Neutral Conductor Sizing

[wbryan09]

I've read in detail all the posts about when you can and can not reduce the size of the grounded conductor (Neutral) . . . what I can't find is reassurance that once I make the decision about the unbalanced neutral load that I need to size that conductor based on:

Table 310.16. (It lists USE cable but not SE)

OR

Table 310.15.B.6 (for 3-wire Single Phase Dwelling Services; including SE)

Is there some distinction that leads to the use of 310.16 as opposed to 310.15.B.6?

 

[jwjrw]

310.15 b(6) is used to size your main feeder to your meter.
310.16 is used to size the feeder to the first disconnect
If that is what you are asking

 

[Buck Parrish]

It can be confusing see here http://forums.mikeholt.com/showthread.php?t=122627

 

[Dennis Alwon]

Table 310.16. (It lists USE cable but not SE

Article 338 is for se and use.

T. 310.16 would base the ampacity of USE on 90C. SE cable can be either 90C or 60C depending on the installation. Read art. 338.10(B)(4)

 

[George Stolz]

310.15 b(6) is used to size your main feeder to your meter.
310.16 is used to size the feeder to the first disconnect

Huh? :-?

...what I can't find is reassurance that once I make the decision about the unbalanced neutral load that I need to size that conductor based on...

There are no ampacities listed in Table 310.15(B)(6). A grounded conductor is not connected to overcurrent protection, so the table doesn't really apply.

220.61 requires the neutral conductor ampacity to equal or exceed the maximum unbalanced load to any ungrounded conductor. It's size would be determined by looking at 310.16.

There should not be any real world scenario where the grounded conductor size exceeds the ungrounded conductors in a dwelling unit. Your neutral conductor would almost always be allowed to be smaller.

 

[jwjrw]

Huh? :-?


There are no ampacities listed in Table 310.15(B)(6). A grounded conductor is not connected to overcurrent protection, so the table doesn't really apply.

220.61 requires the neutral conductor ampacity to equal or exceed the maximum unbalanced load to any ungrounded conductor. It's size would be determined by looking at 310.16.

There should not be any real world scenario where the grounded conductor size exceeds the ungrounded conductors in a dwelling unit. Your neutral conductor would almost always be allowed to be smaller.

I saw it coming.. I meant if you run ser inside you can no longer use it at 75 deg.

And he confused me with the neutral part

 

[George Stolz]

I saw it coming.. I meant if you run ser inside you can no longer use it at 75 deg.

Probably for this cycle only. Folks jumped out of the woodwork this cycle to protest that change, which was made in the 2008 without technical substantiation. As of ROP printing, the 2011 will return the exception to 334.80 from 338.10(B)(4).

Regardless, Table 310.15(B)(6) does not directly correspond to ampacity values of any degree column.

I believe that if my main power feeder is supplying all of the circuits in a house, I can use a #2 AL SE-R inside the home, regardless of what 338.10(B)(4) states. I'm specifically permitted to exceed the conductor ampacity in that instance, by 310.15(B)(6). What do you think?

 

[Dennis Alwon]

I believe that if my main power feeder is supplying all of the circuits in a house, I can use a #2 AL SE-R inside the home, regardless of what 338.10(B)(4) states. I'm specifically permitted to exceed the conductor ampacity in that instance, by 310.15(B)(6). What do you think?

I think your nuts but that's not what you were asking. :grin:
Actually I am in totally agreement with you on this. Gus seems to be the big dissenter on this issue. Let's pick on him.

 

[jwjrw]

Probably for this cycle only. Folks jumped out of the woodwork this cycle to protest that change, which was made in the 2008 without technical substantiation. As of ROP printing, the 2011 will return the exception to 334.80 from 338.10(B)(4).

Regardless, Table 310.15(B)(6) does not directly correspond to ampacity values of any degree column.

I believe that if my main power feeder is supplying all of the circuits in a house, I can use a #2 AL SE-R inside the home, regardless of what 338.10(B)(4) states. I'm specifically permitted to exceed the conductor ampacity in that instance, by 310.15(B)(6). What do you think?

First I keep getting conflicting answers about the exception coming back
I cant say for sure which person said it was still there in 2011. Could of been any of the usal suspects in a thread last week or I MISS READ IT.


I tend to view it like you do but I think it was Dennis that had me doubt my own opinion. Alot of you have many years debating what the code allows and it is a big help in learning at least for me. At this point Ill go with how my ahj views it....Which I believe is 310.16


Maybe it was Gus sorry!!!

 

[George Stolz]

First I keep getting conflicting answers about the exception coming back
I cant say for sure which person said it was still there in 2011.

Well, it's difficult to say, they haven't printed it yet.

 

[augie47]

I think your nuts but that's not what you were asking. :grin:
Actually I am in totally agreement with you on this. Gus seems to be the big dissenter on this issue. Let's pick on him.

Can we not discuss my weight and just say I'm the most vocal dissenter :grin:

Although, it is my conviction, I mainly speak out as there are others who agree and the also inspect. I want those who come here to know there is another view being enforced.

From what I see so far in 2011, it isn't resolved.