Optional Residential Calc for Neutral & 4+ fixed appliances DF

[CONDUIT]

Smart $ here is the load for a single family dwelling.

2,500 sq. ft.
2 small appliance circuits
1 laundry circuit
12 kw range 120/240
5 kw dryer 120/240
1 kw dishwasher 115 volts
1 disposal 1/3 h.p. 115 volts
1 waterheater 240 volts
1 attic fan 1/4 h.p 115 volts
1 trash compactor 1/6 h.p 115 volts
15 kw electric heat 240 volts
7-1/2 h.p. a.c. unit 240 volts
Using the optional method what size ungrounded conductors would I need and using the optional method what is the minimum size ungrounded conductors and what is the minimum size grounded conductors needed.
I see that you are now steering away from the code in that the style manual specifically tells you what a "article" is as far as the code is written. I find it even more interesting that you don't even do calculation's but you are certain you are correct. I am not trying to be critical. I have taught electrical code classes for 13 years and constantly here journeyman and master electricians making statements that they have no bases for or they say something that they can't explain. I will be the first to admit that I learn new things everyday and that I am no where close to knowing everything about the code. I do make mistakes but I am confident I am correct here. Here from you soon with your calculation.

 

[HEYDOG]

The water heater is 4.5 kw.

 

[Smart $]

Smart $ here is the load for a single family dwelling.

2,500 sq. ft.
2 small appliance circuits
1 laundry circuit
12 kw range 120/240
5 kw dryer 120/240
1 kw dishwasher 115 volts
1 disposal 1/3 h.p. 115 volts
1 waterheater 240 volts
1 attic fan 1/4 h.p 115 volts
1 trash compactor 1/6 h.p 115 volts
15 kw electric heat 240 volts
7-1/2 h.p. a.c. unit 240 volts
Using the optional method what size ungrounded conductors would I need and using the optional method what is the minimum size ungrounded conductors and what is the minimum size grounded conductors needed.
I see that you are now steering away from the code in that the style manual specifically tells you what a "article" is as far as the code is written. I find it even more interesting that you don't even do calculation's but you are certain you are correct. I am not trying to be critical. I have taught electrical code classes for 13 years and constantly here journeyman and master electricians making statements that they have no bases for or they say something that they can't explain. I will be the first to admit that I learn new things everyday and that I am no where close to knowing everything about the code. I do make mistakes but I am confident I am correct here. Here from you soon with your calculation.

The water heater is 4.5 kw.

I got lucky... I put in water heater load at 4.5kW before your second post :grin:

Here ya go...

I should add that I used a method which results in the "minimum" maximum unbalanced neutral current. Can someone point out how? Is this approach compliant? If so, how should it be done? I am aware of two other, shall we say "approved" ways... I just want to see what others have to say.

BTW, HEYDOG/CONDUIT, just because I said I don't do calculations, it definitely does not mean I don't know how to do them

 

[Smart $]

....
I see that you are now steering away from the code in that the style manual specifically tells you what a "article" is as far as the code is written. ...

Well, stop asking questions that only a Code idiot could get wrong. It could be taken to be derisive.

 

[CONDUIT]

Here is what I come up with using the standard method>

2,500 x 3 = 7,500
1,500 x 2 = 3,000
1,500 x 1 = 1,500

= 12,000
3,000 @ 100% = 3,000
9,000 @ 35% = 3,150 6,150 for gen lt / sm appl

115 volt appliances 3,001 x .75 = 2,251
range 8,000 x .70 = 5,600
dryer 5,000 x .70 = 3,500
25% of disposal = 828 x .25 = 207

total = 17,708/240 = 74 amps # 4 awg at 75 c

Comes out fairly close in this instance. also for sizing the minimum ungrounded conductors for a single family dwelling look at table 310.15(b)(6). In 220.61(b) is where it talks about the neutral for household ranges and dryers can be sized at 70% based on tables 220.54 and 55. So if 220.82 refers you to 220.61 it seems like you only used the part you want to. Like I said I am constsntly learning new things about the code. The books that I have used from many of the so called experts have all went back to the standard method for sizing the neutral when they used the optional for sizing the ungrounded conductors. You just have to make sure it meets the requirements of 250.24(c). I all so double checked with a author of many code related calculation books and he all so teached NEC classes for the NFPA and he says that you use the standard method for sizing the neutral because there is no optional method. Just stating what I have seen and been told for the last 25 years.

 

[Smart $]

...

Comes out fairly close in this instance.

Yes it does... and it would even be closer using teither of the other two [optional] methods that I mentioned.

also for sizing the minimum ungrounded conductors for a single family dwelling look at table 310.15(b)(6). In 220.61(b) is where it talks about the neutral for household ranges and dryers can be sized at 70% based on tables 220.54 and 55. So if 220.82 refers you to 220.61 it seems like you only used the part you want to.

No, I did not use only the part I wanted to. The optional method does not use Tables 220.54 and .55, so 220.61(B)(1) does not apply for the optional method.

Like I said I am constsntly learning new things about the code. The books that I have used from many of the so called experts have all went back to the standard method for sizing the neutral when they used the optional for sizing the ungrounded conductors. You just have to make sure it meets the requirements of 250.24(c). I all so double checked with a author of many code related calculation books and he all so teached NEC classes for the NFPA and he says that you use the standard method for sizing the neutral because there is no optional method. Just stating what I have seen and been told for the last 25 years.

I am aware of other "experts" using the optional method for the ungrounded and standard method for the neutral. Even the examples of Annex D use the standard for neutral calc's. IMO, it's a contradiction of terms.

220.61 says, "The feeder or service neutral load shall be the maximum unbalance of the load determined by this article. The maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one ungrounded conductor." I don't see how you can use one method to determine the load on the ungrounded conductors and then use a different method to determine the load between the neutral and one of the same ungrounded conductors. Well, I should say I see how it is done... in reality the load (not the calculated load) is the same. What I really mean is that I just don't see how it compliantly correlates with the wording of 220.61(A) and 220.82(A).

 

[Little Bill]

I got lucky... I put in water heater load at 4.5kW before your second post :grin:

Here ya go...

I should add that I used a method which results in the "minimum" maximum unbalanced neutral current. Can someone point out how? Is this approach compliant? If so, how should it be done? I am aware of two other, shall we say "approved" ways... I just want to see what others have to say.

BTW, HEYDOG/CONDUIT, just because I said I don't do calculations, it definitely does not mean I don't know how to do them

Hey Smart $,
Why couldn't you use Table 310.15 (B)(6) to size the conductors? The 126.5A would be rounded up to 150A and the table says you can use #1 AWG. That is, if this is a dwelling.

 

[Smart $]

Hey Smart $,
Why couldn't you use Table 310.15 (B)(6) to size the conductors? The 126.5A would be rounded up to 150A and the table says you can use #1 AWG. That is, if this is a dwelling.

Could. I forgot about that.

 

[Little Bill]

Could. I forgot about that.

Thanks, I feel better now! I guess even a blind squirrel (me) can find a nut every now and then!

 

[HEYDOG]

Smart$. How can you be so certain that your interpretation of 220.82 and 220.61 are correct. As I stated, and you all so said, that many so called code experts show using the standard method for sizing the neutral when they use the optional method. I also mentioned that I talked to an instructor that teaches for the NFPA. I just find it odd that a instructor that teaches the National Electrical Code for the NFPA and has written many of his on books and also has written many calculation articles for a major electrical trades magazine could be totally wrong. I do not know how any one in the field can possibly apply the code correctly if this is true. I know that I will always verify the neutral is capable of carrying the unbalanced current. I believe that in my area this is why most inspectors will not let you downsize the neutral. If they require you to install a full size neutral they do not have to worry about whether your calculation is correct or not. Just curious if you have written in a proposal to clarify these particular sections (article) since you say that it is not being interpreted correctly by more people than just myself. I have not done neutral calculations using the optional method but may have to try several to see if they all come out as close as the example we worked. In that one the neutral using the standard method actually had to be good for a few more amps even though it was the same wire size. The other thing that you state is that I can not mix calculation methods. If the neutral is big enough when I use the standard method I would certainly think it would be big enough for the load if I use the optional method.

 

[Little Bill]

I know I don't have a dog in this race but please allow me to add this little bit to your discussion. Although I've been doing electrical (mostly industrial and control) for over 20 years I'm not extremely familiar with the code. However, I've just finished Mike Holt's NEC Exam Preparation. From what he has to say about standard and optional calculating methods is that they are two distinctly different calculating methods and one should be careful not to intermix them. I think Mike Holt would be expert enough to listen to on this subject.
Now my own understanding of this to address the OP's question about using 220.53 in the optional method. The standard method allows 100% of the first 3000VA and only 35% of the remaining calculated loads for general lighting. 220.53 allows you to apply 75% DF for 4 or more fixed appliances, 120V or 240V. In the optional method, all the appliances are included in the general load calculations but you get a 40% DF after the first 10000VA. You are getting a reduction in which ever method is used. The optional method is usually a lot faster and easier to apply and has a advantage for daily use in the field. 220.61 can be used in either method for sizing the neutral, but only after calculating the entire load using 1 or the other method but not mixing them. If you could intermix them there would be no need of having 2 methods.

 

[Smart $]

Smart$. How can you be so certain that your interpretation of 220.82 and 220.61 are correct. As I stated, and you all so said, that many so called code experts show using the standard method for sizing the neutral when they use the optional method. I also mentioned that I talked to an instructor that teaches for the NFPA. I just find it odd that a instructor that teaches the National Electrical Code for the NFPA and has written many of his on books and also has written many calculation articles for a major electrical trades magazine could be totally wrong. I do not know how any one in the field can possibly apply the code correctly if this is true. I know that I will always verify the neutral is capable of carrying the unbalanced current. I believe that in my area this is why most inspectors will not let you downsize the neutral. If they require you to install a full size neutral they do not have to worry about whether your calculation is correct or not. Just curious if you have written in a proposal to clarify these particular sections (article) since you say that it is not being interpreted correctly by more people than just myself. I have not done neutral calculations using the optional method but may have to try several to see if they all come out as close as the example we worked. In that one the neutral using the standard method actually had to be good for a few more amps even though it was the same wire size. The other thing that you state is that I can not mix calculation methods. If the neutral is big enough when I use the standard method I would certainly think it would be big enough for the load if I use the optional method.

Little Bill's reply is as good as any. For myself, all I have to stand on is the wording of the Code. I consider myself fairly good at [literally] interpretting Code. Not so much for reading CMP members minds (i.e. intent), or always having a desire to look up Report on Proposals concerning the issue to determine intent. Nonetheless, the Code says what it says, regardless of intent. Why should someone have to resort to other literature and documentation that have not been adopted into law to determine intent. And even doing so does not change the fact as to which documents are law and which are not.

In many cases, the wording of the Code does not match the intent... and there is usually some improvement each cycle, but with a three-year cycle, the process is slow. Another thing is that most of the so-called experts are not open to someone saying the Code actually something different than what they believe is the intent (including the CMP members). I don't know if they are among the literarily challenged or just have self-inflated egos. It don't matter 'cause it all boils down to being what it is, and will take a concerted effort by those in control to change it.

 

[Smart $]

Accidently hit the Submit button before I intended... so even I am capable of doing something that doesn't clearly express my intent

... Just curious if you have written in a proposal to clarify these particular sections (article) since you say that it is not being interpreted correctly by more people than just myself. ... If the neutral is big enough when I use the standard method I would certainly think it would be big enough for the load if I use the optional method.

No I have not written a proposal for such. For the same reason you state, I do not believe a major problem exists. If those doing the calc's want to do two methods worth of calc's, let 'em.

I have not done neutral calculations using the optional method but may have to try several to see if they all come out as close as the example we worked. In that one the neutral using the standard method actually had to be good for a few more amps even though it was the same wire size. The other thing that you state is that I can not mix calculation methods.

Sure... try it and see what you come up with. One thing about the example is you didn't show the calc' for the ungrounded. I believe grounded to ungrounded for each method is a better comparison.

Also, I mentioned two other [slightly different] methods to performing the optional neutral calc'. They likely would yield a higher calc' result for the neutral load. I'll try to get them posted for review here soon...

 

[Smart $]

....

Also, I mentioned two other [slightly different] methods to performing the optional neutral calc'. They likely would yield a higher calc' result for the neutral load. I'll try to get them posted for review here soon...

Here they are...

(Note: 18,60VA in the upper method supposed to be 18,061VA.)

 

[Smart $]

Smart$. How can you be so certain that your interpretation of 220.82 and 220.61 are correct. ...

Refer to 230.42(A) where it says, and I quote, "Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable." This was a 2008 NEC addition. Note it does not say "...in accordance with Part III, IV, and V..."

 

[CONDUIT]

If the code is adopted into law I guarantee that both sides will not rely on the wording of the code alone. They will call in many of the so called code experts to get a understanding of the intent of the code. I know several of the authors of code related books are also expert witnesses in code related cases. I agree that I will always make sure the neutral is of the proper size to carry the maximum unbalanced current. The problem is when electricians take the journeyman or masters they have to determined the proper method to come up with the answer that the writter of the test is looking for based on what method they used to determine the size of the neutral. Here again it depends on the knowledge on the test writter and whether it is right or wrong may not meet the intent of the code. This whole discussion is really not that big of deal as long as the neutral is sized large enough for the maximum unbalanced load. The biggest issue I have is that many electricians come through my classes that are preparing to take their masters or journeyman and I want to make sure I am giving them accurate information. I do not think that you answered my question as to if the neutral is sized large enough when using the standard method wouldn't it still be large enough if I used the optional method for sizing the ungrounded conductors? If not why other than just saying it isn't permissible by code the way that you interpret it? I have enjoyed this discussion whether we agree are not. As I have stated in the field I am going to check several different ways to make sure it is not undersized. It is more of a concern when teaching proper methods of using the code to others.

 

[Smart $]

If the code is adopted into law I guarantee that both sides will not rely on the wording of the code alone. They will call in many of the so called code experts to get a understanding of the intent of the code. I know several of the authors of code related books are also expert witnesses in code related cases.

In a court case, yes. It would not be prudent for either or all parties not to. And relying on so-called experts for an interpretation other than written word also proves the Code in many instances does not project the exact intent of its purpose, opens an avenue for precedence, and so on...

But we're surely not going to get into the procedural effects and remedial actions of courtcases here in this forum, regardless of our viewpoints.

I agree that I will always make sure the neutral is of the proper size to carry the maximum unbalanced current.

Is using either method a certainity? ...or a best guess with padding? I believe using either method is the latter.

The problem is when electricians take the journeyman or masters they have to determined the proper method to come up with the answer that the writter of the test is looking for based on what method they used to determine the size of the neutral. Here again it depends on the knowledge on the test writter and whether it is right or wrong may not meet the intent of the code.

Agreed.

This whole discussion is really not that big of deal as long as the neutral is sized large enough for the maximum unbalanced load. The biggest issue I have is that many electricians come through my classes that are preparing to take their masters or journeyman and I want to make sure I am giving them accurate information.

You seem professional enough that I would expect nothing less

I do not think that you answered my question as to if the neutral is sized large enough when using the standard method wouldn't it still be large enough if I used the optional method for sizing the ungrounded conductors?

Well, I did answer, though implicitly. Explicitly, either method should be fine. If you want certainty, disregard any demand allowances and use either method (this will amount to the same result). The application of demand factors are permissible, not required.

If not why other than just saying it isn't permissible by code the way that you interpret it?

Given my immediately preceding answer, I believe this question to be moot.

I have enjoyed this discussion whether we agree are not. As I have stated in the field I am going to check several different ways to make sure it is not undersized. It is more of a concern when teaching proper methods of using the code to others.

I agree proper methods are best... but the Code text should expound on the detail of what is proper... and it fails in this respect if your "way" is the only one that is proper.

 

[LarryFine]

Hey Smart $,
Why couldn't you use Table 310.15 (B)(6) to size the conductors? The 126.5A would be rounded up to 150A and the table says you can use #1 AWG. That is, if this is a dwelling.

You're always permitted to size the service larger than required.

 

[Finite10]

Last edited by gndrod; 01-03-11 at 11:22 AM. Reason: Note that the largest motor 25% is not figured as it is part of the FIP motors in [220.82][220784] DF

That clears things up thanks, I wondered about that in the Optional method.

 

[Finite10]

SF Optional

SF Optional

Here's what I did; SF Opt.

Gen light 100%
2 sm appl 100%
Laundry 100%
Range 120/240V npr
dryer 120/240V npr
fixd appl 120V npr
Wtr Htr 240V npr
_______________________
Total 1

Total 1 - 10,000VA @ 100% = Total 2

Total 2 @ 40% = Total 3

Largest of: AC or heat = Total 4

10,000VA + Total 3 + Total 4 = Grand Total Ungrounded
...................................................................................
Neutral:
Gen light + sm appl + laundry; 3,000 @ 100% + <117,000 @ 35% = Total 1

Dryer and Range @ 220.53 & 220.55, then @ 220.61 70% = Total 2

4+ fixed appl 120V only @ npr = Total 3

Total 1 + Total 2 + Total 3 = Grand Total Grounded
................................................................................

*http://forums.mikeholt.com/showthread.php/133044-2-very-odd-questions-I-thought
Could the collective wisdom here look at this. The exam said to omit laundry in Multi Family Opt calcs- which I did per 210.52(F). But my answers didn't match the exam's. Dryer not on eqip. list or mentioned at all.
http://forums.mikeholt.com/showthread.php/133044-2-very-odd-questions-I-thought