Christmas lights, if made correctly, should have a fuse. These cords aren't made to handle the full 20A the breaker can. They usually cap somewhere around 3A. Nothing is stopping you from plugging a two prong 12A vacuum cleaner into them. So if you actually tried that, you'd blow the fuse in your lights before you tripped the breaker.
This is how 16 gauge extension cords should be made, too. Unfortunately, they aren't, and people light those up all the time.
Either that, or here goes Amazon, once again not vetting the shit they sell, and selling average intelligence people fire hazards.
Also, I think the lights would be perfectly happy being plugged in like that because they are LEDs. I don't know how many it would take stacked like that before you would have trouble, but I feel like it would be a lot more.
I was comparing lights two weeks ago. The sets I was looking at had 150 bulbs. The manufacturer recommended a max of 4 incandescent strings in series. For led it was 30 in series. Led only draws around 7 watts each.
Yeah and 7watts at 120 volts is only around 60mA. To get to a standard home circuitโs 15 amps (15,000mA) would take 250 LED strings. There may be some inrush current, but not of there are resistors in the led sets (every set I own has em).
Actually, many houses are built this way. My house has 15A receptacles on 20A circuits. I don't agree with it. The breaker should always be the weakest point. But the NEC (section 210.21) allows you to put 15A receptacles on 20A circuits as long as you use a duplex receptacle OR there are multiple simplex receptacles on the circuit.
This kind of thing is why code requires washing machines to have their own dedicated circuits, but you always find a duplex receptacle where the washing machine goes. It's not for your convenience. It's the most cost-effective way to pass code.
As long as the wiring is good for 20A it's fine. Also if you break open a 15A recepticle a lot of them have the 20A contacts in there as well since it's the same unit just with a different face.