Which country uses 400v?

Voltage is an electrical quantity designating the potential difference between two points, frequency is the quantity designating the number of direction changes of a wavy quantity (like the number of zero crossings of an AC current, or the number bukles of an ocean wave, etc.).

Three-phase electric power (industrial applications only) CountryThree-phase voltage (volts)Frequency (hertz)Australia400 V (officially, but in practice often 415 V)50 HzAustria400 V50 HzAzerbaijan380 V50 HzAzores400 V50 HzComplete list: Three-phase electric power (voltages/frequencies) www.worldstandards.eu › electricity › three-phase-electric-power

The Nigerian Grid Code Frequency Standard is 49.75Hz and 50.25Hz while the WAPP Frequency standard is 49.80Hz and 50.20Hz . Currently West African Power Pool operates three islands due to poor frequency control.