use 1300W, a large power supply can still be a good thing to have. If it is designed well then it will be less likely to overheat or have other problems at 500W than a 500W power supply would have.

Many other devices are also rated for maximum possible usage rather than typical usage. Also keep in mind that everything inside the computer case, plus anything powered from it (typically USB-connected devices) is all included in the power supply usage. The exceptions are devices that have their own power supply connected - typically monitors and printers. Monitors will generally use close to their total power rating. Printers will often be rated for different power levels for "sleep" vs. "printing".

The only practical way to tell how much power you need is to measure how much you use with a Kill A Watt like this one from Amazon:

Kill A Watt

or a similar device. Plug everything into it. Run your favorite programs and see what it shows.

The solution to a problem of "computer and air conditioner/cooktop/whatever on at the same time trips a breaker" is normally going to be dedicated circuits. A dedicated circuit is added for one specific use. Depending on where you live (especially if you are in a rental where you have to have someone else do the work and you have to agreement of your landlord) it may not be practical to add a dedicated circuit and then it becomes a game of figuring out where you can plug in different things to make it all work.

Circuits vs. Service

In most setups there are two different "totals" available - circuit and service. The circuit value is how much you can provide to any device or group of devices sharing that circuit. In the US, this is typically 15A or 20A @ 120V for the standard receptacles, but larger circuits (e.g., 30A @ 240V for a water heater or clothes dryer, 40A @ 240V for an oven, etc.) are available. The service size is the maximum your utility agrees to provide. In the US for new construction that is typically 200A @ 240V, but sometimes more than that. But many older houses have smaller service feeds, and it varies a lot around the world.

In a quick search, it looks like while the standard residential service is 100V, there are at least some places that have 100V/200V available in a setup similar to the US 120V/240V system. The service size seems to range anywhere from 30A on up to 75A, possibly more.

If your total usage goes over the service size then you will trip the main breaker and the entire house loses power. You want to avoid that if at all possible. A single computer (even a fancy gaming rig) shouldn't be enough to make the main breaker trip. A rack full of Bitcoin mining computers, each on a separate circuit, could do that. So can various combinations of ordinary stuff together with:

  • Tankless electric hot water
  • Electric vehicle charging
  • Electric resistance heating
  • Electric oven + cooktop

In a typical house these are non-issues until you start replacing old lower-power electric (e.g., tank with tankless) or non-electric (gas with electric) appliances, or add new big stuff (EV charging). In the US this is managed using an NEC Load Calculation. There is likely an equivalent in Japan, but I don't know what it is.

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