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Old 10-10-2015, 03:28 PM   #16
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Originally Posted by InPhase277 View Post
Look who posted it. Are you surprised?

No. But Id rather the OP get a correct answer. It doesn't matter anyways since we are all on block. In two weeks we'll see this same answer in a new thread.
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Old 10-10-2015, 04:01 PM   #17
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Originally Posted by Jump-start View Post
Not true, there is also a thermal component:


http://goodsonengineering.com/wp-con...rMyths_web.pdf


The magnetic component usually starts around 10x the breaker's handle rating and that is intended for short circuits. Overloads like a 30 amp load on a 15 amp breaker are via bi-metallic strip.
All accurate, and it goes even further. For a long time there were breakers sold that didn't have a magnetic trip system at all. One way to know that Jump-start is right, without having to know breaker engineering, is to notice that overloads don't trip breakers immediately. Short circuits do, but overloaded circuits can take minutes to trip. Why? Because the breaker has to warm up enough for the bimetal strip to move.
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Old 10-10-2015, 04:15 PM   #18
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Where is this "rule" you speak of? I would be interested in your research regarding such. Please post.
National Electrical Code, 210.20(A), at least that's the section number in the 2011 edition.
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Old 10-10-2015, 04:33 PM   #19
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National Electrical Code, 210.20(A), at least that's the section number in the 2011 edition.
Has nothing to do with some "80% rule". Thanks for trying.
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Old 10-10-2015, 04:59 PM   #20
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Originally Posted by NotaDIY/Pro View Post
Has nothing to do with some "80% rule". Thanks for trying.

The NEC defines what is a continuous and none continuous load. Where the load is continuous the circuit can only be loaded to 80% of the handle rating.


What do you have in mind?
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Old 10-10-2015, 05:16 PM   #21
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Correct , the general rule is 80% for continuous load . I always figured the requirement for an external Main had more to do with the wishes of the fire department than the electrical utility .

God bless
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Old 10-10-2015, 05:52 PM   #22
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Originally Posted by NotaDIY/Pro View Post
Has nothing to do with some "80% rule". Thanks for trying.
It says not less than the non-continuous load plus 125% of the continuous load. So, a continuous 16 amp load would require a 20 amp breaker (1.25 * 16 = 20). 16 amps is 80% of the breaker's nominal capacity (0.8 * 20 = 16). If the load were completely non-continuous then a 20 amp load could be served by a 20 amp breaker. In other words, breakers are derated to 80% when serving continuous loads. Are you looking for something else?
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Old 10-10-2015, 07:29 PM   #23
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Quote:
Originally Posted by NotaDIY/Pro View Post
Where is this "rule" you speak of? I would be interested in your research regarding such. Please post.
210.20(A) Continuous And Noncontinuous Loads. Where a branch circuit supplies continuous or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125% of the continuous load.

The inverse of 125% = 80%.

This is generally referred to as the '80% rule' because in a lot of instances a breaker cannot be loaded to more than 80% of its rating.

There are exceptions of course.........

P.S. Article 100 defines a continuous load as a load where the maximum current is expected to continue for more than 3 hours.

One notable exception is 422.13 Storage Type Water Heaters. A fixed storage-type water heater that has a capacity of 120 gallons or less shall be considered a continuous load.

The idea of breakers transferring their heat to adjacent breakers is somewhere in the UL White Papers and is the basis of the 80% rule.
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Old 10-10-2015, 08:08 PM   #24
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Well, I will concede. However, Mike Holt says otherwise. Just never heard of using the inverse of 125% to accomplish load calcs, perhaps there is something to it, I really don't know. Could be there is something to learn here, but not seeing it.
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Old 10-10-2015, 09:32 PM   #25
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Originally Posted by gregzoll View Post
The only place in above the 38th parallel north that you would see outdoor disconnects is RV & Mobile Home parks, or on Farm properties around dryers, grain elevator equipment, farm animal housing.
Might have to go back and tell my customers that their house is actually a RV or in a trailer park . Boy did the realtor get one over on them. Imagine 300 and 400K dollars for a trailer.
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Old 10-11-2015, 04:18 AM   #26
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Originally Posted by NotaDIY/Pro View Post
Well, I will concede. However, Mike Holt says otherwise. Just never heard of using the inverse of 125% to accomplish load calcs, perhaps there is something to it, I really don't know. Could be there is something to learn here, but not seeing it.
Just mathematics . Does not matter who said what .

16 amp continuous load x 125% = 20 amp Circuit Breaker

20 amp CB x 80% = 16 amp continuous load

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Old 10-11-2015, 09:23 AM   #27
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Might have to go back and tell my customers that their house is actually a RV or in a trailer park . Boy did the realtor get one over on them. Imagine 300 and 400K dollars for a trailer.
Another place you won't find outside disconnects is on ships. When Greg was in the Navy, he did electric work on boats and they never had disconnects in the middle of the ocean, therefore it can't happen anywhere else. Did you know Greg was in the Navy? If need be, he can ask an old Navy electrician on another forum to make sure. But at any rate, Navy. Navy trumps all. Just... Navy.
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Old 10-11-2015, 10:29 AM   #28
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Originally Posted by gregzoll View Post
The only place in above the 38th parallel north that you would see outdoor disconnects is RV & Mobile Home parks, or on Farm properties around dryers, grain elevator equipment, farm animal housing.
Don't forget about all the rooftop HVAC units out there for the malls and office buildings and restaurants. I guess you didn't remember those .


Around me almost all the roofs are outside. You did say ONLY didn't you? Wouldn't want to be accused of trolling.
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Last edited by Jim Port; 10-11-2015 at 10:36 AM.
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Old 10-11-2015, 11:06 AM   #29
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Originally Posted by InPhase277 View Post
Another place you won't find outside disconnects is on ships. When Greg was in the Navy, he did electric work on boats and they never had disconnects in the middle of the ocean, therefore it can't happen anywhere else. Did you know Greg was in the Navy? If need be, he can ask an old Navy electrician on another forum to make sure. But at any rate, Navy. Navy trumps all. Just... Navy.
He does have a lot of experience with floating neutrals though.
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