Why do they allow receptacles rated at 15 amps to be used on 20 amp circuits, such as in kitchens. Has this changed in the 2002 NEC?

So far as I know, this hasn't changed. I suspect the receptacles are safe up to 40 A if wired properly. Even with a 20 A receptacle, you can't stop someone from using two 18 A devices in the same duplex at once.

To answer the why part ... a 15 amp duplex receptacle is 2 places to plug in. Therefore you could put 15 amps load on each and very happily trip the 20 amp OCPD; but it would happen safely. A single plug cannot be rated less than the OCPD because to trip the OCPD you would have to overload the device. In short, circuits usually need distribution, not capacity in one central place; hence the allowance.
As for the 2002 code ... no udea, haven't seen it yet.

You mean I can put a single duplex 15A receptacle on a 20A circuit?

Heck, I buy 20's for kitchens and baths...

Guess I'm a fool though....

Virgil,
Check out 210-21(b)(1)"A single receptacle installed on an individual branch circuit shall have an ampere rating of not less than that of the branch circuit."
(with exceptions pertaining to motors and welders).
A duplex isn't a single recep.

But why can we put a 50 Amp Recep on a 40Amp circuit??? (210-21(B)(3).

Why stop there, run your 50A 277V low bay lights off 15A twist locks....410-30(c)(2)

Probably due to unavailability
of 40 A devices

Scott,

OK, guess I got tied up in the wording again... I'll keep that in mind...

Maybe some of our Canadian counterparts will comment? I just got a job hookin' up a manufactured home from up there, all 15A devices on !%a circuits, except for those that we'd normally supply with 20A

Sparky,
Up here in the Great White North, we in the inspection department most definitely do not accept overcurrent protection rated or set at more than the ampere rating of the receptacle...except under the following condition...

The Canadian Electrical Code states:

Protection and Control of Miscellaneous Apparatus

Rule 14-600
Protection of Receptacles

Receptacles shall not be connected to a branch circuit having overcurrent protection rated or set at more than the ampere rating of the receptacle except as permitted by other Sections of this Code.

Rationale for Rule 14-600.

Receptacle configurations are standardized according to voltage and ampere ratings as shown in Diagrams 1 and 2 of the CE Code, Part I. The configurations for either locking or non-locking types are arranged to prevent connection of a load greater than the rating of the receptacle.

Intent for Rule 14-600.

We intend that branch circuit overcurrent protective devices supplying receptacles be rated not larger than the rating of the receptacles, except in specific circumstances as allowed in other Sections (eg, Rule 42-004).

Rule 42-004 states that:

Rule 42-004
Receptacles and Attachment Plugs

Where a welder is cord connected, the rating of the receptacle and attachment plug shall be permitted to be less than the rating of the overcurrent devices protecting them, but not less than the ampacity of the supply conductors required for the welder.

Rationale for Rule 42-004.
To allow for portability, certain welders need to be connected by a receptacle and attachment plug cap. This Rule provides an exception to the normal requirement of receptacle sizing, as specified in Rule 14-600, because of the nature of the connected load.

Intent for Rule 42-004.
We have determined that the ampacity of the branch circuit conductors of the welder should be the determining factor in selecting the current-carrying capacity of the receptacle. Ampacity of the branch circuit conductors has been chosen rather than the rating of the overcurrent device, because the latter is sized to accommodate short-duration inrush currents, which occur during start-up, as well as the continuous current of the welding operation.

Ok I got a question, Paulik is from the UK,and Tony Moscioni is from Canada. they both have their own codes.
Why is the NEC worried about all ' this global repositioning of the NEC' .
They keep talking about being international and working with the rest of the world on projects, but the rest of the world has their own version of the code.
Then why all the effort to change to and conform to world standards where there really isnt any ?

Are 15a GFI's legal to use on a 20a circuit?

sure they are, most specify a 20A feedthru

Sparky,
But what about not feeding through? Just using it as one duplex.

As long as it is a duples and not a single receptacle, it can be 15 amp. If it was a single receptacle on the circuit and no other outlets it would be required to be a 20 amp receptacle. See art 210.21(B)(1)&(3)