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Joined: Nov 2007
Posts: 763
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Sorry, I meant 75-degree C.
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Joined: Mar 2011
Posts: 98
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We are getting into an area about the difference between safe and legal. 240.4(D) was put there for safety and it is really there because the NFPA people know 14/12/10 is used on circuits where the loads are likely to be cord and plug connected.
The assumption is that the installer will not know what the user will actually plug in. People will keep plugging in things until the breaker trips and then unplug the clock. They build the 80% into the maximum breaker size. That still does not change the requirement that hard wired continuous loads are still limited to 80% of the breaker size, as KJay points out.
Whether the NFPA should put the same kind of exemptions for lighting loads into the code that they have for motors is conjecture but you still have a few weeks to write a proposal and see what they say. Agreed, but the use of 100% rated OCP is mostly limited to industrial and institutional settings where competent personnel are generally involved in the design, construction and maintenance of said facilities. That still does not change the requirement that hard wired continuous loads are still limited to 80% of the breaker size, as KJay points out.p What requirement is that? If the fixture, receptacle, piece of equipment, etc is rated for 20 amps (or whatever the 100% rated OCP is) then you are good. The code does not address derating end-use devices as far as I know.
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Joined: Jul 2004
Posts: 9,794 Likes: 15
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I suppose I could write 1000 words but here is a picture from the handbook. ![[Linked Image from gfretwell.com]](http://gfretwell.com/electrical/continuous%20load%20example.jpg)
Greg Fretwell
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Joined: Mar 2011
Posts: 98
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I suppose I could write 1000 words but here is a picture from the handbook. Greg, You failed to include the 100% assembly exception that immediately follows that example.....
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Joined: Jun 2004
Posts: 1,273
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100% assemblies don't exist.
Tesla
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Joined: Mar 2011
Posts: 98
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100% assemblies don't exist. If you mean panels and breakers, yes they do, but they have to be specified that way and there is a cost impact (sometimes significant). specified and used at the proper location and time though and it will save money otherwise spent on oversized branch and distribution gear feeders and breakers.
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Joined: Jul 2004
Posts: 9,794 Likes: 15
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I am having a hard time finding a breaker that says it is rated for 100% continuous load.
Greg Fretwell
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Joined: Mar 2011
Posts: 98
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I am having a hard time finding a breaker that says it is rated for 100% continuous load. Finding 100% rated breakers hasn't been the problem, but finding a 20 amp 100% rated breaker is proving difficult, which is annoying since I've seen them spec'd and installed on several waste water treatment plants over the last 5-6 years.
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Joined: Apr 2002
Posts: 7,335 Likes: 7
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Guys:
We are talking about what seems to be either a design issue that fell through the cracks in a commercial setting, not industrial, etc.
Vin: I see all your points, but they are out of the league (IMHO) on the OPs points.
John
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Joined: Oct 2002
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I sent a request in to the SQ.D company to see if they could tell me what the 20 amp QO breaker was actually rated at. Haven't got a response yet, but obviously whatever it is rated at, on the job in question, it has been holding for 2 years at 19 amps. Of course the 5 emergency ballast that are bad in the facility right now might bump it up a little more, when they are replaced ,( of course I realize the amperage, if any, will very minimal). I've sent my information in, to my customer, and am waiting on their reponse as to what they want me to do.
I've also sent "South Wire" (one of the manufacturers) an email to see if they could actually tell me what #12 thhn is good for, before the insulation actually breaks down in real life, in their test labortories. Still looking for their response also. Thanks again for all the response.
Last edited by sparkync; 11/04/11 03:49 PM.
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