this is not my understanding of code in (at least) most of the USA. Indeed the standard practice is a 20 amp
breaker driving a number of 15 amp receptacles.
First a
disclaimer that I am an electrician, and have wired hundreds of houses and commercial buildings.
Here
that is
illegal as the devices (receptacles) are only rated for 15a, and your overcurrent protection is not sufficient. Now 5-20r as bill stated or "t-slot" receptacles can be used as a 15a
circuit (ie,
plug in things that you would normally
plug into a 15a
circuit like your waffle
iron or toaster) but the
receptacle is rated for 20a, along with the 12awg
wire that supplies it.
It is
SOP in commercial buildings to have a minimum
wire size of 12awg, yet if 5-15 receptacles are on that
circuit, it must have 15 amp overcurrent protection. If you use 5-20r's you can then use a 20 amp
breaker (unless you have to up
wire size to 10awg for one of a few reasons).
The idea of in housing of using the 5-20r on a 20 amp
breaker is to have one or two receptacles on the same
circuit with
GFCI protection in your kitchen. The "old" way of doing kitchen receptacles is to use a 5-15r and "split" it, so you have two circuits at one or two duplex receptacles (each duplex has the same two circuits). The problem is that you can't use a
GFCI and have a split duplex, so it is now
SOP to use 20a circuits in the kitchen. Personally I don't do splits at all any more, just 20a circuits. Some electricians only use 20's for GFCIs and use 15a splits for the rest. There are now more code rules in Canada about receptacles in the kitchen than any other place in a building.
You need a
receptacle for so many feet of counter space, you need receptacles on either side of a sink if there is at least a
foot of counter on the other side of the sink, you need to have one on the island (two if the island is so big or has a sink not on the
edge).
Anyways back to the OP. Yes I'd use 5-20r receptacles as my source if available. if not 15 amp circuits are fine, but some
shoebox dimmers are capable of going over 15a.