Why full size neutral single phase?

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Cletis

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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


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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


Sent from my iPhone using Tapatalk
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We usually reduce neutrals so it must not be everyone.
 
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


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That neutral can be as small as the minimum grounding electrode conductor - if you can provide load calculations that will show it will never be loaded more then that. For a feeder it can't be any smaller then the minimum required equipment grounding conductor.

Dwellings is a little complex to come up with a true maximum load for the neutral. Most inspectors around here will allow two sizes smaller then the ungrounded conductors without any questions on 120/240 single phase - if you have a 208/120 system you must be same size if only using two ungrounded and a neutral in most cases.

If you have a significant amount of straight 240 volt load though you can disregard all of that load when calculating the neutral.
Say you had 240 volt heating/cooling, water heater, maybe a water well - you can disregard neutral load for all of those because they don't have one, but they do use up some of your service capacity so you can't load what capacity remains with what those take up.

I have grain storage bins that I have wired with 400 amp service, the only neutral loads is a few 120 volt receptacles - most of which are just for power tools or other convenience and are seldom used, and maybe some 120 volt lighting usually only one, maybe two 15 or 20 amp branch circuits. The line to line load may be 60-80 percent of the service capacity, the loads connected to neutral are well under the what the minimum required GEC size can handle. I sure hope I would never get an inspector on such a project that can't see this neutral has nearly no load in comparison to the ungrounded conductors without seeing calculations first.
 
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 ??
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Everyone doesn't.

Cletis said:
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
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You pointed out his ignorance. Some people take that harder than others, especially if you don't sugar-coat it. Unfortunately, you never know how much sugar it takes to cover a particular person's thin skin.

Now you could have fought it out if you were feeling your oats that day and might have won if you reached the right authority or worked some golden diplomacy on the failing inspector.

Still is irritating at first.
 
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...

What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
 
Besoeker said:
What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
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Yes. But like I mentioned earlier often times there is significant connected load that doesn't utilize the neutral conductor. If you are sizing the ungrounded conductors based on the total load, only a portion of it utilizes the neutral therefore the neutral only needs to be sized in accordance with the maximum possible unbalanced loading that the neutral will see. Let's stick with simple 120/240 single phase three wire for the moment - if you have 200 amp service with 90 amps of straight 240 volt loads, you are left with a maximum of 110 amps of unbalanced neutral before even considering what 120 volts loads even exist, no need for the neutral to be able to carry more then 110 amps in this case without further calculations.
 
Besoeker said:
What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
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It would, and while it is possible, it is certainly improbable. Running enough 120V loads on one leg to overload a 2/0 neutral w/o having any load on the other leg? I dont think I could physically plug in or operate enough things here to do that to a 125A service, not w/o overloading the branch circuits in the process. Maybe a 200A panel with a lot of individual branch circuits..
 
Besoeker said:
What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
Click to expand...
George's reply isn't all that obvious in intent, especially with your being from across-the-pond and all. What it means that residential services typically have enough line-to-line load that neither line will ever be fully loaded by line-to-neutral loads.
 
161125-1023 EST

A three wire size change is a 2 times change in resistance. Take a look at resistance tables.

Source impedance for a hot and neutral of equal size is 2*R, and for a neutral of 1 0 and a hot of 4 0 (a three wire size change) the source impedance is (1+2)*R = 3 R a 50% increase. Does it matter, possibly in greater light flicker.

Personally I want a low impedance to my main panel. From there it is under my control.

.
 
Smart $ said:
George's reply isn't all that obvious in intent, especially with your being from across-the-pond and all. What it means that residential services typically have enough line-to-line load that neither line will ever be fully loaded by line-to-neutral loads.
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I gave a "what if" scenario. My geographical locatiion has nothing to do with that.
 
Besoeker said:
I gave a "what if" scenario. My geographical locatiion has nothing to do with that.
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I know. It's just that George brought up "electric dryers, ranges and A/Cs". These are line-to-line (240V) loads here, and I was of the impression that in your corner of the world, your residential service is single voltage... and it may not dawn on you that the loads mentioned contribute very little if any to neutral current... and having any of these loads connected will eliminate the possibility of a full-on unbalanced condition that you asked about.
 
Smart $ said:
I know. It's just that George brought up "electric dryers, ranges and A/Cs". These are line-to-line (240V) loads here, and I was of the impression that in your corner of the world, your residential service is single voltage... and it may not dawn on you that the loads mentioned contribute very little if any to neutral current... and having any of these loads connected will eliminate the possibility of a full-on unbalanced condition that you asked about.
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I was aware of the 240V domestic appliances. My sweet wife is a Southern Belle in case you had forgotten.
 
Besoeker said:
Avoided might better describe it.
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Okay. Let's try again...

Besoeker said:
What if one of the 4/0 conductors loaded to its full rated current capacity and the other not at all?
Then the neutral would have to carry all the current of the loaded 4/0 wouldn't it?
Click to expand...
That's really just one question and the answer is yes.

The sidebar is, if this service supplies any 240V load, neither of the 4/0 conductors could be loaded to its current capacity with 120V loads... in a compliant installation, that is.
 
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 ??

...
Click to expand...

I just want to point out that the way this OP was phrased, to me, implies somewhat unsound reasoning. The service neutral could theoretically carry as many amps as either of the ungrounded conductors if the load is somehow entirely unbalanced, i.e. all on one of those ungrounded conductors. And I don't believe there is anything special about the 1/2 number; if that number is thought to come from 120/240 that is a false understanding.

I saw a house once where some not-very-bright person put all the branch breakers on one busbar. (The panel was literally half full). Not sure why they did that, but I wouldn't tell that person that the service neutral could be smaller until they demonstrated some improved understanding in other areas. :happyno:
 
jaggedben said:
I just want to point out that the way this OP was phrased, to me, implies somewhat unsound reasoning. The service neutral could theoretically carry as many amps as either of the ungrounded conductors if the load is somehow entirely unbalanced
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Thank you. That was my point.
 
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