I had to relocate the microwave (and the cart on which it sits) to the next room for a day or two while we have the kitchen flooring redone by an experienced friend. My wife still needs to use the microwave rated at 14.0 amps. I require an extension cord to reach the wall outlet. I have a 50-ft outdoor extension cord rated for 300V, and it is a 16 AWG, 3-conductor cable. There is no indication of max amps, but surely some EE can use this information to tell me if this extension cord safe to use for this application? (I am in the US, so I’d assume 120V, 60 Hz power supply.)
You need a #14 AWG cord to safely do this. Often listed as “heavy duty” or “appliance” extension cords. Keep it as short as possible, 12-15 feet if possible. (Or look for a different outlet that is closer to the temporary location.)
You can’t get a #16 AWG cord rated to carry this, no matter how short you make it. (But there is a safety factor built into AWG ratings, so a #16 extension cord would probably work, especially as a microwave isn’t typically on for more than a few minutes.)
Rule of thumb is 14 ga for 15 amp circuits and 12 ga. for 20 amp which covers most residential circuits/uses. So 16 gauge would never be rated for 14 amps.
Not questioning you, but why can the 12 gauge wires in the walls of my home carry 20amps, but the extension cord with the same sized wire carry only 15?
The rating for extension cords also includes the plug and socket. That, combined with the thicker jacket, derate that current-carrying capacity of the cable.