Is it a NEC requirement that any motor rated over 1/3 horsepower must be on a dedicated circuit?
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If that were the case my shop would need a breaker panel that measures 4' X 6'. ;-)
Work Safe, Count to 10 when your done for the day !!
Bruce S.
The basic requirement is that branch circuit conductors supplying a single motor shall have an ampacity not less than 125% of the motor full-load current rating.
I don't know the if's and but's applying to that, but following that general rule is likely to keep you out of trouble.
Basically, I have two tools wired 240V that have 1/2 hp motors. I want to put in two receptacles, but on the same circuit. I've read that 240 outlets can't be daisy-chained, so I'll put in a junction box. But then I read somewhere that motors over 1/3 hp had to have separate breakers. That seems like overkill since the amperage requirement on a 1/2 hp motor wired 240 is less than 2 amps. Even if you have two 1/2 hp motors and multiply by 200% for startup (induction motors), it's still WAY less than 20 amps (the size of breaker I plan on using).
"I've read that 240 outlets can't be daisy-chained, so I'll put in a junction box."You won't need a separate junction box, just pigtail the first outlet.
BruceT
When you hang out in the wrong circles, you are bound to get bad electrical advise. There is nothing wrong with having multiple outlets on a 240 volt circuit. The term "Daisychain" implies that the outlet is being used as a splicing device, and this should always be avoided because it is a primary source of overheating and fire. However, I don't believe this is the way you were referring to "Daisychain".
No, the NEC does not specify that motors of this small size need to be on dedicated circuits. If it did, then you could not purchase a hand-held router or a contractor's tablesaw with a standard NEMA 5-15 plug. It is unfortunate that there are people out there that read the code well enough to misinform you like this, but don't understand the basis behind the code enough to properly apply it. Code is there for a reason, and when these people can't tell you what the reason is behind the code, then it is a sure sign that they do not fully understand the NEC.(Oh, and a P.S.: The 125% rating is one of the most frequent misapplications of the code on the internet. The people that state this are generally just repeating what someone else told them without regard to the application or source. They repeat this because it makes them sound knowledgeable.)
Edited 8/24/2007 3:00 am ET by RickChristopherson
I'm curious about what misapplications of the 125% rule are the one to which you refer. The most common situations in the residential circumstances which most of the questions on fora such as this apply are clearly stated in that part of the electrical code extracted into the International Residential Code, 2003. Surely that means that the exceptions and caveats are the "fine print." While NFPA 70, the NEC, may provide alternatives and amplifications, following the basics in the IRC shouldn't create problems. That's why the prescriptive rules in the basic codes are used in the first place.
"On 15 or 20 amp branch circuits....The rating of any one cord- and plug-connected utilization equipment shall not excess 80% of the branch-circuit ampere rating." (E3602.3)
Similarly, while "A 30-ampere branch shall be permitted to supply fixed utilization equipment." the same paragraph continues on to say "a rating of any one cord- and plug-connected utilization equipment shall not exceed 80 percent of the branch-circuit ampere rating." (E2602.4)
Those don't really apply to the original posters question which turned out to be about multiple outlets on a 240 volt circuit. None of the cited paragraphs would rule that out.
However, E3601.5 speaks directly of branch circuits serving multiple loads or outlets. While the paragraph speaks about limits on fixed in place equipment on the same circuit with devices not fixed in place, its concluding sentence is "Multioutlet branch circuits serving lighting or receptacles shall be limited to a maximum branch-circuit rating of 20 amperes." italics added
RickChristopherson ---I agree with you completely.---SteveSchoene ---Your error is that you are using a design standard (NEC) as a use standard (plugging a tool into an outlet).
I still don't understand the distinction you make. Neither do the authors of the IRC, apparently.
They say that the rating of any cord and plug connected equipment that shall not be permitted to exceed 80% of the branch circuit ampere rating. That language surely specifies a standard for the use of equipment not the design of the circuit.
The design language is more like E3602.5 where the "the circuit conductors supplying a single motor shall have an ampacity not less than 125% of the motor full-load current rating." That's design standard language.
The distinction is reinforced by the math terminology used by the authors. While 80% of the circuit rating (as has been installed) is described for the equipment, the circuit rating to be installed (design) is based on 125% of the equipment rating. Of course, mathematically these rules give identical pairs of circuit and equipment ratings.
The IRC simply copies sections of the NEC. There is no thought on their part.
The IRC is a stand alone code, that draws from the NEC with its electrical sections which are produced by the National Fire Protection Association. While other methods of wiring covered in the NFPA are allowed, the IRC does not need to refer to NFPA 70 to provide standards within the relevant scope of the IRC since the IRC documentation is consistent with NFPA 70, just not exhaustive. The principal purpose of the codes is to provide standards that do not require engineers to design building systems in many situations. (That's not to say that engineering isn't allowed, and in some cases required.) It doesn't make sense to say the ICC just copied NEC without thought. The thought is in determining which sections are the relevant ones for single family residential construction.
Besides, if the quotes sections from the IRC are just direct verbatim copies from the NEC then it is the NEC itself that is making some standards for use, and some for design.
By the way, I'm not saying that there is any thing inappropriate with those rules, nor suggesting that their aren't circumstances where more complex considerations could come into play. Those would fall outside of the basic parameters involved in single family homes and basic shop wiring. Commercial and industrial uses are outside the relevance of the IRC and 99.9% of the issues brought to fora such as this. But except in the rara avis the basic rules 125% and 80% are the rules that do apply and their isn't much point in quibbling that in some other unusual situation more complex rules should be used.
Edited 8/24/2007 10:14 pm ET by SteveSchoene
Edited 8/24/2007 10:17 pm ET by SteveSchoene
Steve, I wasn’t directing my original posting specifically at you, it was directed at the multitude of people that keep repeating this information without a proper understanding of the National Electric Code. However, in hindsight, I do see that you fall into that category. Simply being able to extract quotations from code does not automatically mean there is an understanding of the code or the rationale behind the reasons for its statements.As I said earlier, the multitude of people that are repeating this information are doing so because they heard it elsewhere or for whatever other reason do not fully grasp the contents of the NEC. I am assuming you didn’t read the contents of the hyperlink above because you felt you knew enough already. Had you read that, it would have clarified this issue for you.
Because you did not read carefully enough to notice that this is applicable for continuous loads. The tools in a workshop are not continuous loads, nor do they operate at their full rating the majority of the time.
Reading this carefully, you will see that the circuit protection needs to be equal to 100% of the maximum non-continuous load, plus 125% of the continuous load.
You seem to think these are engineering documents, while they are in fact legal documents--ordinances mostly, and they are not published for the sake of electrical engineers. The language is clear. Under the IRC, which is the relevant ordinance in many jurisdictions, the limit is based on the equipment rated load, for cord and plug equipment. NEC 210-20 is not referenced (There is a cross-index appendix in the IRC.) The IRC does not rule out using the less conservative rule that you dig up, assuming that it is, as you suggest it is, properly applied to plug- and cord-connected equipment on 15, 20 and 30 amp circuits, if need be.
Still, it makes a lot of sense, just as the IRC drafters seem to think it makes a lot of sense, to make the general rule the 125% rule, leaving the finer distinction of continuous vs non-continuous to the "fine print" in other non-referenced sections of the NEC. I still think that is the better general advice, especially without being told explicitly that the loads being referenced aren't going to draw maximum current for 3 hours straight. That is very application specific.
In the real world, I'd bet a fair chunk, based on conversations recently held, that if I asked my electrician, currently set to wire my new shop, (i.e. garage), to install a dedicated circuit for a plug connected table saw with 17 amp cont. load rating on a 12 gauge, 20 amp circuit, he would decline. In fact, my table saw has a 15.5 amp rated motor, and his strong recommendation was to wire with 10 gauge, even though 15.5 amps of my current saw would certainly fall within the 80% rule, and a 20 ampacity circuit would follow the 125% rule. In my mind, his is a better, more useful recommendation than the one that says--ah--here is a rule that lets you skate closer to the edge. I would hire him over the guy who would take what amounts to a short cut, albeit legal, and likely, but not quite as likely, to be entirely safe.
These are not ordinances, and they are not the law, and they most certainly are published for the sake of electrical engineers (and electricians). And as I previously suspected, you have confirmed that you are not an electrician, but just someone that likes to read. If you understood what you were reading, then you would have already known that 12 and 14 gauge wire was already derated prior to the 15 and 20 amp breaker limits, so you are not “skating near the edge.†Moreover, as I alluded to in my original posting, you, like many others that mistakenly repeat this information, have not understood the purpose of the 80% derating. It is not a safety issue as you have surmised. That safety is built in elsewhere.You are free to wire your house however you see fit, but when you are presenting advice for others, with the aura of being knowledgeable, then you need to get your facts straight. This is the reason why electrical misinformation is rampant on woodworking forums, because people like you repeat misinformation as though it was fact. While the IRC may be written in a language that is easier for you to understand, it is not nationally recognized. The NEC is still the prevailing code for most jurisdictions across the country, and it will remain that way because the NEC does go into the details and language that is necessary for both engineers and electricians.
I am reading this post, as it is of some interest. I have but one question for you Rick. Are you a licensed electrician?
It's curious that you think these IRC or NEC are not ordinances and do not have the force of law. That's just plain not true in a great many jurisdictions. Open up a copy of IRC 2003, and turn to page v for a draft of the proposed ordinance. Go to web pages for your state and local jurisdictions and see exactly how they have been adopted, and in some cases modified by legislators.
As far as the issue of presenting advice, in contexts where all the possibly relevant detail is not at all likely to be known, the first rule should be that of conservatism. Adding the information that you can in some circumstances, if your assertions happen to be correct, feed a slightly more powerful motor with a circuit than the basic rule of thumb would allow is not good advice. I spent a lot of time in academia and know quite well what an academic argument is. I don't know if you are correct or not, but I do know, and have never asserted more, that following the basic 125%/80% rules isn't going to lead people astray.
No, the NEC and IRC are not ordinances or laws of any type. The law is the local ordinance that adopts the NEC as a local requirement. The NEC is not automatically binding unless, and until, a local jurisdiction makes it binding, and even then, the local law includes provisions for how the code is applied and interpreted. These documents were not created by lawmakers, they were created by a consortium of engineers and electricians.
It isn’t a matter of being conservative or not; it’s a matter of understanding code. You wrote, “...I do know, and have never asserted more, that following the basic 125%/80% rules isn't going to lead people astray.” Contrary to this assertion, you are in fact leading people astray. You are telling people that code dictates something that it does not. This by definition, is leading people astray.
Putting a 1-1/2 hp tablesaw on a 20-amp circuit is begin conservative; telling people that they must use a 20-amp circuit is leading them astray. This is something that the proponents of this discussion overlook: If a cord-and-plug connected device cannot exceed 80% of a circuit’s ampacity, then how can you buy a 1-1/2 hp tablesaw, that is UL listed, with a NEMA 5-15 plug installed on the cord? If the 80% assertion was correct, then all of these tools would have a mandatory NEMA 5-20 plug on them to prevent someone from connecting them to a 15-amp circuit. Part of the UL certification process is to ensure that the product conforms to the National Electric Code, so if the code did state this, then UL would not permit the 15-amp plug on a product that draws 15 amps (or anything over 12-amps, for that matter).
The other thing that the proponents of this topic misunderstand is the purpose of the statements in the NEC. This particular circuit derating is not put there as a safety concern, but as a convenience issue for the consumer/property owner. 12 gauge wire is actually rated to handle 25 amps of current, but you are not permitted to install 12 gauge wire on a circuit larger than 20 amps. As I said earlier, safety margins are built in elsewhere in the code; this particular derating information is not part of that safety margin.
When adopted and incorporated by ordinance those provisions become law no matter who did the original drafting. This arguments seems to be a retreat to tilting at a purely symantic windmill.
Perfection is the enemy of the good. Going "astray" has real consequences in one direction (overheated wiring), and trivial ones (a few dollars for a larger gauge wire) in the other.
Your UL example is not apropos since it derives from UL consideration of a specific piece of equipment whose usage is explicitly known. The generalized "motor" applications often the basis of questions do not provide that information and can't be known for sure to be continuous or non-continuous loads. In the face of uncertainty, always assume the worst. This seems to be ignored in favor of pendantic "correctness", an error not made by the drafters of the IRC who leave that fine point to those seeking a slightly cheaper job.
There is nothing in any of these codes or proposed codes that is not at it's root based on safety. If "convenience" is the issue it is directed at making it easier for the consumer/property owner do the safe thing.
This is an interesting discussion between you and Rick. You both have the Taunton posters' good health at heart.And it is nice to see that you both refrain from personal abuse while discussing the various minutae of the subject.Some other posters (and I am only thinking of 2 or 3 here) would do well to follow your example.My $0.02 Cheers,Peter
There are many aspects of the NEC that are not purely rooted in safety. While it is true that a majority of the NEC is rooted in safety, another aspect of the NEC is to protect the interests of the end-user. Do you think that permitting 15-amp receptacles on 20-amp circuits is rooted in safety? No, it is rooted in cost and convenience. A NEMA 5-20 receptacle accepts the use of a NEMA 5-15 plug, so is there any reason why code should permit an electrician from using a lower ampacity device on a higher ampacity circuit, outside of the fact that NEMA 5-15 receptacles are more common and more cost effective? (As TV’s Magnum PI would say, “I know what you’re thinking...” so before you answer that, consider that the same rationale does not apply to 30-amp circuits. You are not permitted to install a 20-amp receptacle on a 30-amp circuit. The only other circuit where this again becomes applicable is when you can install a 40-amp receptacle on a 50-amp circuit.)
Why is the UL example not appropriate? This actually goes to the root of the discussion, so it is absolutely appropriate. Either the load is continuous or it is not. If the load is continuous, then the circuit needs to be derated. If the load is not continuous, then the rule does not apply. The proponents of this discussion are overlooking this aspect of the code when they continually recite the derating requirements, and if I’m not mistaken, you did this too. By saying, “...consideration of a specific piece of equipment whose usage is explicitly known,” you acknowledge that there is a distinction between continuous and non-continuous loads, yet you are claiming that code does not permit this distinction. If the distinction is not permitted, then it doesn’t matter who has made the distinction, because it is not permitted to be made. In reality, the distinction does exist, and it must be applied.
Let’s take an example, and I will use the 30-amp circuit to avoid ambiguity permitted with other circuits. If an electrician installs a 30-amp circuit, then he Must install a 30-amp receptacle. He is not permitted to install a “derated” receptacle to account for continuous loads. It cannot be larger, and it cannot be smaller. How that circuit gets used is no longer up to the electrician once he leaves the jobsite. If the end-user plugs in a device that runs 24/7, then that circuit must sustain that load without overheating or without damage, even though the NEC classifies this as a continuous load. The NEC specifically states that the circuit must support whatever load is connected to the circuit, insomuch as it does not exceed the capacity of the over current device.
If this aspect was not true, then the NEC would have dictated that only 80% rated receptacles could be installed on any circuit, because this would prevent any single device from exceeding 80% of the circuit’s capacity. Given this rationale, a 30-amp circuit could only have 24-amp receptacles installed, which is specifically prohibited. You said, “ In the face of uncertainty, always assume the worst.” Well that is exactly what the NEC has already done. The ampacity rating of a circuit has already taken into account the worst case situations, and provisions have been made to prevent overheating a circuit.
I can't remember when a post with material WAY over my head kept me interested! You guys are awesome.
Anyway - my 2 cents worth - the IRC (not sure about the NEC) can basically be considered a "minimum code". Meaning you can still over-design if you or the jurisdiction having authority sees fit. i.e. cast iron soil pipe instead of PVC, copper supply tubing instead of plastic, sprinklers instead of no sprinklers, brick instead of vinyl siding... you get the idea.
Evening Steve,
It's all about the heat generated by electrical useage, heat is the byproduct of electrical action, which is why the electrical code is written inpart by those concerned with fire prevention as well as those concerned for personel safety.
I've got chicken cookin on the grill right now, so if you'll click on this link,
http://ecmweb.com/mag/electric_sizing_circuit_breaker/
you and everyone else can get a very clear understanding of what's involved with sizing breakers and why. You will also understand more clearly the relationship of 80% and125%.
Gotta flip the chicken,
Chris, a grillin fool.
Andy,
While I admit that I held the same sentiments as you when this discussion started, I am grateful that Steve has engaged in this discussion. I believe that the last several postings have provided a great vehicle for educating the other readers on this forum without some of the hotheaded debates that would typically sidetrack such a discussion.
Of all the woodworking forums that I frequent, this forum is the only one where electrical misinformation is still running rampant without any proper checks and balances. Even though it is easy to tell people, “no, that’s not correct....” about their previously held misconceptions, that information is quickly lost on the masses, or in the din of the other voices repeating the same misinformation.
My hope is that with the number of people that are obviously reading this thread, that some of this information begins to sink in, and the frequency and fervor of the misinformation diminishes to a more manageable level.
So quite to the contrary, if there are any remaining doubts, questions, or disbeliefs still floating out there, I would just as soon address them now before they continue to fester, only to be repeated again later.
First, I don't claim any authority--and haven't right from the first--read my very first post in this thread. But the only matter of any substance to me is that the "experts" are so intent on expertness that a more conservative rule of thumb is discarded in favor of a complex set of arcania which if mis-applied are more likely to use up the various safety margins built into the code standards.
Perhaps in an ideal world only licenced electricians would ever add a circuit in a home shop, but that's not realistic to assume, and isn't going to happen just because experts focus on the complexities.
There is absolutely nothing wrong in explaining the complexities more clearly as Rick has been doing. However, I don't think that leads to better advise.
The full complexity is quite proper to apply if one is on the scene and in full possession of the facts of the situation. But if that isn't the case, as it never is on fora such as this, it isn't such a good idea to bring out the less conservative and more complex solutions that are more easily misunderstood. The basic rule of thumb is simple, easy to understand and to apply, and even though it may not lead to the ideal result in all cases, does lead to safe results.
But it is still also interesting that the well-respected licenced electrician whose firm will shortly be working on wiring my shop is quite firm in following the rule of thumb and would not put in a 20 amp circuit for a 17 amp rated table saw in a hobbyist shop. In fact, he would prefer to overwire several circuits where equipment might be upgraded in the future. I suspect that's the way lots of practicing electricians, whose assets are ultimately on the line, weigh in on the issue.
Andy, you’re right and I take my previous posting back. I thought I had been making some progress here, but I guess not.
Steve,
All you are doing now is just backpedaling. You started out this discussion because you were telling people that it was required for them to derate their circuits. When I told you that it was not a code requirement, you adamantly denied that. Now that it appears that I have finally convinced you that it is not a code requirement, you are still stating that it is something that people should blindly do, just to be extra safe.
Well if it’s not a code requirement, then who are you to be suggesting to other people that they should be doing it? You are not an electrician, you are not a code authority, yet you are advising people to do something that is not required in the code. It is one thing for you to decide to do something in your own home, but it is an entirely different matter for you to be telling people that they must also do what you think is best when it is not supported by code and you do not have the proper background to be providing that advice.
"...a more conservative rule of thumb is discarded in favor of a complex set of arcania which if mis-applied are more likely to use up the various safety margins built into the code standards." I don’t know where you are getting this from. First off, who’s rule of thumb is it, yours? There is nothing complex about it. Either the motor is fully loaded continuously or it is not. A or B, True or False, it is not that complex. You are trying to make it seem complex because that suits your needs for justifying your position.
So if you are just trying to be conservative, where does it end? How do you, a person not familiar with electrical issues, decide how far this conservativeness should be taken? Should I wire my house exclusively with 30 amp circuits because I would know without forethought that they would never be fully loaded? Someone with a proper electrical background could answer that question, but you are not that person. So if you cannot say how far this should be taken, then how can you consider yourself qualified to state that it should be applied at all?
By the way, while academia is a word, arcania is not. Even though I would assume you meant arcane, that is only applicable in your world. While you might think that understanding this rule is arcane (i.e. mysterious, secret, obscure) that is only because it is something that you are not familiar with. That does not mean it is not familiar to those that properly understand the NEC. As I said early on, you spend too much time trying to make yourself sound knowledgeable. I first noticed this in your second posting (and now again in your forth) where you italicized "Fora" in an effort to point out to others that you were using what you think is the proper plural for "forum." Once again, you did not do enough research, or you would have known that the more common "forums" is in fact a proper plural of "forum." It is your "Fora" that is "arcane."
And another by the way, your "respected" electrician is respected by "you" because he gave you the answer you wanted to hear. Being respected by people that don’t know any better is not the same as being respected by people that do. If this is the level of his understanding of NEC, then I can assure you he would not be respected by his peers. As I stated back when this discussion started, the people that are repeating this misinformation are those that are not properly versed with the NEC.
Oops, arcana is the correct plural noun of arcanum, as data is of datum, and fora is of forum. Forums is also correct. Fora is italicized following the basic rule calling for foreign words to be treated that way until or if more widely adopted into English.
I never said that the 125% rule was the ONLY code compliant rule, never. But it certainly is code compliant, not just minimally, code compliant. You have to reach past the IRC, which, where adopted, is fully sufficient code applicable to one- and two-family dwellings, into the additional standards of the NEC to get there. Fine, it's a nice display of knowledge, and can save a few dollars, but it isn't necessary.
I don't have to have the personal knowledge of the entire NEC to properly conclude that the 125% rule is OK to follow. The International Code Council (ICC) has told us that when it published the IRC. It's the IRC's "rule of thumb." It's natural for experts to defend their turf, but one of the reasons for published codes is to make it possible to build safe buildings without having to have an engineer design every wall, roof or circuit. There is a cost, but using a slightly larger wire is just exactly the same as using 16" spacing for 2x4 studs when there are circumstances where 24" would work.
Continuous is completely obvious? But how long at maximum current--it's not really 24/7 is it?
I won't comment on the ability to judge a licensed master electrician's knowledge of the NEC based on his preferences for wiring a shop circuit.
Steve,
It is not my intention to throw any stones here, I'm trying to figure out where the confusion may lie.
Based on one of your previous posts (#14 in this series), you mentioned ordinances pertaining to enforcement (in your area, I assume). Also taking into account what your electrician proposes to do in your shop. I am wondering if you live in an area where strict building codes are adhered to. Meaning, some places simply follow standard Uniform Building Codes, BOCA, and NEC. Some areas follow a more stringent code enforcement requiring guidlines that are over and above what is mandated by the above said codes.
Chris.
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