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Old 02-20-2010, 07:25 PM   #1
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Discussion on reduced Neutral


So Nap does the NEC allow any type of reduced neutral for residential or is it always a full size neutral.

That is one thing i like about this site, you get to learn how things are done south of the border, in your case north of the border.
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Old 02-20-2010, 07:59 PM   #2
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I do not believe so. It has been 10-15 years since I installed a residential service or a service under 400 amps so what happens in residential sometimes gets past me.

Something sticks in my head about reduced neutrals but I believe, if it was there, it is now gone.

Hopefully one of the other guys that does more residential stuff can step in on this question.

Now, as I noted before, they allow undersized conductors (hots and neutrals) fro a residential service but nothing close to a #6 for 200 amp. It sounds like you folks have the same allowances up north; 2/0 cu or 4/0 al for a 200 amp service.
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Old 02-20-2010, 08:54 PM   #3
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For single phase services, the neutral conductor may be reduced to match the maximum net calculated unbalanced load.

The limitation is the neutral may not be reduced beyond that normally required for a grounding electrode conductor for the same size service.

This means that on a typical 200 Amp service fed with 2/0 copper conductors, the neutral could be as small as a #4, provided your unbalanced load calculations do not exceed 85 Amps. I have yet to see one that comes anywhere close to this value.

We typically use a #0 or #1 neutral conductor on 200 Amp services, fed with 2/0 copper hot conductors.
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Old 02-20-2010, 10:04 PM   #4
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Discussion on reduced Neutral


Quote:
Originally Posted by kbsparky View Post
For single phase services, the neutral conductor may be reduced to match the maximum net calculated unbalanced load.

The limitation is the neutral may not be reduced beyond that normally required for a grounding electrode conductor for the same size service.

This means that on a typical 200 Amp service fed with 2/0 copper conductors, the neutral could be as small as a #4, provided your unbalanced load calculations do not exceed 85 Amps. I have yet to see one that comes anywhere close to this value.

We typically use a #0 or #1 neutral conductor on 200 Amp services, fed with 2/0 copper hot conductors.
have you got a code section for the kbsparky? I have not seen anything that would allow it but that does basically sound like what the canucks have. Definitely interested in advancing my knowledge
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Old 02-20-2010, 10:24 PM   #5
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Quote:
Originally Posted by nap View Post
most likely the POCO is running 4/0 aluminum, not copper. That would be the proper size for 200 amp.

in our NEC, we have a section (table 310.15 B 6) that allows the wire to be undersized for a residential service. I am guessing you have something similar in the CEC.


Darren, you didn't really mean this did you?



In the US a #6 would be good for a GEC to certain grounding electrodes but it is not a one size fits all in all situations and I do not believe you meant to infer the neutral can be a #6, or at least I hope. I suspect you were referring to the GEC. The neutral, unless you allow a reduced neutral, would have to be 2/0 cu just line the other service conductors.

at least in the US.
Without having any NEC Table reference at hand, I recall that a 200 Amp. Main (which I've done numerous ones) requires a .000/AWG (Three Odd) size wire. As one of the posters pointed out, the .0000/AWG that the Poco used for a 200 Amp. Service, is aluminum. They usually undersize Services.
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Old 02-20-2010, 10:39 PM   #6
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Quote:
Originally Posted by spark plug View Post
Without having any NEC Table reference at hand, I recall that a 200 Amp. Main (which I've done numerous ones) requires a .000/AWG (Three Odd) size wire. As one of the posters pointed out, the .0000/AWG that the Poco used for a 200 Amp. Service, is aluminum. They usually undersize Services.
I do have a code book at hand and I still cannot find anything that would allow the reduced neutral.

when using 2/0 cu or 4/0 al, that is already undersized. 2/0 cu is rated for 175 amps ans 4/0 al is rated for 180 amps.

and those sizes are specifically allowed per table 310.15(B)(6) for a resi service
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Old 02-20-2010, 10:57 PM   #7
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Quote:
Originally Posted by nap View Post
I do have a code book at hand and I still cannot find anything that would allow the reduced neutral.

when using 2/0 cu or 4/0 al, that is already undersized. 2/0 cu is rated for 175 amps ans 4/0 al is rated for 180 amps.

and those sizes are specifically allowed per table 310.15(B)(6) for a resi service
I wasn't referring to the Undersized Neutral, which I agree with you. My reference was that a 200A. Service would require higher than 2/0 Cu. or 4/0 Al. And that the utilities (POCO) are notorious for undersizing Services (at least the local utility does. Please C.E. don't call me about it!) Ostensibly arguing that their wires are of a higher quality and can take the (potential) overload!
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Old 02-20-2010, 11:09 PM   #8
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Quote:
Originally Posted by spark plug View Post
I wasn't referring to the Undersized Neutral, which I agree with you. My reference was that a 200A. Service would require higher than 2/0 Cu. or 4/0 Al. And that the utilities (POCO) are notorious for undersizing Services (at least the local utility does. Please C.E. don't call me about it!) Ostensibly arguing that their wires are of a higher quality and can take the (potential) overload!
yes, that is exactly what I said. It would appear we are on the same page with that.

those conductors are under size as the cu is rated 175 amps and the al is rated 180 amps.

if the conductors were not allowed to be undersized, then it would require; 3/0 cu or 250 mcm al.


so, kbsparky, if you have some direction, I would be more than glad to do some looking but I haven't had any luck yet about the extremely undersized and reduced (as compared to the hot legs) neutral.
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Old 02-21-2010, 08:30 AM   #9
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First, take a look at section 220.61 which covers the load calculations for the feeder or service neutral conductor. This is where they require the neutral to be able to handle the maximum unbalanced load.

Next, let's evaluate section 250.24(C)(1) which covers the grounded (neutral) conductor's minimum size to be no smaller than the required grounding electrode conductor specified in table 250.66. Here you also will find that on very large services, the neutral conductor must be at least 12% as large as the phase conductors. That is 1/8 as large as the ungrounded conductors.

Even though you may be able to use a #6 copper grounding electrode conductor on a ground rod for a 200 Amp service, the value in table 250.66 requires a #4 on services fed with a 2/0 or 3/0 conductor. That exception appears in the text of 250.66(A). This exception does not apply to the neutral conductor which was referenced in 250.24(C)(1).
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Old 02-21-2010, 11:40 AM   #10
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220 is for calculations to determine the required service size. .61 cannot be used to determine feeder size. It just is not the purpose of the chapter.


but, let's presume it did actually allow you to determine neutral size. Before any reduction could be allowed, you would have to do an actual load calculation AND if you notice, 220.60(B) allows only 2 limited situations where such an over capacity of the conductor is allowed.




but again, let's presume that would allow you to determine the ampacity of the grounded conductor. 220.61 (B) gives you an allowed over ampacity of 70%. That would mean on a 200 amp service, you would still be limited to using a conductor with an ampacity of at least 118 amps. (200/1.7) so you would be limited to at least #1 cu. Still a far cry from the #6 tossed about in this thread.


the 250 section alludes there may be an allowance and simply provides clarification as to the minimum and maximum of the grounded conductor if some other section allows a less than full sized neutral. It does not infer any specific allowance of variation from the ungrounded conductors. It does not allow for any reduction in itself, merely sets limits.



Quote:
Even though you may be able to use a #6 copper grounding electrode conductor on a ground rod for a 200 Amp service, the value in table 250.66 requires a #4 on services fed with a 2/0 or 3/0 conductor. That exception appears in the text of 250.66(A). This exception does not apply to the neutral conductor which was referenced in 250.24(C)(1).
not sure what you are after here. 250.66(A) allows the #6 to rods, pipes, and plates and I stated this before.
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Old 02-21-2010, 11:43 AM   #11
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Quote:
Originally Posted by spark plug View Post
I'm certain, there's a link to active CEC. One of the DIY'rs/Electricians from Canada should be able to help you. Good Luck.!
If somebody knows of a link to a recent copy of the CEC, that would be great. We have enough questions about Canadian rules that something like that would be very useful.
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Old 02-21-2010, 12:52 PM   #12
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nap i doubt if they put it on the internet for free, they charge us 150 to have the pleasure to own the book. The code book used to be updated every 4 years but they just changed that to every 3 years, anyway to get more money out of you.

One other thing to note, our 2/0Cu is good for 185A, how can that be differnt then the USA, is not all copper made the same or do they make special stuff for us Canadians. Or do they think we live in igloos where it never gets hot so even if the wire gets warm the surronding air temp will keep the wire cooler.

To the OP, are you doing an overhead or an underground installation?
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Old 02-21-2010, 02:50 PM   #13
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Quote:
Originally Posted by nap View Post
220 is for calculations to determine the required service size. .61 cannot be used to determine feeder size. It just is not the purpose of the chapter....
Section 220.61 is titled Feeder or Service Neutral Load ! It is the purpose of this section to determine feeder loads. The fact that the neutral loads are mentioned at all indicates that the size of this particular feeder conductor may be determined by using this section. Otherwise, it would be a moot point.

Quote:
but, let's presume it did actually allow you to determine neutral size. Before any reduction could be allowed, you would have to do an actual load calculation AND if you notice, 220.60(B) allows only 2 limited situations where such an over capacity of the conductor is allowed.

but again, let's presume that would allow you to determine the ampacity of the grounded conductor. 220.61 (B) gives you an allowed over ampacity of 70%. That would mean on a 200 amp service, you would still be limited to using a conductor with an ampacity of at least 118 amps. (200/1.7) so you would be limited to at least #1 cu. Still a far cry from the #6 tossed about in this thread....
Let's read this section in more detail: In 220.61(A) it talks about Basic Calculations. It is here that the max unbalanced load is determined. In sub-section (B), it allows for an additional 70 percent demand factor applied if the loads include things like ranges, ovens, or dryers on top of the basic calculations performed in sub-section (A).

Quote:

the 250 section alludes there may be an allowance and simply provides clarification as to the minimum and maximum of the grounded conductor if some other section allows a less than full sized neutral. It does not infer any specific allowance of variation from the ungrounded conductors. It does not allow for any reduction in itself, merely sets limits....
Again, no mention would be necessary if no reductions were allowed. Since reductions are allowable, limits to those reductions are set forth in this section.

Quote:
not sure what you are after here. 250.66(A) allows the #6 to rods, pipes, and plates and I stated this before.
There was a reference to the CEC allowing a #6 neutral here. My inclusion of this paragraph was to show the slight differences between the NEC and CEC along these lines; and to show that even if one were to use a #6 GEC when using a ground rod electrode, table 250.66 still would require a minimum #4 neutral on a 200 Amp service fed with a 2/0 or 3/0 conductor.
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Old 02-21-2010, 10:26 PM   #14
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so, you thing you are right?

post service installation that would allow you to use a #4 neutral on a 200 amp service. Even with your argument, it is not available on all 200 amp services so post an installation that would allow it.
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Old 02-22-2010, 07:37 PM   #15
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One requirement of holding a master's electrical license around here is that we are compelled to take continuing education classes. These classes are mainly administered by the local inspection agencies, who have Code experts on staff that evaluate the NEC and develop the courses for continuing education requirements. These courses are then approved by the licensing electrical boards, before being offered to the license holders.

This very topic was discussed in detail at one such seminar given last year, citing the Code sections that I have mentioned here for you. I did not believe that one could possibly have such a reduced neutral on a typical 200 Amp service, either. The Code is a minimum standard, and most folks would not install a neutral as reduced as we have been discussing.

Hwever, here is one article on this subject. In it, there is an example where the neutral conductor of a 400 Amp service is only required to be a #3, due to the limited neutral loads.
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