Why full size neutral single phase?

[mivey]

You are not making any sense here.

My statement was that if you reduce branch circuit current the neutral current will decrease.

You say that is false, please elaborate.

Actually struck me as quite funny when you put it like that. Given how smart Besoeker is it struck me as funny picturing him saying something like that, which he does not support but seemed to just by what he wrote.

 

[mbrooke]

I have upgraded services on some of those when they added AC.

Same here, but most of those same schools now have AC in at least portions of the buildings, though most are seeing AC nearly everywhere.

The small school districts around here share a school nurse. They only are there long enough to perform some basic physical exams once a year on each student, and the room they use for that is vacant most of the time otherwise. If a child gets sick or injured during school a teacher or other staff may stay with that child until parent arrives to pick them up, unless it is something serious enough then an ambulance may be called, and parent is directed to meet them at hospital. Many small schools do have someone that is a volunteer EMT on their staff, not that they seek them out, it just happens that way in small towns.

The schools I went to had a full time nurse on deck, so I guess it really does vary by location.

 

[kwired]

The schools I went to had a full time nurse on deck, so I guess it really does vary by location.

When I was in school there was a nurse there, maybe not full time but quite often. But that wasn't exactly yesterday. Today at the schools in this region you will almost never see one. Maybe different in bigger towns/cities but not in the little schools in these towns with less then 1500 population. They come in only once or twice a year and check vision, hearing, and other basic physical examinations of students, and are seldom ever seen otherwise.

 

[iwire]

The third harmonic content from each phase in a three phase system adds in the neutral. That's what happened.

Yes it does, something I have known for a fair time now and have not disputed on any forum.

However you claim I said something untrue. We can leave it at that if you would like.

 

[Besoeker]

You are not making any sense here.

My statement was that if you reduce branch circuit current the neutral current will decrease.

You say that is false, please elaborate.

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.

 

[Besoeker]

Actually struck me as quite funny when you put it like that. Given how smart Besoeker is it struck me as funny picturing him saying something like that, which he does not support but seemed to just by what he wrote.

I gave a response to mbrooke's point.
A specific, real life example. Whether I said it or not doesn't change that.

 

[mivey]

I gave a response to mbrooke's point.
A specific, real life example. Whether I said it or not doesn't change that.

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.

 

[Besoeker]

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.

Life moves on.
One of my grand daughters jumped on a bench, sang, and jumped down. Straight on to my dog, Max.
He was fine - moved a couple of feet. She was distraught.

Is there a point?

Not a lot. Just that we have different perspectives on things.

 

[GoldDigger]

Suppose you have a load which is 75% third harmonic.
Load each phase to only 50%.
Third harmonic per line is then 37.5%.
Total neutral current is then 112%.
Note that neutral current is then over 100% for a full sized neutral and the line current is not "in the upper end".

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[Cletis]

Wow, i didnt realize reducing a nuetral thread could be so entertaining


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[mivey]

Suppose you have a load which is 75% third harmonic.
Load each phase to only 50%.
Third harmonic per line is then 37.5%.
Total neutral current is then 112%.
Note that neutral current is then over 100% for a full sized neutral and the line current is not "in the upper end".

Sent from my XT1585 using Tapatalk

Suppose you have a load which is 99% 3rd harmonic and 34% load on each phase then the neutral is still over 100% loaded.

 

[ptonsparky]

Wow, i didnt realize reducing a nuetral thread could be so entertaining


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You never know what or whose trigger you'll trip. Better than daytime TV that is or sure.

 

[mivey]

Suppose we have a case where the conductor was undersized so bad that the neutral is loaded past its ampacity when used. Then the neutral would be overloaded. Just sayin'.

 

[Fulthrotl]

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

.
we don't have that here. we are talking the difference between 2/0 and 1/0 aluminum,
in a single service riser. i was generous calling it at 20'. under $3 direct costs.

i do service changes at $2,200. i use copper, and i don't derate
the neutral, and it's about a $1,500 day clear, subtracting
materials and fixed operating costs for the day, and wasting
all that money on copper wire. and i will hit base hits like that
every day they get pitched to me. 4 of them a week, 50 weeks
a year is $300k net taxable, just ripping out cans.

seeing as we are picking flypoop out of pepper, and leaving
my two worthless posts out of the count, we now have a
delta of $2.80, divided by 113 posts. your posts have now
changed from a value of $0.0538 to $0.0247787611.

that's my two cents worth.

 

[peter d]

.
we don't have that here. we are talking the difference between 2/0 and 1/0 aluminum,
in a single service riser. i was generous calling it at 20'. under $3 direct costs.

i do service changes at $2,200. i use copper, and i don't derate
the neutral, and it's about a $1,500 day clear, subtracting
materials and fixed operating costs for the day, and wasting
all that money on copper wire. and i will hit base hits like that
every day they get pitched to me. 4 of them a week, 50 weeks
a year is $300k net taxable, just ripping out cans.

seeing as we are picking flypoop out of pepper, and leaving
my two worthless posts out of the count, we now have a
delta of $2.80, divided by 113 posts. your posts have now
changed from a value of $0.0538 to $0.0247787611.

that's my two cents worth.

We use aluminum for services. Anyone who uses copper for a residential service around here probably stole it off the job trailer during their day job.

 

[mbrooke]

Suppose you have a load which is 75% third harmonic.
Load each phase to only 50%.
Third harmonic per line is then 37.5%.
Total neutral current is then 112%.
Note that neutral current is then over 100% for a full sized neutral and the line current is not "in the upper end".

Sent from my XT1585 using Tapatalk

And when #12 good for technically 30amps, restricted to 20, and an 80% rule for lighting circuits; 112% doesnt even push that noodle over 20amps continuous. Now, BS7671: 114% x 30 = 33.6 amps. Harmonics here now make a difference.

 

[mbrooke]

BTW, you know how forum members here created a phase/neutral current Xcel sheet? Can someone do the same factoring harmonics :angel:

 

[ptonsparky]

BTW, you know how forum members here created a phase/neutral current Xcel sheet? Can someone do the same factoring harmonics :angel:

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.

 

[peter d]

Id argue that still holds true outside of the nurse's office.

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.

 

[JFletcher]

.
we don't have that here. we are talking the difference between 2/0 and 1/0 aluminum,
in a single service riser. i was generous calling it at 20'. under $3 direct costs.

i do service changes at $2,200. i use copper, and i don't derate
the neutral, and it's about a $1,500 day clear, subtracting
materials and fixed operating costs for the day, and wasting
all that money on copper wire. and i will hit base hits like that
every day they get pitched to me. 4 of them a week, 50 weeks
a year is $300k net taxable, just ripping out cans.

seeing as we are picking flypoop out of pepper, and leaving
my two worthless posts out of the count, we now have a
delta of $2.80, divided by 113 posts. your posts have now
changed from a value of $0.0538 to $0.0247787611.

that's my two cents worth.

"Here's my ten cents; my two cents is free
A nuisance, who sent, you sent for me?"