Does the NEC allow 15 amp outlets to be

[Alan Tolchinsky]

used in a 20 amp circuit? I thought I read this here. My house is wired like that so either it's correct or the inspector missed it. Anybody know the NEC on this? Thanks!

[Rob Damon]

If you only have one 15Amp receptacle on the 20Amp circuit breaker, the answer is no. You must use a 20Amp receptacle (per NEC 2002,210.21(B)(1).

If you have multiple 15Amp receptacles on the circuit (like your house), then yes you can protect the 15 amp receptacles with a 20Amp circuit breaker. (per NEC 2002, 210.21(B)(3).

Rob

[Rob Will]

Good answer Rob, and welcome to the creek!

Rob

[Chris Friesen]

If you only have one 15Amp receptacle on the 20Amp circuit breaker, the answer is no.

Note, however, that a standard duplex outlet (that can take two plugs) counts as two receptacles for the purpose of that rule.

[Rob Damon]

Receptacles on a common strap (i.e. duplex, or even triplex) count as a single 180VA receptacle and our local AHJ's interpet that as a single receptacle. It would be open to your local AHJ to determine if they consider two receptacles on a single strap as being two receptacles.

It would also negate the intend of allowing it. The code assumes that it is unlikely on a general purpose branch circuit that you would put an individual load on a single receptacle that would use the entire 20Amps, thus allowing you to use multiple 15Amp outlets on a 20 amp circuit. The 15 amp receptacle is still only listed for 15amp. If you were to break the tap and split wire the duplex receptacles each receptacle you may be able to convence the AHJ you have "two" receptacles" but unforcunately ours won't buy into it. And they have the ultimate say in the matter. Plus we are always behind the curve here in the Old Dominion as they just approved the 2003 IBC which uses the 2002 NEC last year.

Oh yeah ,glad I found this place.

Rob

[Dave MacArthur]

Remember that there is a huge diff between a "20 amp circuit" meaning a circuit WIRED with 12 ga wire rated to carry 20 amps, and a 15 amp receptacle circuit, run on 14 ga wire, but protected with a 20 amp CB...
If you go with the mindset that the CB is there to protect the wiring, and that the design of the receptacle is INTENDED to inform the user of the limits of the wiring and allow them to make full use of the rated amperage, then I see no reason why you would put 15A plugs on a 20 A circuit... I know it is common, but 50% of threads on these forums talk of manufacturers cutting corners and going cheap where allowed to save 10$. I would use 20A receptacles myself. Not an electrician, but have done several houses. It sounds like maybe Rob or Chris are electricians, if so, is there some good reason why you would WANT to put 15A recept. on a 20A circuit, besides pinching pennies? Thx!

[Rob Damon]

Dave, I am actually a senior electrical at a international Architectural/Engineering firm and I have been designing electrical systems since 1979. Most of it has been heavy industry/manufacturer/commercial/government stuff. Occasionally, I get a few multi-family mixed use buildings to work on, which is the only place I allow a contractor to use a 15amp receptacle, but not by choice. It is always an owner wanting to "pinch a few" extra pennies. The owner asks "Does it meet Code??", and the answer is "yes, but I don't recommend it", and they accepted it anyway as a part of the "value engineer" that seems to happen more and more these days.

That is the only way I would let them be used. In a house they are fine. In a workshop where you regularly plugging various sized loads, I would stick with 20Amp receptacles, they are not really that much more in the scheme of things.

Rob

[Tom Veatch]

... In a workshop where you regularly plugging various sized loads, I would stick with 20Amp receptacles, they are not really that much more in the scheme of things....

This post causes me to think back, and I don't recall ever seeing anything equipped with the NEMA 5-20 plug - one vertical and one horizontal blade - that would physically require the 20amp receptacle.

I wired the 120v circuits in my shop with 20amp circuits including the 5-20 receptacles but every 120v device I use has the 5-15 plug (2 vertical blades).

[Steven Wilson]

Festool CT-22 vacum is one, the Furman IT-20 II Balanced Power Conditioner in my recording Studio is another. There are a few products out there but it is rather rare.

[Rick Christopherson]

Receptacles on a common strap (i.e. duplex, or even triplex) count as a single 180VA receptacle and our local AHJ's interpet that as a single receptacle. It would be open to your local AHJ to determine if they consider two receptacles on a single strap as being two receptacles.

Unless your jurisdiction specifically nullifies the article (which they could do if they wish) they cannot alter the definition of a receptacle. A duplex receptacle is just as it states--it is “duplex”, which is defined as “two”.

They could state that a single duplex receptacle does not qualify to be placed on a 20 amp circuit, but they cannot alter the definition of the device itself. Duplex is Duplex, and that is not open for alteration by local jurisdictions.

My guess is that you ran into an overzealous inspector that made this interpretation, but it is not necessarily the local code.

Your idea of demanding 20 amp outlets is rather silly and shortsighted. The purpose of the device is to prevent an appliance that requires 20 amps from being connected to a 15 amp circuit. So unless you are in an environment where 20-amp appliances are common, there is little need to worry about the configuration of the outlet.

If you were an electrical engineer then you would know that the current carrying capacity of the outlet itself has little to do with this rule. Nevertheless, that is the assumption that you are making.

[Alan Tolchinsky]

Thanks all for the advise. I think I'll take Rob's advise and just use the 20 amp outlets anyway.

[Rob Damon]

What is sometimes overlooked is Article 90..

90.1(B) "This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily effecient, convenient, or adquate for good service or future expansion of electrical use."

and

90.1(C) "Intention. This Code is not intended as a design specification or an instruction manual...."

Most of the electrical engineers I have worked with consider the NEC as a minimum of what is required and we design to a "higher standard of care" than the bare minimum, unless overruled by an owner.

Most of the installation I design for are industrial/commercial not residential, as I stated, and most owners at that level have established design criteria that exceeds the minimum Code requirements, mostly based on insurance (FM) carrier requirements. So 20amp is the standard from what I have experienced. When doing multi-family residential we do allow 15amp receptacles. Not a problem, with a few exceptions.

The other thing to consider is that factory installed cord and plugs are UL listed through the manufacturer testing procedures and not through the NEC. Thus, as most equipment it most likely tested for intermitted use, thus the cord/plug can end up with a lower rating than what you might expect to see, thus have a NEMA 5-15, as oppose to a NEMA 5-20.

Had I realized this was going to be a long drawn out discussion, debating my design ability of 28 years "If you were an electrical engineer then you would know", I would have refrained from responding............I will do so in the future......as it relates to "electrical issue" and confine my comments to wood working.

Sorry,

Rob

[Jim Thiel]

Yet another intelligent poster with a thoughtful and timely response gets cracked in the head.

I'm sorry Rob. I found your information to be helpful to the question and general electric work. Thank you for sharing your expertise.

Jim

[Greg Funk]

Your idea of demanding 20 amp outlets is rather silly and shortsighted.

I wish we had a silly and shortsighted engineer like Rob 4 yrs ago when we built our house. All of the 110V outlets in my shop are 15A so I don't have anywhere to properly plug in my CT22.

Rob: Please don't hesitate to post on electrical issues in the future. It is always useful to everyone to have someone knowledgeable sharing their experience.

Greg

[Chris Friesen]

It sounds like maybe Rob or Chris are electricians, if so, is there some good reason why you would WANT to put 15A recept. on a 20A circuit, besides pinching pennies? Thx!

I'm no electrician, but I do have an engineering degree and recently rewired my garage/shop. (In the process doing a lot of research.)

Basically penny-pinching is the main reason I can think of why you wouldn't go with 20A receptacles on a 20A circuit. Given that generally 20A is only available in commercial grade and thus costs 6-7 times as much as a cheap 15A, the difference can add up if you're doing a lot of outlets.

When I replaced the receptacles in my house I went with the cheap ones most places, but used commercial grade ones where they'd be used a lot (kitchen & bathrooms). The garage is all commercial grade except for the ceiling outlet for the door operator, and the new circuits I put in are all 20A.