Why full size neutral single phase?

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peter d said:
Partially, it depends on the age of the building. The middle school I attended (built 1950's, expanded 1967) has some a/c in a few select areas like the band room and science classrooms that was added much later. The other buildings in the district have partial a/c but are all pretty much the same - no a/c in the classrooms.

Now, if you're in a district in a growing area with new buildings, that's a different story entirely.
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I agree, however it varies by each board of ed. I've seen new buildings go up with a broad range of AC options.
 
ptonsparky said:
I was wondering how possible that is. Maybe not so bad if know what the single load characteristics are but mixing them could be fun.

Sounds like a job for others. I have sharp stick that would be more my level of entertainment.
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X2. Id imagine the math would be a bit tricky but you never know. It would certainly put a lot of theories to the test.
 
Besoeker said:
It isn't actually what you stated nor what I claimed you posted was incorrect.
My response was to mbrookes point about reduced neutrals in a three phase system like that used in the UK and that was used in the Burj al Arab.

Harmonics caused the neutral to be overloaded while the line currents were within conductor ratings. A real installation and a real issue.
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NEC does recognize that non linear loads can result in higher heating within neutral conductors of three phase four wire wye circuits. It still mostly leaves it up to the designer how to determine what size of conductor to use is sufficient though.
 
mivey said:
I know. You were talking about one thing and Iwire another. Iwire took it to mean you were saying reducing the total load would not subsequently reduce neutral current. Just struck me as funny this morning.
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Well maybe you can tell me what beo is talking about because he cannot seem to explain it to me. :D
 
Besoeker said:
Harmonics caused the neutral to be overloaded while the line currents were within conductor ratings. A real installation and a real issue.
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No kidding, you keep saying that and I keep not disputing it. :D

But there is more than one way to keep the neutral from being overloaded.

One way is to make the neutral larger than the line conductors.

Another way is to use all the same standard size conductors but not load them as heavily.

Run more circuits, not larger conductors. In my opinion that is a better design, to each their own.
 
iwire said:
No kidding, you keep saying that and I keep not disputing it. :D

But there is more than one way to keep the neutral from being overloaded.

One way is to make the neutral larger than the line conductors.
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Surely you don't mean more than full sized!!!!!!
 
Besoeker said:
Surely you don't mean more than full sized!!!!!!
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If even-numbered harmonics are significant, you might have to have an oversized neutral for split phase. Similarly, if multiple-of-3 harmonics are significant, which is usually more common, you'd have to do the same for 3-phase. These harmonics add up on the neutral, rather than cancel.


For purly linear loads, there is no need for an oversized neutral.
 
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