Sizing Neutral (grounded conductor) for Service/Feeder

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cwain

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I am a little confused on the proper way to size a neutral feeder or service conductor. I think I understand the optional method from annex D but the standard method example D1(a) in Annex D , I'm not sure of. Can some one show me an example of both please?
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
I am a little confused on the proper way to size a neutral feeder or service conductor. I think I understand the optional method from annex D but the standard method example D1(a) in Annex D , I'm not sure of. Can some one show me an example of both please?
Have you looked at art.220.61?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
If you look at 220.61 it tells us the neutral must carry the net calculated load connected to the neutral, in the example 5100 VA. + the dryer and range which are connected to the neutral, but 220.61(B) also tells us
that in regard to the range and dryer you can use an additional demand factor of 70%, so the 8000va range is figured at 5600 (70%), likewise the dryer at 3850 va.
 

cwain

Member
So is that all there is to it. Just add the general lighting load, small appliance load,laundry load and then 70% of the range and dryer? what about dishwasher, trash compactor, garbage disposal, deep freezer, central vac system window ac units ect. Please give me more input.
 

Smart $

Esteemed Member
Location
Ohio
So is that all there is to it. Just add the general lighting load, small appliance load,laundry load and then 70% of the range and dryer? what about dishwasher, trash compactor, garbage disposal, deep freezer, central vac system window ac units ect. Please give me more input.
Regarding range and dryer loads, think about it... how much current do they contribute to the neutral when unbalanced by another circuit? They are basically line-to-line loads... and that is only if their heat source is electric. A good way to determine the neutral current is to compare to gas-heated ranges and dryers.

The gist of it is if you turned off all but one line on at a time, the maximum possible neutral current that any one line would place on the neutral is the maximum unbalanced neutral current.

If there is a panel schedule which includes (k)VA per circuit per line, just add up each line skipping over the line-to-line loads to get a total, add in your range and dryer amount, and whichever line totals the most line-to-neutral load is the maximum amount of unbalanced neutral current.
 
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Greg1707

Senior Member
Location
Alexandria, VA
Occupation
Business owner Electrical contractor
quick method

quick method

Regarding range and dryer loads, think about it... how much current do they contribute to the neutral when unbalanced by another circuit? They are basically line-to-line loads... and that is only if their heat source is electric. A good way to determine the neutral current is to compare to gas-heated ranges and dryers.

The gist of it is if you turned off all but one line on at a time, the maximum possible neutral current that any one line would place on the neutral is the maximum unbalanced neutral current.

If there is a panel schedule which includes (k)VA per circuit per line, just add up each line skipping over the line-to-line loads to get a total, add in your range and dryer amount, and whichever line totals the most line-to-neutral load is the maximum amount of unbalanced neutral current.

Regarding sizing neutral for dwelling unit services, I believe that I read somewhere that prior to 1996 the neutral was allowed to be reduced by two sizes. After that time the neutral was allowed to be reduced even more. Since SEC is commonly used what is the size AWG of the neutral in relation to the hot conductors for SEC?
 
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