How do you use 110 volt variac for 220 volts?

To use a 110-volt variac for 220 volts, you can connect two variacs in series, ensuring each is set to half the total desired voltage. Alternatively, if your variac is rated for dual voltage, check the manufacturer's instructions to switch it to a 220-volt configuration. Always ensure the variac's power rating can handle the load and use appropriate safety precautions to prevent electrical hazards.