210.21(B)(3) says "when connected to a branch circuit supplying 2 or more receptacles oar outlets...." If there is only 1 receptacle neither 210.21(B)(3) or table 210.21(B)(3) apply. As I wrote, and you deleted, "Table 210.21-B-3 applies to 2 or more receptacles"
But I agree it is a stupid idea (allowed by the NEC).
UL 20 (1991), the standard for wall switches, which I have, has extensive testing. The testing includes
- 10,000 operations at rated voltage and current
- 10,000 operations at rated voltage and current with a power factor of about 0.8 (inductive load)
- 10,000 operations with an incandescent light load (inrush greater than rated current The switches must survive intact and fully functional.
I don't really think that receptacles, if UL listed, have a less rigorous testing and certainly can't fail the tests with a "fire contained in the device".
Not to say I am fond of cheap receptacles.
210.21(B)(3) says "when connected to a branch circuit supplying 2 or more receptacles or outlets...." If there is only 1 receptacle neither 210.21(B)(3) or table 210.21(B)(3) apply.
Not likely the panel would point to a non-applicable table. I sorta remember the CMP said 'this is the way we want it'.
(The proposal was at least 10 years ago.)
I don't believe UL is sloppy. The general restriction, scattered through the code, is that derating to 80% is applied when the load is continuous (3 hr or more). As far as I know UL follows that. The NEC does not follow that in 210.21-B-2. Frying pans are not likely to be operated full power for over 3 hr unless you are using them in an aluminum foundry.
The NEC restriction is unenforceable. If YOU had a (noncontinuous) device with a 15A plug that ran at 13A would you be careful to only plug it into a 20A receptacle, or a 15A receceptacle that is the only one on the circuit (as required by the NEC)? No one else would. And the NEC can't prevent me from plugging in 6 - 1400W space heaters on a single 15A circuit. Oops that would be unsafe. I would put them on a
20A circuit.240.4-D (max 15A breaker for #14) is only relevant for 'modern' insulation. At least 2/3 of the wire in my house is TW or NM where 4-D is not relevant. And I believe a major basis for the 80% rule is that breakers (with a thermal trip) in an enclosed panel with other beakers can not be relied on to not trip if subjected to a continuous load. I am too lay to look it up, but I think the 80% rule does not apply if the breaker is rated for continuous, which electronic trip probably is.
Racking breakers (or motor starter units) is supposed to be one of the most dangerous operations. And dangerous on 480V.
I think it was at least 20 years ago OSHA discovered arc-flash and required worker protection. The NEC has added labeling in at least 2 sections. The labels give the energy that a worker can be exposed to in an 'event'. That guides what protection a worker needs. One (safe) racking operation had the electrician in an "arc-flash suit", with an electrician at the room door with a radio to another electrician at the source breaker to turn it off. (If there was an event that would probably be too late.) A lower levels of exposure 'natural fiber' clothes are worn instead of synthetic. Cotton may burn but it doesn't melt onto your skin like polyester. The smartest electrician I have met was very seriously injured in an arc-flash event. He was only trying to measure motor current with a clamp-on ammeter in a motor control center.
I am curious what the answer was in the ROP.
That is just the way Knox from U/L explained it to us.
I looked at the 2010 (for the 11 code) and I didn't see it. I will look at some others
I have an electric smoker with no thermostat that has a 1600w element and a molded 5-15 plug on it. It will trip a 15a breaker, yet it is stamped U/L.
It was only after the 17 code that 14ga TW was not rated at 20a in
310-15 table. (60c column). I still haven't seen what prompted that change. That used to be a regular test question. (a 16a FLA motor on a 40a inverse time breaker using 14ga wire). Mike Holt even referenced that in a recent EC&M article.
NFPA is digging this hole deeper. Look at the draft of the 23 I posted the link in another note.
On 10/8/2021 2:51 PM, snipped-for-privacy@aol.com wrote:
[combining 2 posts] [and I saw your 2 recent posts - haven't looked at links yet]I have looked at ROP/ROC on occasion because you can sometimes see what the logic was. Expect that is why "curious". (I did not discover either of these anomalies.) (I have seen at least one proposal from you.)
Your objection (20A on 15A ckt) is certainly not surprising. Have I mentioned that it is a stupid idea?
============================== >>
Damn. You made me look for my notes. I finally found them.
==================================== For 20A single on 15A ckt: ================================== For the 2008 NEC there was a proposal to change 210.12-B-1 (single receptacle) to require the receptacle be equal to the branch circuit rating. The argument was specifically about a 20A singe receptacle on a
15A circuit.The code panel rejected the change. Their statement [with my comments] was: "The recommendation would be overly restrictive in the case of some larger receptacle applications that do not directly correspond to the standard ratings of overcurrent protective devices." [It is not difficult to allow this and limit a 20A receptacle on a 15A circuit.] "The panel notes that a 20-ampere receptacle installed on a 15-ampere branch circuit is protected within it?s rating." [The panel apparently does not care that you can plug in readily available devices that are over the circuit rating.]
So the code panel apparently has no problem with a 20A single receptacle on a 15A circuit. But IMHO this can be tagged under 406.3-A, and it appears to me that the code panel for 406 does not agree. ============================
2008 NEC ROP----------------------
2-8 Log #822 NEC-P02 Final Action: Reject (210.21(B)(1)) Submitter: Jeffrey A. Fecteau, City of Peoria, Arizona Recommendation: Revise text to read as follows: Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than equal to that of the branch circuit. Substantiation: As currently written, it is currently being interpreted to allow a 20 ampere single receptacle to be installed on a 15 ampere individual branch circuit. 20 ampere single receptacle is not less than that of the branch circuit. This would allow a 20 ampere rated piece of equipment to be connected to a 15 ampere circuit. See supporting material for response to a question posed to Code Question of the day, hosted by NEIS, and answered by Ed Holt (Electrical Inspector - Architect of the Capitol - Instructor - The College of Southern Maryland) Note: Supporting material is available for review at NFPA Headquarters. Panel Meeting Action: Reject Panel Statement: The recommendation would be overly restrictive in the case of some larger receptacle applications that do not directly correspond to the standard ratings of overcurrent protective devices. The panel notes that a 20-ampere receptacle installed on a 15-ampere branch cirrcuit is protected within it?s rating. Number Eligible to Vote: 12 Ballot Results: Affirmative: 12 ================================= [I have not looked this up today] A while back I ran across 406.3-A which, IMHO, prohibits almost all 20A single receptacles on a 15A circuit: 15/20A receptacles "shall be installed only on circuits of the voltage class and current for which they are rated." This applies only to "grounding-type" receptacles, so you presumably could put an ungrounded 20A single receptacle as the only receptacle on a 15A circuit (and only in those cases where you can use an ungrounded receptacle). Oddness remains, but is greatly limited.(210.21 (B)(2) and (B)(3). of course allows a 15A receptacle on a 20A circuit.)
I would expect a rule for receptacles to be in the article on receptacles, 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.
The 20 amp outlet EXCEDES code requirement and ISA allowed by code on a 15 amp circuit (under certain conditiond)
Part 2
210.21-B-2 limits connected load to 80% (even for non-continuous for 2 or more receptacles on a circuit.==================================== From my notes:
=================================== There were proposals for 2002 (the oldest one I looked at), 2005, 2008 and 2011 to eliminate the table or make it apply only to continuous loads (as the 80% rule is applied elsewhere in the code). All were rejected.
The arguments that are often made to change table 210.21-B-2 to apply only to "continuous" loads are:
1 elsewhere in the NEC the derate to 80% is for "continuous loads" 2 it is a requirement that regulates what happens after the inspector leaves and is unenforceable 3 UL listed equipment (probably only non-continuous) is readily available that violates the rule.From the comments, it appears that at least one other code panel does not agree. This code panel seems to not play well with others.
The logic displayed seems to be we (NEC) are right they (UL) are wrong. [The other post the argument made at least minimal sense] ==============================
2011 ROP------------------- delete 210.21-B-2 rejected the ususal argument ======================
2008ROP attempts to delete table 210.21-B-2 - rejected ========================= 2005ROP-------------------------- attempt to get rid of table 210.21-B-2; rejected
*** PORTER: UL agrees with the panel action on this proposal, but not with the panel's statement. 210.23 permits an individual branch circuit to supply any load for which it is rated. For multioutlet branch circuits, use of noncontinuous appliances rated at 100 percent of the branch circuit does not result in a hazard. All branch circuit components, such as the receptacles, branch circuit wiring, and the overcurrent devices, when used for supplying noncontinuous loads, are evaluated for service at 100 percent of their full rating.--------------------------- negative on a similar proposal PORTER: Section 210.23 permits an individual branch circuit to supply any load for which it is rated. For multioutlet branch circuits, use of noncontinuous appliances rated at 100 percent of the branch circuit does not result in a hazard. All branch circuit components, such as the receptacles, branch circuit wiring, and the overcurrent devices, when used for supplying noncontinuous loads, are evaluated for service at 100 percent of their full rating. =================
2005ROC Comment *** Questions regarding how this requirement has been applied to products rated more than 12 amps and provided with 15 ampere plugs should be addressed to the responsible listing organization. [In other words, we (NEC) are right and UL is wrong] ====================== 2002 ROP-------------------------- change limits in 210.21-B-2 to continuous; rejected Substantiation: This change is necessary to provide consistency between this section and section 384-16(d), 210-20, 210-19 and other sections requiring the 80 percent rule. Portable appliances (such as microwave units and hair dryers) and relocatable power taps are UL tested for a maximum of 1800 watts on a 15 ampere branch circuit and operate as a non continuous load on these branch circuits without a problem. Panel 20 and Panel 2 have established a Study Task Group to bring some suggestions for a resolution of this issue. UL 498 tests receptacles at 150 percent of their rating so limiting the load on as now required by Table 210-21(b)(2) for noncontinuous load is unnecessary. See also Proposal 20-52 on page 668 of the 98 ROP. Statement by panel: Quote" the substantiation does not justify the reduction in rating to 12 amperes and 16 amperes for appliances rated between 12 and 15 amperes and between 16 and 20 amperes respectively." This Section as revised will make it mandatory for continuous loads only and not for noncontinuous loads. [??? not followed]
substantiation for a similar proposal:
*** A Task Group comprised of members from code-making panel #2 and #20 met on 7/14/99 at Underwriters Laboratories Inc. in Northbrook, IL and developed examples of the diversity of products that utilize 100 percent of the current rating of the plug. These included intermittent duty products such as microwaves, power tools, personal care products, exercise machines, kitchen appliances, and lawn and garden equipment. Evidence of problems stemming from excessive current do not exist with the above products. A review of manufacturers' complaint databases and the U.S. Consumer Product Safety Commission (CPSC) data shows no evidence of problems with cords on these appliances from excessive current draw. =========================== 2010 [ROP?ROC] in favor: The rule is necessary to correlate with the product standards for receptacles. 15A duplex receptacles are evaluated to supply 15A through the individual receptacle contact points. ========================== 2008 [ROP?ROC] The panel continues to maintain that the cord and plug connected load must not exceed the maximum load specified in Table 210.21(B)(2). =========================== 2005 [ROP?ROC] In the past, the panel has made it clear that cord-and-plug-connected devices are expected to be limited to 12 A if supplied by a 15 A attachment plug.
As usual you are full of it - bet yours eyes are brown --- LOOK at a receptacle - Up close - Leviton - Made in the USA so your Canuk Bashing id just that - They say VERY CLEARLY 15 amp 125 volt. on brand new ones anr 35 or 40 volt ones I have floating around.
The 20 amp I installed for the hangar door lift said 20 amps and 125 volts. The "power port" for the RV says 30 amps 125 volts, and the genereator plugs here at the house all say 250 volt 50 amp
The National Electrical Code, in article 210.21 (B) 1, 2, and 3, describes the requirements of single and multiple receptacles on a circuit.
The use of multiple 15 amp receptacles on a 20 amp circuit is permitted. A duplex receptacle is considered as multiple receptacles and is therefore permissible to use as the single, or one of several, multiple type receptacles on the circuit.
Part of the UL listing for the 15 amp receptacles is that they are capable of feeding through the 20 amp circuit, the primary difference between 15 and 20 amp receptacles being the faceplate configuration.
That said I DID check code and a 20 amp outlet is not specifically allowed on a 15 amp circuit - doesn't make any sense when a 50 is allowed on a 40 amp circuit - - - but when did code make any sense - you can have 6 duoplex 15 amp "outlets" on a 15 amp circuit and overload it with 3 6 amp devices - - -
And even worse it allows overlasding of the appliance cord if it isn't rated for more than 15 amps - and someone replaced the cord with one that is rated for less than 15 amps - AND the device draws more than 15 amps (a lot of IFs)
SO - code says no - but one 20 amp outlet (particularly a Simplex like we have on the hangar door) on a 15 amp circuit is actually a LOT safer than even a single Duplex 15 amp outlet - much less 6 - on a 15 amp circuit - and by the code, you are allowed to haveup to 12 outlets and lights @ 15 amps, but as the code states, fridges freezers, microwaves etc. must each be on a separate circuit but usually draw far less than 15 amps in total. ... Because if they throw a breaker your first indication is your food is rotten.
Think I said before - sounds like an interesting place to work.
You've probably heard it all. Many ways to get an arc, which is plasma - ionized air. With high available current the arc can continue until cleared by a fuse/breaker. A worker can get serious (like fatal) burns from radiated heat. There can be a blast from rapidly expanding heated air. Vaporized metal. Shrapnel from heat and magnetic effects. Any of it can permanently ruin your day. Also flash (eyes) and sound. The energy available at some locations prevents working on the equipment live.
The guy I know that got caught was doing something absolutely routine - amp-clamp a wire in a 480V motor control center. It is not known what happened but there was an arc-flash. He got serious burns, some from vaporized copper condensing on his skin (which was also poisonous). Was in the hospital quite a while with several plastic surgeries. The industrial plant bought power at distribution voltage level and owned the transformer from maybe 13.8kV to 480. Not only did one of the primary fuses blow, it damaged the fuseholder (should never have happened).
The other event I heard about was a field rep for a major manufacturer. Facility had a motor control center with an unused empty cubicle. He was measuring the space for what would fit. With a steel tape. He wound up on the floor on the other side of the room.
There was a reason OSHA increased regulation. I think they increased protection from shock at the same time (probably the hook and mat).
I have been looking at this stuff for almost 30 years. I got my IAEI
2A, 2B and 2C in 93. At a certain point I agree with the guys who say unenforceable rules about what some person might plug in are stupid. Maybe that is why 210.21 (B)(3) table was good enough. If I had a sea lawyer on a job quibbling about this, it's going to be a long day. It never really happened tho. I just want to be sure the conductors on the line side, in the walls are protected against the dumbest thing that can happen on the load side of that wall. Then we start looking at grounding/bonding, GF/AF protection and the other stuff.BTW did you see the 10a circuit thing?
210.23(A) Those used to just be alarm circuits but now they let you serve lighting outlets, fart fans and igniters ... not smokes ;) I didn't see if this needs AFCI.I just found this.
Why is it safer? Both receptacles will handle the rated 15A of the circuit. Both can be overloaded. But the 20A receptacle on a 15A circuit encourages people to think that it's a 20A circuit and to plug loads higher than 15A into it. Yes, it's protected by a breaker, but it's not safer. And since few are going to go to the panel to check the breaker, it misleads people into at the very least, creating overloads and breaker trips. If I have an appliance with a 20A plug and I see a 20A receptacle, I'm going to assume it's 20A, not 15.
Perhaps. But in reality, how many people would be able to identify a 20A capable receptacle by sight - and how many 20A 120v appliances are out there?
My rack-mount (2.2kva) UPS came with a NEMA 5-20 plug. It never has a load sufficent to draw anywhere near that amount of current (aside from the initial inrush), so why shouldn't I be able to plug it into a single 20A receptacle on a 15A circuit?
The more I read about this the more I believe NFPA doesn't believe there is a NEMA standard for plugs and receptacles. They just care that the current carrying capacity, marked on the device, is equal to or greater than circuit ampacity. It looks like the style only has to remain consistent in the "same premises"
"406.4(F)Noninterchangeable Types. Receptacles connected to circuits that have different voltages, frequencies, or types of current (ac or dc) on the same premises shall be of such design that the attachment plugs used on these circuits are not inter-changeable."
Beyond that we are just getting into a 110.3 area. You still need to use equipment according to how it is listed and labeled. I am really surprised nobody has pointed this out more often in the thousands of hours I have spent in classes, seminars, meetings and internet chats.
I think this is why they take a glancing blow at utilization equipment with unenforceable things like 210.21(B)(2)
I did see something else in the pipe for 2023, assuming it makes it through the comment period. AFCIs are moving from a bunch of specified circuits and locations to "do it". Most of the language in 201.12 is taken out and replaced with "shall be provided" so that means your oven, AC and water heater will need to be Arc Fault too. After all the problems they are having with HVAC on GFCIs in the 20, they may rethink that tho. There is a TIA suspending that GFCI requirement.
NFPA has a horrible habit of believing the crap the manufacturer reps on the CMPs say and demanding products be used before they are ready for the public. AFCI is an excellent example.
You poor thing - were your feelings hurt?
"210.6 - Branch circuit voltage limitations" - uses 120V nominal "220.5-A - says for calculations use 120V I said "The NEC uses "120V" and "240V"."
I am glad you agree with what I have written.
The point is it is not specifically prohibited, and thus is allowed. And the code panel has said that is what they intended.
What is the relevance of a 15A plug in a 20A device? Not allowed by NEC. Not allowed by UL. Is it allowed in Canada?
And your cord replacement is trivial. What if someone replaces the plug with a 50A one.
You missed the argument - code says yes.
In as much as a 15A duplex receptacle is rated for 20A total from both halves and is rated 20A wire-through, and is tested at 150% (=22.5A) I don't see any reason a 20A receptacle is "a LOT safer".
Cite (using NEC, not Canada)
Cite (using NEC, not Canada)
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