Don't use a non-polarized extension cord with a polarized plug.

No, it’s not safe. A polarized plug has one blade wider than the other so the hot and neutral wires connect the right way. A non-polarized cord has two identical slots, so you can plug it in either way — and if you get it backwards, the device’s switch and internal wiring might stay live even when turned off.

That means the metal chassis or exposed parts could shock you if you touch them and also touch a ground. Appliances with polarized plugs (lamps, kitchen gadgets, electronics) rely on that orientation to keep the hot wire away from user-accessible areas. Flip it and you’ve bypassed that safety feature.

The hazard is real: electrocution risk, especially in damp areas or with metal-bodied tools. A cheap non-polarized cord costs a few bucks less than a proper polarized one. That’s not where you save money. Get the right extension cord — polarized, grounded if the device has a three-prong plug.