Receptacles

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bthielen

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There have been past threads that discuss the use of 15A rated receptacles on 20A SA circuits. Am I correct that the reason this is allowed is because the 15A receptacle is built to 20A specifications and not because the 15A receptacle will reject a 20A plug? This makes sense because if a device drawing 18A was rewired with a 15A rated plug and plugged into a 20A circuit, the receptacle would not withstand the current if it were not built to handle 20A.

Assuming the above statement is true then it would be a violation to use a 20A rated receptacle on a 30A circuit regardless of the fact that it could not accept a 30A plug because the 20A receptacle is not built to 30A specifications, correct?

What guarantees that a receptacle manufacturer builds their 15A receptacles to 20A rated specifications?

Bob
 
Re: Receptacles

I think that the manufacturer is more concerned with the device carrying it's rated load and they aren't concerned with 'what if' scenarios like the one you mentioned. Are 15 and 20 amp receptacle internally the same? Probably, is it a listing requirement? I don't think so.
 
Re: Receptacles

Originally posted by bthielen:
There have been past threads that discuss the use of 15A rated receptacles on 20A SA circuits. Am I correct that the reason this is allowed is because the 15A receptacle is built to 20A specifications and not because the 15A receptacle will reject a 20A plug?
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Yes and no. Yes, the 15a receptacle will handle the 20a load. No, a 15a receptacle rejects a 20a plug to avoid attempting to power a load from a circuit not designed to handle it.
This makes sense because if a device drawing 18A was rewired with a 15A rated plug and plugged into a 20A circuit, the receptacle would not withstand the current if it were not built to handle 20A.
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Correctamundo!

Assuming the above statement is true then it would be a violation to use a 20A rated receptacle on a 30A circuit regardless of the fact that it could not accept a 30A plug because the 20A receptacle is not built to 30A specifications, correct?
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Partly. A receptacle's conficuration is more than its physical properties. It also specifies the capacity of its circuit. In either case, it is not permissable to place a 20a receptacle on a higher-rated circuit.

What guarantees that a receptacle manufacturer builds their 15A receptacles to 20A rated specifications?
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Probably a combination of UL compliance and economics. The former is because of awareness of the NEC's allowance of that use, and the latter because it's more profitable to make the conductive parts interchangeable, and only have to mold the plastic differently.

If you dissamble a 15a receptacle that has a 20a counterpart, you'll see that the contacts will accept either vertical or horizontal blades, and most likely on either side, since 250v receptacles otherwise share the same characteristics.

Also, note that voltage is not mentioned in this section of the NEC, because the rules apply equally to both 125v and 250v. See: Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits.

[ October 31, 2005, 04:21 PM: Message edited by: LarryFine ]
 
Re: Receptacles

Perhaps I completely mistook the intent of that section of the code. It wouldn't be the first time, but it might be the second.

I look at two facts:
(1) If there is only one receptacle on a 20 amp circuit, then that one can't be a 15 amp receptacle.
(2) If there are two or more receptacles on a 20 amp circuit, then one or more or even all of them can be 15 amp receptacles.

I infer that the point is that it is expected that something that draws less than 15 amps will be plugged into one outlet, and something else that also draws less than 15 amps will be plugged into another receptacle, and that the total of everything plugged in will be less than 20 amps. I know that the NEC does not (and could not) command the homeowner to use the receptacles that way. But I think the NEC allows this installation because that is how the system is expected to be operated.
 
Re: Receptacles

Charlei, I agree with your entire post, but I don't understand what it's referring to. :confused:
 
Re: Receptacles

(1) If there is only one receptacle on a 20 amp circuit, then that one can't be a 15 amp receptacle.
(2) If there are two or more receptacles on a 20 amp circuit, then one or more or even all of them can be 15 amp receptacles.
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Charlie, you are correct but I would add that this seems to be flawed logic. Why shouldn't we be allowed to put a 15 amp single receptacle on a 20 amp circuit? We can install a single 15 amp duplex on a 20 amp circuit and we may or may not ever use the second receptacle. I don't see how this is any different than having a single 15 amp receptacle on a 20 amp circuit. The device will limit the load to 15 amps.
 
Re: Receptacles

Yes, the reasoning is flawed. But I can think of no other reasoning.

The idea is to protect the 15 amp receptacle from being damaged by an overload. If you plug a 18 amp load into a single 15 amp receptacle, we can presume the receptacle might be damaged. But if that is the only receptacle on the circuit, then the 20 amp breaker will not provide any protection. So we protect that single receptacle with a 15 amp breaker.

Clearly, if there are 5 receptacles, each rated 15 amps, on a 20 amp circuit, and if you plug an 18 amp load into one of them and plug nothing into the others, you have essentially the same problem. So no, this does not make complete sense.

But I can think of no other reason for allowing 2, but not 1, receptacle rated at 15 amps on a 20 amp circuit. My only guess is the presumption that if you try to draw 18 amps from one outlet, the stuff plugged into the other outlets will draw enough to trip the 20 amp breaker. Not a certainty.
 
Re: Receptacles

I agree with the above posts, accept for- . it won't, it will simply either withstand the current, or burn up.

The OCPD will limit the current.
 
Re: Receptacles

Originally posted by bthielen:
... What guarantees that a receptacle manufacturer builds their 15A receptacles to 20A rated specifications?
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Nothing. In fact, I don't think they are exactly the same.

UL 498 will tell you more than you can stand about receptacles and testing for compliance(yawn) It's a real page turner.

About ten years ago I got curious, sawed up a 5-15R and a 5-20R, did some tests (on unsawed ones) and read UL 498. I did my tests on Fed Spec, back and side wired.

The only difference I found between the 15A and 20A is the retention force. Plugs are a lot harder to pull out of 20A recpt than they are from 15A recpt.

Intrestingly the UL test for both 15A and 20A is to overload test at 150% followed by a feed-through temperature test, followed by a retention test. The overload portion is different, 22.5A test current for the 15A recpt and 30A for the 20A recpt. The feed-through test amps are the same, 20A. And the retention force specs are the same, 3 lbf min and 13 lbf max.

So why the measured difference in retention force? Likely the 15A can be manufactured with less initial retention force and still meet UL specs. Why would the mfg bother, as noted above, the internal parts look the same? Don't know. But I'm glad they do, 15A recpts are a lot easier on the cord plugs than 20A. My inclination is to install 15A recpts unless a 20A is required - just because of the easier removal force

carl
 
Re: Receptacles

i always thought that the reasoning behind the no-single-20-on-15-amp-circuit was that the use of 20 amp devices would not often trip a 15 amp breaker, but would over time damage the wire enough for possible fires. many 20 amp devices rarely exceed 15 to 16 amps, if at all, but that is still over a safe usage for 15 amp wire. But then what do i know (not much according to some).

change for my penny please

paul :)
 
Re: Receptacles

i always thought that the reasoning behind the no-single-20-on-15-amp-circuit was
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A single 20 amp receptacle is permitted on a 15 amp circuit. See 210.21(B)(1). A single 15 amp receptacle on a 20 amp circuit is not.
 
Re: Receptacles

If you have a single device on a dedicated 20 amp circuit,the device must match the ampacity of thc circuit 20 a.Now take a 20/15 amp feed though gfci.Can to wire the 20 amp to a gfci and go to 15 amps after that,sure done in bathrooms and kitchens 24/7
 
Re: Receptacles

the exceptions prove the idea as they are very limited. the 2 applications are the only exceptions.

paul
 
Re: Receptacles

A single 20 amp receptacle is permitted on a 15 amp circuit. See 210.21(B)(1). A single 15 amp receptacle on a 20 amp circuit is not.
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This has always confused me. What are the reasons for using a single receptacle? Because you don't want any other appliances plugged into that location? Or that circuit?

If you stop and think about this, a single receptacle (15 or 20 amp) costs more than a duplex receptacle. If you're tapping off a circuit that already has duplex receptacles on it, why use a single receptacle? It's no longer a dedicated circuit and there are other devices plugged in somewhere. If you have a 15 amp dedicated circuit why would you go to the expense and use a 20 amp single receptacle? If someone, somewhere down the line, came up with an appliance that required somewhere near 20 amps to operate ( although rare I might admit) and plugged it into this 20 amp rated single receptacle that was on a 15 amp circuit it would work - but not for long.

I suppose you could also say that you could use a 50 amp range receptacle on a 15, 20, 30 or 40 amp circuit and technically be in compliance with the NEC but why would you? Wouldn't you like to think that if you replaced that range somewhere down the line that the wiring to it is rated somewhere between 40 and 50 amps?

In my opinion, single receptacles should be used for dedicated circuits only and should be sized in accordance with the wire rating feeding it so that someone (other than us knowledgeable electricians) can't plug something in at that location and create problems. Remember, many homeowners plug anything in anywhere. As long as they see a receptacle, in their mind, anything they plug in should work.

[ November 01, 2005, 05:36 PM: Message edited by: goldstar ]
 
Re: Receptacles

An individual branch circuit supplies only one utilization eequipment, so it is a bit different than the general purpose circuits we run for lighting and appliances.

Peter is correct the code says not less than meaning it can be greater than.

Although I don't think I'll live long enough to see a piece of utilization equipment with a 50 amp attachment plug that requires a 15 amp branch circuit.
 
Re: Receptacles

Originally posted by marc deschenes:
Although I don't think I'll live long enough to see a piece of utilization equipment with a 50 amp attachment plug that requires a 15 amp branch circuit.
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I agree. I just really like that code section for a few reasons: Mention that example, and see what kind of reaction you will get. It's one that really forces you to think outside the box. :D
 
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