Why are there 15- and 20-amp receptacles?

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Actually not a dumb question, as I trust you'll see.
Reading through the thread above about using 15-amp outlets on a 20-amp kitchen circuit, and even following the discussion to an external forum (Mike Holt's) raises this question in my mind: why do we have outlets in both ampacity ratings?
From what I gather from the Holt forum, which included much back-and-forth about UL ratings (and an actual email response from UL itself), both 15- and 20-amp outlets are capable of handling 20 amps, both through the receptacle blades and through the pass-through between the sets of screw terminals. So it's not an issue of overloading the device itself. A 15-amp outlet will work fine on a 20-amp circuit with a 20-amp load.
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.
[Of course this only applies to North America and places with similar-type electricity: dunno how this all plays out in the UK, for instance.]
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David Nebenzahl wrote: ...

...
Should one not say "obviously"????
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On 11/11/2010 1:49 PM David Nebenzahl spake thus:

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?
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That is correct regarding multiple outlets on a branch circuit
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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.
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On 11/11/2010 3:58 PM snipped-for-privacy@optonline.net spake thus:

>> o It's *not* OK to put 20-amp receptacles on a 15-amp circuit

Riiight, the exception to the rule. Ugh.

I'm with you there.
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Are you asking what is reasonable practice, or what would be safe?
If everything else is to code on a 15 amp circuit, it should have a 15 amp fuse/breaker and everything downstream should be able to handle at least that much. So, even if you plug a 50 amp load into the outlet, it SHOULD pop the breaker/fuse before anything really bad happens. The question is, how much faith do you have that everything other than the outlet is correct and in good shape.
Not that you can't start a fire with 15 amps...
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On Nov 11, 6:58pm, snipped-for-privacy@optonline.net wrote:

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
-- Tom Horne
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Tom Horne wrote:

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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news:5e494783-7958-47c9-b52d-
<stuff snipped>

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
__________________________________________________________
Thanks for clearing that up, somewhat. (-:
It makes a lot more sense to allow a 15A receptacle on a 20A circuit but not vice versa. If you plug in a 15A device into a 20A circuit, so what? Not true of the reverse and from what I can tell, the NEC frowns on connecting loads larger than the capacity of the circuit. It would also explain why 15A receptacles probably do pass-thru 20A with no problems via the screw terminals, but couldn't pass 20A through the plug connector blades, which I assume are made of thicker metal in the 20A receptacles. I actually just bought a mix of both so I'm going to go see how they are marked and report back.
Of course, all of what I just wrote isn't valid if it's true you can use a 50A receptacle on a 40A circuit. Is that line correct? Why would they allow you to use a 50A receptacle on a 40A circuit if they don't allow that combo at lower amperages?
-- Bobby G.
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Because there are no 40A receptacles.
Wayne
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wrote:

Did there used to be and the mention in the NEC is a grandfathering sort of thing? What's the point of mentioning in the NEC something that doesn't exist.
-- Bobby G.
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snipped-for-privacy@optonline.net wrote:

210.21-B-1 allows that. It is a general permission, not specific to a 20 on a 15.
But a 20A receptacle on a 15A circuit is a violation of 406.3-A and can be tagged. The rule for receptacles would be expected to be in the article on receptacles, which is 406.
There remains a hole - you can install a single (not a duplex) 20A non-grounding receptacle on a 15A circuit that has no ground if it is the only receptacle on the circuit. Rather limited application. And you would have to find a single 20A receptacle without a ground.
--
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I'm surprised that you're now back to saying that the NEC clearly does not allow a 20 amp receptacle on a 15 amp circuit. As I recall, a month ago, you provided us with the link to the actual discussion among the writers of the NEC on that specific issue and it was clear that they were saying that 210.21 B1 allows it and they made no reference to 406 disallowing it. Or did I miss something from back then? IMO, 406 isn't clear on that and while you could interpret it that way, it's strange that the NEC code guys weren't talking about it.

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snipped-for-privacy@optonline.net wrote:

The thread was "15A outlets on 20A circuits" which started 10-12.
I consistently said in that thread that 406.3-A prohibits a 20A receptacle on a 15A circuit and could be used to tag the installation. My last post was "as I said, IMHO a 20A receptacle on a 15A circuit can be tagged under 403.6-A [should be 406.3-A]".
I did say that the code panel for 210 did not agree and that 210.21-B-1 allows it.
If I was an inspector I would argue (as I did above) that 210.21-B-1 is a general provision but that 406.3-A is specific to 15A circuits. The specific rule trumps the general rule. And the appropriate place to look for the rule is in the article on receptacles, which is 406.
IMHO 406.3-A clearly prohibits a 20A receptacle on a 15A circuit. I believe gfretwell agreed.
--
bud--

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That is a stupid rule and a poor observance by the code enforcement community. A 20 amp receptacle on a 15 amp circuit endangers no one, as mentioned the circuit breaker will detect any overload and trip, now a 15 amp receptacle on 20 amp circuit is dangerous and will eventually brown out. Roy Q.T. E.E.Technician
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That's right it's me, I control my demons. Roy
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On 11/13/2010 11:16 AM, Proteus wrote:

At least you're not YELLING! 8-0
TDD
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wrote:

At least you are not INSULTING! (cancelled due to rain)
ROY STEPPED OUT I GOT THIS NOW:) HAVE A GREAT WEEKEND! PATECUMSEH
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On Sat, 13 Nov 2010 14:32:26 -0600, The Daring Dufas

Please don't feed the trolls.
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