Tom Horne wrote:
On Nov 11, 6:58 pm, wrote:
On Nov 11, 5:02 pm, David Nebenzahl wrote:

On 11/11/2010 1:49 PM David Nebenzahl spake thus:
So I can only conclude that the real reason one would use a 15-amp
instead of a 20-amp outlet on a 15-amp circuit would be prevent 20-amp
loads (with their special plugs) from being plugged in, right? On a
20-amp circuit, no reason to care about this.
Is this correct? It seems to come down almost to a visual thing: if you
don't see the T-slots, don't bother trying to plug in a 20-amp device.
Forgot to add this:
The upshot being:
o It's OK to put 15-amp receptacles on a 20-amp circuit
o It's *not* OK to put 20-amp receptacles on a 15-amp circuit
Right?
The exception being a SINGLE 20 amp receptacle is apparently allowed
on a 15 amp circuit. You can find a thread here from a few weeks
back where we went back and forth on that at length. The code says
for a single receptacle, the receptacle must have a rating at least
equal to that of the circuit.

Does it make any sense? I'd say no and I sure would not wire a
receptacle that way.

If you keep reading from there you will find that the maximum
receptacle size on each circuit is laid out in Table 210-21(b)(3).

Table 210-21(b)(3). Receptacle Ratings for Various Size Circuits

Circuit Rating (Amperes) Receptacle Rating (Amperes)
15 Not over 15
20 15 or 20
30 30
40 40 or 50
50 50

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Tom Horne

210.21-B-3 is "two or more receptacles".

210.21-B-1 is a *single* receptacle on the circuit, and allows a single
20A (or 40A...) receptacle on a 15A circuit. [It also disallows a single
15A receptacle on a 20A circuit.]

When I first read this a few years ago it was hard to believe. IMHO
210.21-B-1 should be rewritten. In response to a proposal to do that the
code panel said that they don't have a problem with a single 20A
receptacle on a 15A circuit.

But it is a violation of 406.3-A.

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