Hifitime,
Actually it does makes sense. Table 210.21(B)(2) Maximum Cord-and-Plug-Connected Load to Receptacle, says the maximum cord-and-plug continuous load that can be connected to a 15 amp receptacle is 12 amps. For a 20 amp receptacle the max is 16 amps. UL / CSA requires manufactures to size the cord and plug accordingly for the load of their appliance or equipment.
Example, if the continuous load of an appliance or equipment is 12 amps or less then the manufacture uses a 5-15P 15 amp plug. If the continuous load is greater than 12 amps the manufacture must use a 5-20P 20 amp plug.
That is the reason consumer vacuum cleaners only have a so called 12 amp motor, max. Most house hold convenience receptacles are 15 amp (and more than likely #14awg wire, 15 amp branch circuit) so the manufacture has to use a 15 amp plug, that is if he wants to sell any vacuum cleaners. He has to make sure the total continuous load of his vacuum cleaner does not exceed 12 amps... Pretty much the same for power amps...... Maybe a few exceptions.....
As for the difference between a 15 amp and 20 amp receptacle, the only difference is the face plate. A 5-15P plug will fit a 5-15R or 5-20R amp recept. A 5-20P plug will only fit a 5-20R amp recept.
The guts inside a 15 amp recept are the same as a 20 amp recept.
Jim
