Because the closest available outlet is in an awkward place, I need an extension cord in order to plug in a UPS. I already have a 50 ft medium gauge (16 gauge) extension cord in hand (safety orange, circular cross-section), but it’s really overkill since it only needs to span about 6 feet. The only other options I can find in the local hardware store are 9 ft appliance extension cords, also medium gauge but flat in cross-section. Does it make a difference which of these cords I use for the UPS? I wouldn’t have thought so, but the salesperson was rather dubious, and now I’m feeling a bit paranoid. Thanks.
It shouldn’t matter all that much. Current-carrying capacity is determined by wire gauge and the length of the cord, however, as long as what you’re plugging into it does not exceed the wattage rating of the extension cord, you should be ok. All else being equal, the shorter cord will have lower resistance. Typically, appliance extension cords are rated for 1850 W at 120 VAC in the US.
Per Q.E.D., it shouldn’t make any difference. Just make sure that if your UPS has a grounding lug that the extension cord does also.
Some long extension leads are given two current ratings, one is for when the lead is fully unwound from the reel, and the other for when it is mostly used with the rell nearly full.
The higher rating is for unwound and lower rating for on the reel.
The reason for this is that at high to medium current ratings, a cable can generate a certain amount of heat and when it is still on the reel, this heat does not dissipate as readily, hence the lower current rating.