Why full size neutral single phase?

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Consider a 200A residential service with 20 or more nondedicated recepticle circuits. By plugging in 20A of loads into 10 of the circuits (which by chance are all on the same leg), you can fully load the neutral.

Sure, it will never happen in practice, but it's mathematically possible.
 
Gene B said:
Consider a 200A residential service with 20 or more nondedicated recepticle circuits. By plugging in 20A of loads into 10 of the circuits (which by chance are all on the same leg), you can fully load the neutral.

Sure, it will never happen in practice, but it's mathematically possible.
Click to expand...

I prefer to live in the world of reality. If the code allows it, I'm doing it.
 
One reason to consider NOT reducing the neutral is harmonics caused by non-linear loads. Odd order harmonics are additive in single phase circuits and flow in the neutrals, causing more heating per unit of fundamental current flow. When the majority of residential loads were linear (incandescent lighting, resistance heating, single speed motors) there wasn't enough THD in residential to worry about. But now almost EVERYTHING has a non-linear Switch Mode Power Supply; PCs, TVs, sound systems, video systems, security systems, chargers, UPSs, even some of the traditional linear loads like washers and dryers (which now have VFDs inside). Plus we have done away with incandescent for lighting, so even that is now ALL non-linear. The old rule of thumb was if 30% or more of your total load was non-linear, you needed to be concerned about harmonic loading. In a lot of cases, residential installations are now exceeding that. Using the same size neutral is a safer bet against causing over heating even though it's not required.
 
mivey said:
Well, not really. What jaggedben described was all the current in the ungrounded conductor matching the grounded conductor current. Pretty easy for that to happen.

To max out the grounded conductor ampacity and have that current matched in the grounded conductor as you propose is something different. To do that you have to get rid of all the 240 volt loads. Then you have to overload one side of the 120 volt circuits. Is that the kind of scenario you really want to propose? That sounds like a poster you have argued against here for making similarly outlandish statements.
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OK.
Suppose there are no 240V loads.
Half the 120V loads are on one of the lives, say A and Half on B. Balanced and presumably compliant? Now turn off, and/or unplug all the loads on B and leave on all the loads on A.
Wouldn't the current in the neutral be that same as that flowing in A?
 
Besoeker said:
OK.
Suppose there are no 240V loads.
Half the 120V loads are on one of the lives, say A and Half on B. Balanced and presumably compliant? Now turn off, and/or unplug all the loads on B and leave on all the loads on A.
Wouldn't the current in the neutral be that same as that flowing in A?
Click to expand...
Yes. For a typical dwelling it will seldom draw over 60-75 amps of load even if you put all the 120 volt loads on A. It is the 240 volt appliances that push the need for over 100 amp supply conductors in the average to below average sized dwellings in most instances, exception might be if you had a lot of 120 volt space heating or cooling units, water heating or larger cooking appliances, but those typically are 240 volt units.
 
I did hear of an incident in a school building one time where they ran three banks of lights in all the classrooms, Line A supplied the front of the room, B the middle and C the back (or something similar to that). Problem was before /after hours maintenance would come in and turn on the front row in all rooms and nothing else. These lights maybe even remained on during the day when a room wasn't in use. This put all of that load on line A and limited loads on other two lines. Over time this apparently did cause neutral issues, but was not a situation ever planned for. The plan was load balancing when all the lights were in use

Now I can't believe that lighting was that significant of a load to cause this problem when there was probably more HVAC load then lighting, and that HVAC load was more likely to be more balanced, but this is a story I was told and not something I personally witnessed.
 
Cletis said:
Just curious why everyone runs or installs full size neutrals in service conductors residential since it generally will only carry 1/2 the load of 120v items ??

Ex. I ran 4/0,4/0,1/0 alum service one time and inspector wouldnt pass. I tried to explain max nuetral load to him but that pissed him off even more
Click to expand...
.
everyone doesn't. if you take a peek at SER cable in the big box stores, it is 4/0,4/0, and 2/0.

and you want to save the difference between 2/0 and 1/0 aluminum, on 20' of material?

it amounts to $2.80. there are fifty two (not counting this one) responses to this thread,
making each one of them worth $.05..... i'm not counting my response as having any value
at all.

i'm sensing a tendency to troll the forum here.
are you actually installing services with so little profit that $2.80 matters? really?
 
Fulthrotl said:
.
everyone doesn't. if you take a peek at SER cable in the big box stores, it is 4/0,4/0, and 2/0.

and you want to save the difference between 2/0 and 1/0 aluminum, on 20' of material?

it amounts to $2.80. there are fifty two (not counting this one) responses to this thread,
making each one of them worth $.05..... i'm not counting my response as having any value
at all.

i'm sensing a tendency to troll the forum here.
are you actually installing services with so little profit that $2.80 matters? really?
Click to expand...

We all know free advice is usually worth what you pay for it so that .05 is pretty dang high.
 
Fulthrotl said:
.
everyone doesn't. if you take a peek at SER cable in the big box stores, it is 4/0,4/0, and 2/0.

and you want to save the difference between 2/0 and 1/0 aluminum, on 20' of material?

it amounts to $2.80. there are fifty two (not counting this one) responses to this thread,
making each one of them worth $.05..... i'm not counting my response as having any value
at all.

i'm sensing a tendency to troll the forum here.
are you actually installing services with so little profit that $2.80 matters? really?
Click to expand...

For me the issue is NOT the $2.80 profit. I don't know how to phrase my reason but here is the way that I look at it. Would I take out $2.80 from my pocket and just throw it away? NO i would not. Then why should I spend $2.80 on wire that I don'r have to.

Besides it gives something to debate about when the inspector shows up.
 
Besoeker said:
OK.
Suppose there are no 240V loads.
Half the 120V loads are on one of the lives, say A and Half on B. Balanced and presumably compliant? Now turn off, and/or unplug all the loads on B and leave on all the loads on A.
Wouldn't the current in the neutral be that same as that flowing in A?
Click to expand...
I suppose we can discuss something different than what the OP was talking about but that could run over into almost anything.

Now are you really wanting validation that on a two-wire circuit the current in one conductor is the same as in the other conductor? How far away from the OP scenario do you plan to go?
 
Besoeker said:
OK.
Suppose there are no 240V loads.
Half the 120V loads are on one of the lives, say A and Half on B. Balanced and presumably compliant? Now turn off, and/or unplug all the loads on B and leave on all the loads on A.
Wouldn't the current in the neutral be that same as that flowing in A?
Click to expand...

Yes that is true what ever flows on A will flow on the neutral.

Now the chances of that happening are very rare. If it does happen it will not be in a high enough current that will overload the service neutral or even the feeder neutral.
 
Fulthrotl said:
.
everyone doesn't. if you take a peek at SER cable in the big box stores, it is 4/0,4/0, and 2/0.

and you want to save the difference between 2/0 and 1/0 aluminum, on 20' of material?

it amounts to $2.80. there are fifty two (not counting this one) responses to this thread,
making each one of them worth $.05..... i'm not counting my response as having any value
at all.

i'm sensing a tendency to troll the forum here.
are you actually installing services with so little profit that $2.80 matters? really?
Click to expand...

What about a large job with hundreds or thousands of feet of large wire?
 
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