WinterDeere
Elite Member
Source? I hope you mean due to either deterioration or improper installation. Any NEMA 5-15R is rated to handle 15 amps all day and night, when properly installed and maintained.And sadly there are many NEMA 5-15 outlets which can not really handle full power full time.
But you are going to ask 12A at 100% duty cycle. Very very few extension cords are capable.
Extension cords are rated on the packaging, when you purchase them, but everyone throws that away. Most code books use the same numbers, here's a link to the Texas code 400.5. You'll want to use column B of the table for thermoset and thermoplastic cords:
Ampacities for Flexible Cords and Flexible Cables | UpCodes
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The most common cheap outdoor cord sold today is AWG-16, which is perfectly capable of carrying 13A all day and night, so your statement about very few extension cords being capable of carrying 12A is not correct. That said, anyone would do well to always buy cords at least AWG-14 (pref AWG-12), so as to not have to worry about which cord goes to which application, down the road. Again, see column B of the Table 400.5(A)(1) I linked above.
And before anyone starts talking about column A in that table, it is for 3-phase applications, in which you have three conductors carrying current. Your regular 3-wire (2C + ground) cords fall under column B, as only two of the three conductors are carrying current.