Example D4(b)

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iwire

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I will agree that for dwelling units these terms probably do not apply. The NEC does a reasonable job at providing guidance for determining the minimum size service for resi- and commerical loads.

I don't use the NEC for the work I do, it is all engineered.

It seems in this case your design would be less the the normal NEC minimums. I am not at all saying what you engineer does not work perfectly, just that in this case the NEC would provide a larger service then the method described here.

Basically, think of demand as what is the actual running load. Motors are the easiest to think of. Say you have a 5 hp motor 208V 3ph motor, the rated FLC is 16.7A. But the pump connected to the motor will never draw more than 87% of the motor power, and therefore the running load is 0.87 x 5Hp. So, when running it will never draw more than 14.6A. That is the demand (running) load.
 

Hameedulla-Ekhlas

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No, the NEC also addresses non-dwelling units. It applies to hospitals and laboratories, factories, office buildings, retail outlets, and any other type of building you can name.

But I think, NEC has considered the diversity factor and I have seen an example in that. Let me to find that for you now or if you know please advise me.
 

charlie b

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But I think, NEC has considered the diversity factor and I have seen an example in that.
I just did a word search of the NEC, looking for the phrase "diversity factor." It showed up only one time, at the bottom of table 520.44. That was in the context of "load diversity," a phrase the NEC uses several times and never defines. So I conclude that the concept of "diversity factor," as I have defined that term earlier, does not appear in the NEC.

 

Hameedulla-Ekhlas

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AFG
I just did a word search of the NEC, looking for the phrase "diversity factor." It showed up only one time, at the bottom of table 520.44. That was in the context of "load diversity," a phrase the NEC uses several times and never defines. So I conclude that the concept of "diversity factor," as I have defined that term earlier, does not appear in the NEC.

I am agree with you and till yet I could not too. If I find anything, I will share it.
 

Hameedulla-Ekhlas

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Yes, bob: thank you for this post and I have seen many times this pdf file. So, I am insisting on, why NEC BOOK does not have such an example eventhough the diversity factor is one of the important engineering concepts. There is big difference between demand factor and diversity factor.
Economic and cost is one of the vital point of engineering.
 

charlie b

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. . . why NEC BOOK does not have such an example even though the diversity factor is one of the important engineering concepts.
Put simply, the NEC is not an engineering book. The NEC is all about safely installing an electrical system. It is not concerned with design principles at all.

 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Put simply, the NEC is not an engineering book. The NEC is all about safely installing an electrical system. It is not concerned with design principles at all.

NEC has already has, sizing the feeder, sizing the breaker, sizing the branch and consideration the factors in different condition, special equipment for safety, using formula, and etc... Are not they design ?
 

kingpb

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SE USA as far as you can go
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Engineer, Registered
It seems in this case your design would be less the the normal NEC minimums. I am not at all saying what you engineer does not work perfectly, just that in this case the NEC would provide a larger service then the method described here.

I suppose that would be the case, if that's all I had to go by was the deficient NEC, but then again I havn't seen too many 25,000 Hp motors installed on a 120/240V system.

I don't want to get chastized for getting off topic, but I see people that spend a lot of time trying to meet the minimum NEC requirements instead of doing a well thought out and practical design based on real knoweldge of equipment and good engineering practices. The NEC is not supposed to be a design book, but yet it seems that people just shoot for the minimum as if that is what they are supposed to do.
 

iwire

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Location
Massachusetts
I see people that spend a lot of time trying to meet the minimum NEC requirements instead of doing a well thought out and practical design based on real knoweldge of equipment and good engineering practices. The NEC is not supposed to be a design book, but yet it seems that people just shoot for the minimum as if that is what they are supposed to do.

It might be related to the fact that a large majority of the work goes to the low, or lowest bidder.
 
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