I need help with a complex calculation

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Smart $ said:
Well for that we're getting into interpretations, where opinions vary. First, 220.14(A) says outlet, not receptacle. Then it goes on to say for a specific appliance or other load not covered in 220.14(B) through (L)... and receptacle outlets ARE covered in (I) through (K).

I'm not saying you are incorrect... just my belief it's not generally viewed or calculated that way.
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I see your point as well. It does say outlet.
 
So, from what I have gathered from you guys. I need to recalculate 11 through 14 to 180va each, since they are receptacles. And multiply that by 1.25. Then the rest is cool? So, far? I can see, by the way I am going about this. I will have this down pretty good, with a real good understanding of it by the time I am all the way to the end of this calc. That's exactly what I am after. Anybody have any feedback on that book, I mentioned? I am thinking about ordering it. Unless, someone knows of a better resource?
 
They are receptacles. So just use 180va. like all receptacles, Then multiply by 1.25 for continous?
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Being the loads at 125% continuous are still less than 180VA, I'd just include the receptacles in the calculation for number of general purpose receptacles (i.e. at 180VA per, and not list as specific loads).


Huntxtrm said:
I understand what you are saying, I was just calculating for a 20 amp 120 volt circuit feeding them, as the true load is not known. And it is a dedicated circuit. Which, I am taking is wrong. I need to derate the 20 amp circuit for continuous loading? Is this what you are saying?
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It's not wrong if you don't know the true load... but a 20A circuit can only be loaded to 80% max' (reciprocal of 125%) before applying 125% for continuous... so the 20A includes the 125% continuous factoring.
 
I understand. That is the route I will take from now on. Is the rest good so far? If it is, I'll fix up my calculation thus far, and continue. And Thanks for helping me out. It is appreciated.
 
Smart $ said:
I completely understand some willingly accept the practice...
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Thanks for your interest in this matter. I read outlet as mentioned in (A) as any outlet, including rec outlet. I'm going to run this by a couple of my more knowledgable EI's here as presented from your perspective instead of mine.
 
chris kennedy said:
Thanks for your interest in this matter. I read outlet as mentioned in (A) as any outlet, including rec outlet. I'm going to run this by a couple of my more knowledgable EI's here as presented from your perspective instead of mine.
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I'm curious what their response will be.

Another point for your perspective is 220.14's general statement, "the minimum load for each outlet for general-use receptacles". It could be said these less-than-180VA loads are not using general-use receptacles. The NEC doesn't define a general-use receptacle.
 
Smart $ said:
I'm curious what their response will be.

Another point for your perspective is 220.14's general statement, "the minimum load for each outlet for general-use receptacles". It could be said these less-than-180VA loads are not using general-use receptacles. The NEC doesn't define a general-use receptacle.
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my inclination would be to use 180VA per receptacle and not worry about it. it won't change anything significant in your application.

I would use an 800A breaker. There is no difference in cost between a 600A and an 800A breaker in an 800A PB.
 
petersonra said:
my inclination would be to use 180VA per receptacle and not worry about it. it won't change anything significant in your application.

I would use an 800A breaker. There is no difference in cost between a 600A and an 800A breaker in an 800A PB.
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I agree with first part, and so noted in earlier post.

And while no difference in cost of breaker, opting for an 800A main breaker in a service PB would [likely] result in using larger SEC's, which would add to the cost.
 
Smart $ said:
I completely understand some willingly accept the practice...

But just to add a little more rationale to the matter, 220.14(L) regards outlets other than covered in (A) through (K)... which amounts to outlets with no load. Seems contradictory these are required to be calculated at 180VA per if an outlet with less than 180VA is allowed to be calculated at face value.
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Smart $ said:
I'm curious what their response will be.

Another point for your perspective is 220.14's general statement, "the minimum load for each outlet for general-use receptacles". It could be said these less-than-180VA loads are not using general-use receptacles. The NEC doesn't define a general-use receptacle.
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The second quote here kind of answers what I was going to bring up. Just what is a "general use receptacle"?

You may feel a receptacle with only 100 VA of intended load needs to be calculated at 180 VA, if so then the same logic says an intended 1200VA load in same type of receptacle should also be calculated at 180 VA.

IMO if we know what the load will be then we calculate based on the load, otherwise just use 180 for all recepacles that have no specific intended use.
 
Smart $ said:
I agree with first part, and so noted in earlier post.

And while no difference in cost of breaker, opting for an 800A main breaker in a service PB would [likely] result in using larger SEC's, which would add to the cost.
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Would that change the service conductors? I thought they were sized according to the load and not the downstream OCPD.
 
petersonra said:
Would that change the service conductors? I thought they were sized according to the load and not the downstream OCPD.
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"...protection shall be provided by an overcurrent device in series with each ungrounded service conductor that has a rating or setting not higher than the allowable ampacity of the conductor." [230.90]
 
kwired said:
You may feel a receptacle with only 100 VA of intended load needs to be calculated at 180 VA, if so then the same logic says an intended 1200VA load in same type of receptacle should also be calculated at 180 VA.
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That is not correct. 220.14(I) doesn't say that receptacle outlets shall be calculated at 180 VA, it says that they shall be calculated at not less than 180 VA.
 
Huntxtrm said:

Motor Loads:

1. 10 hp pump 460v x 14.2A x 1.732 = 11,313 va non-continuous

2. 10 hp pump 460v x 11.5A x 1.732 = 9162 va non-continuous
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Per 220.14, and 220.5(A), your motor load calculations should be based on the nominal voltage of 480V (and as Smart$ pointed out, based on the FLA from the table in Art 430.)

See, for instance, Example D2(b) in the Annex, where the load for six 7A, 230V air conditioners is calculated as 6*7A*240V=10.08kVA.

Or, Example D3(a), where the load for a 7.5HP, 460A air compressor is calculated as 11A*480V*1.732=9150VA; and the load for a 1.5HP, 460V grinder is calculated as 3A*480V*1.732=2490VA

(Oddly, the example of air conditioning in D2(b) uses 230V, but that value is excluded because the heat is larger.)
 
david luchini said:
Per 220.14, and 220.5(A), your motor load calculations should be based on the nominal voltage of 480V...
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I know the Examples* support your statements, but I often wonder whether it is required. That is, 220.5(A) starts "Unless other voltages are specified..." and 460V is specified in Article 430 tables.
 
Smart $ said:
I know the Examples* support your statements, but I often wonder whether it is required. That is, 220.5(A) starts "Unless other voltages are specified..." and 460V is specified in Article 430 tables.
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That's why I used 460v. I know its not nominal, but that is the voltage in the table. Why, would the NEC use voltages, that are not nominal, in a Table Anyway? Is it because that is what is generaly listed on the motor name plate?
 
david luchini said:
Per 220.14, and 220.5(A), your motor load calculations should be based on the nominal voltage of 480V (and as Smart$ pointed out, based on the FLA from the table in Art 430.)

See, for instance, Example D2(b) in the Annex, where the load for six 7A, 230V air conditioners is calculated as 6*7A*240V=10.08kVA.

Or, Example D3(a), where the load for a 7.5HP, 460A air compressor is calculated as 11A*480V*1.732=9150VA; and the load for a 1.5HP, 460V grinder is calculated as 3A*480V*1.732=2490VA

(Oddly, the example of air conditioning in D2(b) uses 230V, but that value is excluded because the heat is larger.)
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So, for safety sake. To make sure my service is not undersized. I should use 480V nomatter what is tabled or nameplated? The seems to be a grey area, to me, at this point.
 
Huntxtrm said:
That's why I used 460v. I know its not nominal, but that is the voltage in the table. Why, would the NEC use voltages, that are not nominal, in a Table Anyway? Is it because that is what is generaly listed on the motor name plate?
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Essentially yes. I believe they are NEMA-specified motor voltages.
 
Huntxtrm said:
So, for safety sake. To make sure my service is not undersized. I should use 480V nomatter what is tabled or nameplated? The seems to be a grey area, to me, at this point.
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To be honest, it probably wouldn't make much of a difference, but the Code does say to use the nominal system voltage for load calculations. The Full-Load Current tables do tell you that the voltages listed are "rated motor voltages", not nominal system voltages.
 
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