what likely happen is a typical 15 amp receptacle is rated for only 15 amps for upto 3 hours of continious load. After 3 hours, that are rated only at 80% wich is 12 amps. With the number of plugs im a spliter, it is easy to put on 12-15 amp load on one. If the recept is on a 20 circuit, you can run up to 20 amps through a 12 (15)amp receptacle and not trip the breaker.
This is why cheap recepts melt after an extended time with a portable space heater. A 1500 watt heater draws 12.5 amps. a 12(15)amp will not carry it for long
"Live Awesome!" - Kevin Carosa