Let's assume that everything is correct right up to the outlet. That is a 20 amp breaker, 12 guage wiring, & 20 amp rated outlet. You have 20 amps available. A rule of thumb is to have a safety net of 10%. So now you are down to 18 amps of power available. (10% of 20 amp = 2amp, 20 - 2 = 18 amp) Be sure to use an extension cord made with 12 gauge wire. If it's like most, it's only made with 14 gauge wire. 14 gauge has a rating of 15 amps before your safety 10% reduction. Any cord over 50' should be 10 gauge due to the longer distance the electricity has to travel. When the A/C compressor kicks on, it will appreciate having the 10% available to keep the voltage up temporarily. If you don't have any voltage testers, feel if the cord & plugs to see if they are warm after you've been using it. Do this after about 1/2 hr. You'll be touch a lot of metal in the AS. Don't use a cord without a proper ground. I've often plugged into the 20 amp dedicated outlet for my pool's pump. Just be sure to turn pump off 1st. I tripped the breaker a couple of times forgeting about that.
"Sometimes I wonder if the world is being run by smart people who are putting us on, or by imbeciles who really mean it." Mark Twain
AIR 22749 WBCCI 2349 NOVA TAC TN-6
1989 345 LE Classic Motorhome