Wiring typically has ~100% safety margin built in, however this cannot be counted on. If your wiring takes 15A, it should in theory handle 30A safely. HOWEVER, any nick or sharp bend in the wiring can increase resistance in the wiring, or even worse decrease the electrical resistance of the cable insulation. Heat also amplifies this problem, so an overloaded wire handling 30A in the cold of a Siberian winter might not handle it in a sweltering summer.
The safety margin is there for safety, just like how skydivers have a reserve chute, it doesn't mean you should rely solely on your reserve day after day.
Personally I would never overload house wiring, it's just not worth the risk. However I do occasionally overload extension cords (they have the same ~100% safety margin) for certain quick tasks where the cable doesn't heat up, but I'd certainly never push a 15A cable to 30A . . . I got close to something similar, a 14A appliance on a 8A extension because I was a moron and didn't read the label.
Also it's good to note that, not all cabling or extensions have the 100% safety margin, this margin is in place so that any defective products should still meet the minimum requirement.
The safety margin is there for safety, just like how skydivers have a reserve chute, it doesn't mean you should rely solely on your reserve day after day.
Personally I would never overload house wiring, it's just not worth the risk. However I do occasionally overload extension cords (they have the same ~100% safety margin) for certain quick tasks where the cable doesn't heat up, but I'd certainly never push a 15A cable to 30A . . . I got close to something similar, a 14A appliance on a 8A extension because I was a moron and didn't read the label.
Also it's good to note that, not all cabling or extensions have the 100% safety margin, this margin is in place so that any defective products should still meet the minimum requirement.