# Neutral size



## stedan (Jun 23, 2010)

what size neutral on a 400 amp service? This application is in a building for a utility company and the prints show parallel 4/0 feeds and a single 2/0 neutral


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## oldtimer (Jun 10, 2010)

stedan said:


> what size neutral on a 400 amp service? This application is in a building for a utility company and the prints show parallel 4/0 feeds and a single 2/0 neutral


 If this is a parallel service, and the feeds are parallel 4/0. I M O, the neutral should also be parallel 2/0. Please correct me if I am wrong. :icon_smile:


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## Bob Badger (Apr 19, 2009)

stedan said:


> what size neutral on a 400 amp service? This application is in a building for a utility company and the prints show parallel 4/0 feeds and a single 2/0 neutral


It cannot be smaller than the EGC for that size circuit and it has to be able to carry the calculated imbalance of the feeder.

See 2008 220.61


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## Bob Badger (Apr 19, 2009)

oldtimer said:


> If this is a parallel service, and the feeds are parallel 4/0. I M O, the neutral should also be parallel 2/0. Please correct me if I am wrong. :icon_smile:


If they are run in separate conduits that is correct.

If they are all in the same conduit a single 2/0 could be permitted.


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## stedan (Jun 23, 2010)

how do you determine the neutral size? and is there a chart in the code book for sizing the neutrals?


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## Bob Badger (Apr 19, 2009)

stedan said:


> how do you determine the neutral size? and is there a chart in the code book for sizing the neutrals?


No chart, it has to be full size or you can do the calculations described in the code section I posted.


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## Bob Badger (Apr 19, 2009)

The reason there is no chart is because it is always different.

1)If you have a 400 amp service that only supplies line to line loads you could reduce the neutral to the size of the EGC.

2)If you have a 400 amp service that only supplies line to neutral loads the neutral will have to be full size.

3)If you have a 400 amp service that supplies both L to L and L to N loads the size of the neutral can be reduced to only have to carry the greatest possible current on the neutral.

There is no way to go with #3 without load calculations.


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## NolaTigaBait (Oct 19, 2008)

What about #4?...Go down 2 sizes and you are good:jester:


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## Bob Badger (Apr 19, 2009)

NolaTigaBait said:


> What about #4?...Go down 2 sizes and you are good:jester:


Truthfully that is not covered by the NEC, you would have to do the calculations to see if 'two sizes' down works ........ it will in most homes but may not work for commercial services.


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## NolaTigaBait (Oct 19, 2008)

Bob Badger said:


> Truthfully that is not covered by the NEC, you would have to do the calculations to see if 'two sizes' down works ........ it will in most homes but may not work for commercial services.


I know...I was f'n around.


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## Bob Badger (Apr 19, 2009)

NolaTigaBait said:


> I know...I was f'n around.



Oh.


I did not know the NEC was used in NOLA. :whistling2::laughing:


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## NolaTigaBait (Oct 19, 2008)

Bob Badger said:


> Oh.
> 
> 
> I did not know the NEC was used in NOLA. :whistling2::laughing:


It's really not....I'm being serious.


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## B4T (Feb 10, 2009)

Bob Badger said:


> Truthfully that is not covered by the NEC, you would have to do the calculations to see if 'two sizes' down works ........ it will in most homes but may not work for commercial services.


 
There used to be a note in 310-16 about reducing the neutral (2) sizes for residential services or am I sniffin too much vapors out of the Scotchkote can :laughing:


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## Dennis Alwon (May 9, 2009)

Black4Truck said:


> There used to be a note in 310-16 about reducing the neutral (2) sizes for residential services or am I sniffin too much vapors out of the Scotchkote can :laughing:


I think you are sniffing too much something. :laughing:


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## Shorty Circuit (Jun 26, 2010)

Bob Badger said:


> It cannot be smaller than the EGC for that size circuit and it has to be able to carry the calculated imbalance of the feeder.
> 
> See 2008 220.61


What if the imbalance is 100% and there is only load on one phase leg? Then the neutral would have to carry the same load as the one phase and its OCPD is 400 amps.

"No chart, it has to be full size or you can do the calculations described in the code section I posted."

IMO full size is a good choice and the one I use for Y connected transformers. However, even full neutrals can burn up due to harmonics which don't cancel. That's why you can buy panels with double sized neutrals and why high K rated transformers have larger neutrals too. Between harmonics from SMPSs and worrying about open neutrals I stopped specifying multiwire branch circuits nearly 30 years ago and when I started getting reports of guys getting hit on neutrals on lighting circuits with electronic ballasts about 25 years ago due to harmonics developing a voltage over ground at the J box for the home run I stopped using multiwire branch circuits for 277 too.

__________________________________________________________

If it wasn't for bad luck I wouldn't have any luck at all.


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## goose134 (Nov 12, 2007)

Yet another interesting difference in Chicago code. Any service up through 400 amp must have the neutral the same size as phase conductors.


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## Shorty Circuit (Jun 26, 2010)

goose134 said:


> Yet another interesting difference in Chicago code. Any service up through 400 amp must have the neutral the same size as phase conductors.


Maybe Chicago's worried about another fire. Once burned, twice warned.:devil2::furious::devil:


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> What if the imbalance is 100% and there is only load on one phase leg? Then the neutral would have to carry the same load as the one phase and its OCPD is 400 amps.


Yes and if that is a possibility the NEC requires you have a neutral big enough to handle it.

But if you have a main panel that is loaded with line to line loads you can safely and code compliantly reduce the neutral size. 



iwire said:


> "No chart, it has to be full size or you can do the calculations described in the code section I posted."





shorty said:


> IMO full size is a good choice and the one I use for Y connected transformers.



That is fine as long as the question is how would _you_ like it done but I understood the question to be more of how it can be done question. 



> However, even full neutrals can burn up due to harmonics which don't cancel.


Can in theory but rarely in reality unless the design of the electrical system is entirely poor to start with.




> That's why you can buy panels with double sized neutrals and why high K rated transformers have larger neutrals too.



I have installed many 'Ks' and many 'super neutrals' almost all the documentation that claim these steps are needed come from companies or organizations that stand to make more money from the fear of harmonic currents.




> Between harmonics from SMPSs and worrying about open neutrals I stopped specifying multiwire branch circuits nearly 30 years ago


I think that is short sighted and just CYA specifying.



> and when I started getting reports of guys getting hit on neutrals on lighting circuits with electronic ballasts about 25 years ago due to harmonics developing a voltage over ground at the J box for the home run I stopped using multiwire branch circuits for 277 too.


I will ask you to expand on that part as I am not following you, even a two wire circuit will exhibit voltage drop on the neutral raising it's potential above 'ground'.

__________________________________________________________

If it wasn't for bad luck I wouldn't have any luck at all.[/QUOTE]


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## Shorty Circuit (Jun 26, 2010)

Badger Distinction;

"I will ask you to expand on that part as I am not following you, even a two wire circuit will exhibit voltage drop on the neutral raising it's potential above 'ground'."

The calculated impedence to ground based on the tables is actually usually calculated as the dc resistance. Between impedence increasing due to skin effect and inductance in ferrous couduit as frequency rises, so does voltage drop across it. Therefore at the J-box where the branch circuit neutrals splice to the home run neutral a voltage can develop well above ground due to that impedence which is where you get hit. Now let's say you turn off a breaker on a 277V lighting circuit to add more fixtures. In a multiwire branch circuit, there will be neutral current flowing in the neutral from fixtures still lit on the other two circuits. That's where the voltage appears from and why they get hit, because the voltage at the J box can be well above ground potential at the higher frequencies of the harmonics at that point. 

You get a lot of respect for harmonics when you see a non K-rated transformer with almost no load on it and it's so hot you can't even touch it. You measure the current, you test it, you replace it with a larger one that's also not K rated and it still gets pretty hot. In my first experience with it, it was due mostly to a photocopy machine. Each time it made a copy, the current would jump wildly and the breaker didn't trip. It never crossed the breaker's I/T curve, at least not at the frequency of the harmonics. BTW, I replaced a 75 with a 112.5.

The effect of the ferrous conduit raising impedence as a function of frequency is why if a transformer ground wire is in EMT or rigid you put a bonding jumper between the wire and the conduit at one end, the conduit becomes part of the circuit (better at both ends). I usually run mine in pvc up to the ceiling and then bare. It is also why we ran 400 hz circuits from motor alternators and UPSs to mainframe CPUs in aluminum conduit.

Another problem with any multiwire branch circuit is that an open netural will cause the voltages to divide according to the equivalent parallel resistances of the loads on each phase winding in series with the equivalent parallel resistances of the other phase windings across the phase to phase voltage. For example, in a sigle phase circuit where the neutral opens and there are say several units of load on one leg and only one on the other, most of the voltage will appear across the single load. So say it is 240 volts, then you could see 150 even 175 volts across the single load which will often destroy it. That is how those Saturday afternoon handyman types blow up people's appliances. 

BTW, on a three phase circuit, it's also very bad news if one of the legs on the primary delta side ever opens up. I had that once when I lost one leg on an outdoor transformer due to tracking. There were some pretty high voltages on one or two phases on the secondary side. We shut the builidng down though so we didn't lose anything. Luckily it was on a Friday so they only lost a few hours of work.


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> The calculated impedence to ground based on the tables is actually usually calculated as the dc resistance. Between impedence increasing due to skin effect and inductance in ferrous couduit as frequency rises, so does voltage drop across it. Therefore at the J-box where the branch circuit neutrals splice to the home run neutral a voltage can develop well above ground due to that impedence which is where you get hit. Now let's say you turn off a breaker on a 277V lighting circuit to add more fixtures. In a multiwire branch circuit, there will be neutral current flowing in the neutral from fixtures still lit on the other two circuits. That's where the voltage appears from and why they get hit, because the voltage at the J box can be well above ground potential at the higher frequencies of the harmonics at that point.


I am not believing you.

Harmonics have little to do with the current that hurts us if we work on the neutral of MWBC with only one leg or phase shut down.

Can you point to any outside source that confirms people are getting shocks due to harmonic currents?



> You get a lot of respect for harmonics when you see a non K-rated transformer with almost no load on it and it's so hot you can't even touch it.


We are humans, we are very sensitive to heat, what was the rated temp rise of the unit and was it being exceeded?





> The effect of the ferrous conduit raising impedence as a function of frequency is why if a transformer ground wire is in EMT or rigid you put a bonding jumper between the wire and the conduit at one end, the conduit becomes part of the circuit (better at both ends). I usually run mine in pvc up to the ceiling and then bare. It is also why we ran 400 hz circuits from motor alternators and UPSs to mainframe CPUs in aluminum conduit.


Man you are just jumping all over the place, we were not discussing 400 hz systems and the required bonding at each end of the GEC conduit is not required due to harmonics in 60 hz systems



> Another problem with any multiwire branch circuit is that an open netural will cause the voltages to divide according to the equivalent parallel resistances of the loads on each phase winding in series with the equivalent parallel resistances of the other phase windings across the phase to phase voltage.


No chit, that is a problem with any service or feeder as well, the solution is not to be afraid but to make the connections correctly and professionally. 





> For example, in a single phase circuit where the neutral opens and there are say several units of load on one leg and only one on the other, most of the voltage will appear across the single load. So say it is 240 volts, then you could see 150 even 175 volts across the single load which will often destroy it.


Yes, most of us understand basic electrical theory. 




> That is how those Saturday afternoon handyman types blow up people's appliances.


How many engineered jobs are wired by Saturday morning handymen?






> BTW, on a three phase circuit, it's also very bad news if one of the legs on the primary delta side ever opens up. I had that once when I lost one leg on an outdoor transformer due to tracking. There were some pretty high voltages on one or two phases on the secondary side. We shut the builidng down though so we didn't lose anything. Luckily it was on a Friday so they only lost a few hours of work.


Yes when things break other things can be destroyed, nothing to do with harmonics though.

Here is the thing, we have a member here 'Brian John' he has spent about 30 years working in all sorts of data centers doing PQ testing and as I remember it the only buildings that had damaging levels of harmonic currents where buildings that had never been intended to be used as data centers so the entire electrical infrastructure was under designed.

I know harmonic currents exist, I am not trying to say they do not. All I am saying is much of the hype about them are coming from sources like 'copper.org' that have a direct financial incentive to build up the fear.

If I was designing a data center I would use all two wire circuits, if I was designing almost any other type of occupancy I would use MWBCs as much as possible, they are both electrically efficient and raw material efficient.


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## Shorty Circuit (Jun 26, 2010)

"I am not believing you.

Harmonics have little to do with the current that hurts us if we work on the neutral of MWBC with only one leg or phase shut down.

Can you point to any outside source that confirms people are getting shocks due to harmonic currents?"

No, I got the complaints directly from my electricians. How do you explain it then? If the impedence to ground were low then the voltage at the J-box to the home run should be at or near zero. But it isn't. At least not at some frequencies. Why doesn't that happen with non harmonic loads too? 

"We are humans, we are very sensitive to heat, what was the rated temp rise of the unit and was it being exceeded?"

It's been a long time but I think it was a 75 degree C rise rated unit. We thermoscanned it. It was hot. It's been a long time since, probably around 25 years ago but as I recall it was about 40 or 50 amps per phase on the secondary of a 75KVA. That's not a lot. At first I suspected the transformer might be defective but a 112.5 replacement also ran hot although not nearly as hot. I had someone run the photocopy machine while I watched the meter. Every time the machine made a copy the needle swung all the way to the right. You'd think something might be wrong with the photocopier but it worked perfectly and it never tripped the breaker which was the correct size. 

I've seen a lot of large (and small) companies waste a lot of money on a lot of useless junk, especially things like team building meetings which consumed days of an entire company's productivity. After seeing that I rarely if ever worry about first cost. My jobs are always the most expensive in the short run...and as a whole the cheapest in the long run. For every twenty 42 pole panels I put in, there only has to be one where I couldn't have gotten away with a 30 pole panel instead to pay for the other nineteen. And there is always more than one. I never worry about the cost of wire. And now with NEC being dictated to by ASHRAE and they don't allow you more than a 5% voltage drop from the service entrance to the load, I no longer even have a choice in the matter. I'd rather have a higher voltage drop than risk a MWBC.


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## Shorty Circuit (Jun 26, 2010)

"If I was designing a data center I would use all two wire circuits, if I was designing almost any other type of occupancy I would use MWBCs as much as possible, they are both electrically efficient and raw material efficient."

The main convenience outlet electrical load in most offices now are PCs, printers, fax machines, photocopy machines with the same high harmonic generating SMPSs as the file servers and other IT equipment in data centers. According to "The Green Data Center" which I think you can download from the Uptime Institute's Web Site, many of these power supplies are not very efficient. They probably generate far more harmonics than their usable power to their internal load would suggest. It's the same harmonics problem with electronic ballasts. It seems to me that there is not much extra cost to putting seven wires in a conduit instead of five. It's an expense I've judged a good investment and insurance policy in my designs.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> You get a lot of respect for harmonics when you see a non K-rated transformer with almost no load on it and it's so hot you can't even touch it. You measure the current, you test it, you replace it with a larger one that's also not K rated and it still gets pretty hot. In my first experience with it, it was due mostly to a photocopy machine. Each time it made a copy, the current would jump wildly and the breaker didn't trip. It never crossed the breaker's I/T curve, at least not at the frequency of the harmonics. BTW, I replaced a 75 with a 112.5.


You have me at a loss too. One photocopy machine wouldn't provide enough harmonic load to cause a 75 KVA transformer to run hot to the point it fails.

You'd have to explain how this happened. Did you trend and chart the THD %'s?







> Another problem with any multiwire branch circuit is that an open netural will cause the voltages to divide according to the equivalent parallel resistances of the loads on each phase winding in series with the equivalent parallel resistances of the other phase windings across the phase to phase voltage.


Every 4 wire service is a MWB. When installed correctly, there should be no problems using them.


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## Shorty Circuit (Jun 26, 2010)

"You have me at a loss too. One photocopy machine wouldn't provide enough harmonic load to cause a 75 KVA transformer to run hot to the point it fails."

It didn't fail. It just ran much hotter than seemed reasonable in anyone's experience given the load. That machine was not the only load on the transformer but it seemed to be the one load that caused the most heat to be generated. 

"You'd have to explain how this happened. Did you trend and chart the THD %'s?"

You must be joking. My job was to fix it and keep the facility operational, not analyze it. Supporting 20,000 gross square feet of office space at a major software development facility time was far more valuable than money. Besides, this was 25 years ago. I didn't have the equipment at hand and wasn't about to requisition any. Once I started buying K-13 transformers I never saw the problem again. Today I'm back buying the cheapest ones. Good luck to whoever gets stuck with them. First cost seems to be their number one concern. A very short sighted perspective IMO, I always look at cost over the life of the equipment and then decide what makes sense.


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## frenchelectrican (Mar 15, 2007)

I don't know why but in case someone oversighted this part if you have 120/*208* volt single phase network if you have 400 amp service you have to make sure you use full size netural conductor the same size as phase conductors.

And for any Wye connected three phase service my SOP is make sure the netural is the same size as phase conductor the only time I will let it drop if you have full motor load that about it otherwise naw full size and be doen with it.

Merci,Marc


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## Shorty Circuit (Jun 26, 2010)

"I don't know why but in case someone oversighted this part if you have 120/*208* volt single phase network if you have 400 amp service you have to make sure you use full size netural conductor the same size as phase conductors."

That's right. Even on a three phase service, there is no guarantee that you won't have load mostly or even entirely on one phase at some times. If this happens, anything less than a full size neutral would be undersized. This could happen for example if a two pole (single phase) 208 load overloaded upstream fuses in a fused switch distribution circuit. I'm working on a building with a 120/208 incoming service with Square D boltlock and QMR fuses switches as the existing main service disconnect and main switchboard distribution right now.


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> "I don't know why but in case someone oversighted this part if you have 120/*208* volt single phase network if you have 400 amp service you have to make sure you use full size netural conductor the same size as phase conductors."
> 
> That's right. Even on a three phase service, there is no guarantee that you won't have load mostly or even entirely on one phase at some times.


No that is not correct, you can in fact 'guarantee' that the neutral will not be overloaded.

Again it depends on what you are supplying, if the service has few L to N loads and a lot of L to L loads you can safely and code compliantly reduce the neutral size. It is all calculable and predictable.


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## Bob Badger (Apr 19, 2009)

Bob Badger said:


> "If I was designing a data center I would use all two wire circuits, if I was designing almost any other type of occupancy I would use MWBCs as much as possible, they are both electrically efficient and raw material efficient."





Shorty Circuit said:


> The main convenience outlet electrical load in most offices now are PCs, printers, fax machines, photocopy machines with the same high harmonic generating SMPSs


Very true and again you are not telling me anything I am not already aware of.

But how do you load your circuits when you design?

Do you load each 20 amp circuit to 16 amps?

I did not think so, most of the 'cube farms' we do only have 3 to 6 duplex receptacles on a circuit and only supply one or two PC set ups.

Under those conditions it would be imposable to overload the neutral due to harmonics.





> They probably generate far more harmonics than their usable power to their internal load would suggest. It's the same harmonics problem with electronic ballasts.


And as the EU rules become stricter all these power supplies have to produce less harmonic currents which is the smart way to go about it.

Fix the utilization equipment, do not wire the building to compensate for poor equipment design.




> It seems to me that there is not much extra cost to putting seven wires in a conduit instead of five.


It is not that cut and dry, more derating required, larger conductors needed to compensate for that derating, larger conduits required, more voltage drop etc. 



> It's an expense I've judged a good investment and insurance policy in my designs.


But it is not your money you are spending. :no:


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> You must be joking.


Ummm....no.



> Once I started buying K-13 transformers I never saw the problem again.


 

What problem aren't you seeing anymore?

K rated transformers do not solve any harmonic problems, the harmonic currents still circulate within the windings of the transformer. A zig zag will cancel the triplen currents by design, but a K rated won't.


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## Shorty Circuit (Jun 26, 2010)

"Fix the utilization equipment, do not wire the building to compensate for poor equipment design."

You can't have dealt with many IT people...or scientists. They tell you "this is what I bought, it is your job to power it up and make it work, not to tell me what to buy." And they are right.

"Do you load each 20 amp circuit to 16 amps?

I don't know. I've seen laser jet printers pull down voltage so low on inrush current when they made prints they made the fluorescent task light flicker off and crash the pc if it wasn't on a UPS. I think that's about 95 volts. Usually that's due to voltage drop because the original designer or contractor sized the wire for ampacity only not taking into account the distance from the panelboard to the load and the resulting impedence. As a rule of thumb, for every hundred feet on a 120/208 volt circuit, I increase wire size by one gage. So a 20 amp circuit 150 feet from a panelboard gets wired with number 10, not number 12. 

"I did not think so, most of the 'cube farms' we do only have 3 to 6 duplex receptacles on a circuit and only supply one or two PC set ups."

I have no idea where you've worked. I've seen a lot. For example, at AT&T sometimes I'd see two cubes per circuit. Sometimes I'd see ten cubes on three circuits with all ten cubes having all three circuits. I don't try to outguess statistics. I invariably design for worst case and hope for the best. When it fails, nobody accepts that it was cheap as justification. I can't imagine any office without at least one PC in it today. Sometimes more than one. And a printer.

I'm sure you are aware that in some systems such as Steelcase 9000 they use superneutrals, the neutrals being even larger than the phase wires. Not everyone sees things the same way. I'm not an electrical contractor. I don't bid competitively on the cost of getting jobs done. I invariably have to come in to clean up contractor mistakes, especially underdesign.

"But it is not your money you are spending."

It never is...except when I was building my own house. there are no MWBCs in my house.

"K rated transformers do not solve any harmonic problems, the harmonic currents still circulate within the windings of the transformer. A zig zag will cancel the triplen currents by design, but a K rated won't."

The problem I don't see anymore is overheating transformers with unreasonably low loads compared to their rating. K rated transformers have I think for the most part oversized neutrals designed to handle the higher neutral current. I'm not sure what the other differences in costruction are. Zig-zag transformers only work to eliminate odd harmonics when they are perfectly balanced which is never the case in the real world. They work by phase cancellation, that is the vectors of the harmonics on different phases have to be both at the correct angles and of comparable magnitude. If they aren't there is nothing to cancel the harmonics against. That's why I never buy them.

Insofar as saving marginally on sizing wire and conduit, I rarely give it a second thought. Most of the cost is in labor and the labor for installing more neutrals and larger conduit if necessary for a given circuit as well as the material cost differential is in my opinion insignifigant. As I said above, I'm not a contractor so I don't bid against other contractors who will make those marginal cuts to try to edge out the competition.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> K rated transformers have I think for the most part oversized neutrals designed to handle the higher neutral current.


Not exactly



Shorty Circuit said:


> I'm not sure what the other differences in costruction are.


 
Basically think of this. Imagine a 100 amp load running across a 100 amp rated metal bar. It will get hot and put ff heat. 

Now imagine that 100 amp load running across a 200 amp metal bar. Same load, just the heat is dissipated better. K rated transformers have huge windings. That's a K in a nut shell.





Shorty Circuit said:


> Zig-zag transformers only work to eliminate odd harmonics when they are perfectly balanced which is never the case in the real world.


No.




Shorty Circuit said:


> They work by phase cancellation, that is the vectors of the harmonics on different phases have to be both at the correct angles and of comparable magnitude. If they aren't there is nothing to cancel the harmonics against. That's why I never buy them.


What?




Shorty Circuit said:


> Insofar as saving marginally on sizing wire and conduit, I rarely give it a second thought. Most of the cost is in labor and the labor for installing more neutrals and larger conduit if necessary for a given circuit as well as the material cost differential is in my opinion insignifigant.


I am offically lost by your postings now.


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## Shorty Circuit (Jun 26, 2010)

Dnkldorf said:


> Not exactly
> 
> 
> 
> ...


 
That's what I think I said...except it's only for the Neutral winding. Otherwise you might just as well buy a larger transformer and de-rate it. I don't know if there are differences in the core laminations either. More thinner laminations might also reduce harmonics by reducing the ferromagnetic coupling efficiency between the primary and secondary windings at higher frequencies. I'm not sure. Maybe one day I'll look into it.


"No."

"What?"

"I am offically lost by your postings now"

The Zig-Zag transformer cancels every other harmonic (can't remember if it's odds or evens) by combining them out of phase. But as with 60hz non harmonic loads in a conventional wye winding secondary, it depends on the phase angles of the objectionable part of the waveforms combining correctly which means in amplitude as well as offset angle. This is expressed by a vector diagram.

http://www.scribd.com/doc/30066767/Zig-Zag-Transformers

http://en.wikipedia.org/wiki/Vector_group

The offset phase angles can be chosen arbitrarily so long as they match for the three windings of the same transformer. This allowed a Canadian firm to come up with a novel idea. They build zig-zag transformers to any phase offset angle and recommend that in a multistory building, each story have its own phase offset angle different from the other floors so that there isn't an inadvertent adding of harmonics between floors if the imbalances happens to combine on the same phase at some time. This would risk overloading the neutral on the riser bus.

Don't feel too badly if you don't get it. The chief electrical engineer in the firm I was working at when I last saw it attended the same seminar and sales presentation as I did and he didn't get it either. Zig-zag transformers have been around a long time but they aren't very popular. They are expensive and I have a strong hunch that as I said, in the real world they don't work very well to reduce harmonics much of the time.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> Don't feel too badly if you don't get it. The chief electrical engineer in the firm I was working at when I last saw it attended the same seminar and sales presentation as I did and he didn't get it either. Zig-zag transformers have been around a long time but they aren't very popular. They are expensive and I have a strong hunch that as I said, in the real world they don't work very well to reduce harmonics much of the time.


 
I get it. 

I am not getting how you explain it, nor do I understand the statement that a zig-zag must be perfectly balanced in order to be effective.

Where did you get that from?


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## 10492 (Jan 4, 2010)

One last thing. 

If your so worried about harmonics causing MWBC problems, which they don't, just install all 240/120V 1ph transformers and be done with the worrying.


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## Bob Badger (Apr 19, 2009)

Dnkldorf said:


> If your so worried about harmonics causing MWBC problems, which they don't, just install all 240/120V 1ph transformers and be done with the worrying.


You bet, use three of them so the primary sides can be balanced across the 3 phase feeder.


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## Shorty Circuit (Jun 26, 2010)

Dnkldorf said:


> I get it.
> 
> I am not getting how you explain it, nor do I understand the statement that a zig-zag must be perfectly balanced in order to be effective.
> 
> Where did you get that from?


''

It's the conclusion I came to the first time someone tried to sell me one. Because it works by phase cancellation just the way the 60 hz components cancel on the neutral when a transformer is perfectly balanced.

Why not just use 120-240 volt transformers? Besides being unable to support 208 volt three phase loads, what makes you think that would solve the problem of harmonic currents on the neutral? These switching mode power supplies (SMPSs) switch current on and off at very high speed using high power semiconductors and critical timing circuits. To cancel each other out, they must meet at precisely the right time. At 60 hz, this is locked in by the utility. But in the load each one is a local circuit within the load and they are not coordinated. The higher the harmonic, the more likely they are to miss each other like ships passing in the night. Then they don't cancel and subtract from each other, they add.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> Why not just use 120-240 volt transformers? Besides being unable to support 208 volt three phase loads, what makes you think that would solve the problem of harmonic currents on the neutral?


First, 3 phase loads have nothing to do with harmonics on a nuetral.



Shorty Circuit said:


> These switching mode power supplies (SMPSs) switch current on and off at very high speed using high power semiconductors and critical timing circuits. To cancel each other out, they must meet at precisely the right time. At 60 hz, this is locked in by the utility. But in the load each one is a local circuit within the load and they are not coordinated. The higher the harmonic, the more likely they are to miss each other like ships passing in the night. Then they don't cancel and subtract from each other, they add.


What?

Not in a single phase system 180 degrees out of phase from each other.

Triplens are not present.

Where did you get this information at?


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> ''
> 
> It's the conclusion I came to the first time someone tried to sell me one. Because it works by phase cancellation just the way the 60 hz components cancel on the neutral when a transformer is perfectly balanced.
> 
> Why not just use 120-240 volt transformers? Besides being unable to support 208 volt three phase loads, what makes you think that would solve the problem of harmonic currents on the neutral? These switching mode power supplies (SMPSs) switch current on and off at very high speed using high power semiconductors and critical timing circuits. To cancel each other out, they must meet at precisely the right time. At 60 hz, this is locked in by the utility. But in the load each one is a local circuit within the load and they are not coordinated. The higher the harmonic, the more likely they are to miss each other like ships passing in the night. Then they don't cancel and subtract from each other, they add.



The wheels just came off you're wagon. :laughing::laughing::laughing::laughing:


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## Shorty Circuit (Jun 26, 2010)

So what are you saying, that there will be no harmonics coming back on the neutral of a single phase transformer or that they will cancel each other so in either case I don't have to worry about them? But according to you I don't have to worry about them anyway because the whole thing is bogus and greatly overblown, just a scare to sell more copper.


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## frenchelectrican (Mar 15, 2007)

Will someone pick up the dolt's wire wheel up ?? I think it did flew over to my country { Merde ! } 


Shorty.,,


I never heard shuch a thing on *single phase* haromaic issue at all if you have some kind of doucoments to back it up then show it to our ase !! 

Merci.
Marc


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## Shorty Circuit (Jun 26, 2010)

frenchelectrican said:


> Will someone pick up the dolt's wire wheel up ?? I think it did flew over to my country { Merde ! }
> 
> 
> Shorty.,,
> ...


Don't you think that when you plug a computer into a wall outlet in your home it doesn't generate harmonics the way it does in an office? What about the printer connected to it? What about a light dimmer. As more and more appliances have SMPSs powering computer chips like washers, dryers, refrigerators, you don't think that could eventually become a problem? Instead of constantly looking for documents to read, why don't you try to think for yourself? Anyway, the transformer is the utility's problem, the neutrals on the branch circuits are the homeowners...and yours.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> So what are you saying, that there will be no harmonics coming back on the neutral of a single phase transformer or that they will cancel each other so in either case I don't have to worry about them?


Yup, in a nut shell. 



Shorty Circuit said:


> But according to you I don't have to worry about them anyway because the whole thing is bogus and greatly overblown, just a scare to sell more copper.


Well not quite.

It is overblown by people who don't understand how harmonics are produced, the problems they can cause, and remedies available to deal with them.

It is a little more involved than putting your hand on top of a transformer.


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## frenchelectrican (Mar 15, 2007)

Shorty Circuit said:


> Don't you think that when you plug a computer into a wall outlet in your home it doesn't generate harmonics the way it does in an office? What about the printer connected to it? What about a light dimmer. As more and more appliances have SMPSs powering computer chips like washers, dryers, refrigerators, you don't think that could eventually become a problem? Instead of constantly looking for documents to read, why don't you try to think for yourself? Anyway, the transformer is the utility's problem, the neutrals on the branch circuits are the homeowners...and yours.


 
I just want to make it clear for vous { you } most of the circuits I dealt with it they are straight non MWBC they are not much a issue if designed right and with MWBC single phase circuits that is pretty rare to see harmaonic issue either in USA side or France side due they will cancel it out but three phase MWBC yeah if not carefull it will " bit " ya but done right as other members here explaing to ya.

I don't have to dig up very far on the info due other guys allready lay out the details and their experince and they are pretty much right on the spot.

Oh, speaking of European requirements on Harmoic issue they are somehow more tighter due we run on 50 HZ but it will have simauir result as 60 HZ system is on now.

The whole key issue is you have to know what the plans is and how you deal it in correct way.

Merci.
Marc


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## slickvic277 (Feb 5, 2009)

Back to the original question, For Service Entrance can you use table 250.66 for the grounded conductor sizing? As per 250.24 (c)(1) or am I misinterpreting the article?


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> Don't you think that when you plug a computer into a wall outlet in your home it doesn't generate harmonics the way it does in an office?


No.

There are NO damaging harmonic currents on the neutral of single phase source.

Harmonic currents only build up on the neutral from a 3 phase source.


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## Shorty Circuit (Jun 26, 2010)

Bob Badger said:


> No.
> 
> There are NO damaging harmonic currents on the neutral of single phase source.
> 
> Harmonic currents only build up on the neutral from a 3 phase source.


"However, even full neutrals can burn up due to harmonics which don't cancel. Can in theory but rarely in reality unless the design of the electrical system is entirely poor to start with.



Quote:
That's why you can buy panels with double sized neutrals and why high K rated transformers have larger neutrals too. 

"I have installed many 'Ks' and many 'super neutrals' almost all the documentation that claim these steps are needed come from companies or organizations that stand to make more money from the fear of harmonic currents."

Will the real Bob Badger please stand up. It isn't a problem. It can be a problem. The nice thing about arguing both sides of the same issue is that wherever the truth lies, you will always be on the right side of it. But in the same thread even if on different pages, c'mon.


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## wildleg (Apr 12, 2009)

stop being a troll. If you want to learn about harmonics on power systems go do some reading. if you want to prove that someone is wrong, cite some references. regurgitating your own BS is just an annoyance, at best.


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> "However, even full neutrals can burn up due to harmonics which don't cancel. Can in theory but rarely in reality unless the design of the electrical system is entirely poor to start with.
> 
> 
> 
> ...



If you have a point to make say it, you might also try figuring out how to work the quote button so people know who said what. :laughing:


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## 10492 (Jan 4, 2010)

Bob Badger said:


> If you have a point to make say it, you might also try figuring out how to work the quote button so people know who said what. :laughing:


The harmonics in his home must be screwing with his puter.:whistling2:


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## Shorty Circuit (Jun 26, 2010)

Bob Badger said:


> Man you are just jumping all over the place, we were not discussing 400 hz systems and the required bonding at each end of the GEC conduit is not required due to harmonics in 60 hz systems


I don't suppose it occurred to you that harmonics are higher frequency components of a waveform with a 60 hz fundimental and that understanding how they behave in part can be studied by looking at systems where the fundimental is at a higher frequency.

I also don't suppose the equation v(t) = L di(t)/dt means anything to you. Don't bother looking it up in the NEC code, it isn't there. They have nothing beyond substituting numbers to get the arithmetic solution to an algebraic expression and this isn't that. Anyway, that explains why you get hit by harmoics from electronic ballasts on the neutral at the J-box for the home run.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> Anyway, that explains why you get hit by harmoics from electronic dimming ballasts on the neutral at the J-box for the home run.


 
No it doesn't. Next time shut the power off.


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## Shorty Circuit (Jun 26, 2010)

Dnkldorf said:


> No it doesn't. Next time shut the power off.


They do. Read the whole thread. This has to do with MWBC's where power to only the circuit being worked on is turned off but lights on other circuits sharing the same neutral are still powered up.


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## 10492 (Jan 4, 2010)

Shorty Circuit said:


> They do. Read the whole thread. This has to do with MWBC's where power to only the circuit being worked on is turned off but lights on other circuits sharing the same neutral are still powered up.


 
Priceless......:ban:


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## Bob Badger (Apr 19, 2009)

Shorty Circuit said:


> They do. Read the whole thread. This has to do with MWBC's where power to only the circuit being worked on is turned off but lights on other circuits sharing the same neutral are still powered up.


Shorty steps up to the plate ............ but it's a swing and miss.:laughing:

Then the power to 'the circuit' is not off.

A MWBC is defined in Article 100 as a single circuit.

Furthermore the NEC now requires that there is a common means of disconnecting the MWBC at the panel.


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## Shorty Circuit (Jun 26, 2010)

Bob Badger said:


> Shorty steps up to the plate ............ but it's a swing and miss.:laughing:
> 
> Then the power to 'the circuit' is not off.
> 
> ...


Well whatdya know, after all these decades they got it right too. There may be hope even for you yet. Better idea....don't use them. Maybe in a few more issues of the code from now you won't be allowed to but why wait? :thumbup:


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## B4T (Feb 10, 2009)

Good to see Bob has a new friend.. he has been a little lonely since LGLS left. :whistling2:


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## Shorty Circuit (Jun 26, 2010)

Black4Truck said:


> Good to see Bob has a new friend.. he has been a little lonely since LGLS left. :whistling2:


 
I'm hoping he's a lot smarter than he looks :smartass:


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## tcr (Jul 8, 2010)

oldtimer said:


> If this is a parallel service, and the feeds are parallel 4/0. I M O, the neutral should also be parallel 2/0. Please correct me if I am wrong. :icon_smile:


I can let you know definitely that you are right about parellel neutrals because each ungrounded phase must have a neutral in the same conduit in order to eliminate the possibility of high impedance should a fault current occur in either conduit. Consult the nec code section on parallel ungrounded circuits and follow the links to sizing the grounded neutral per conduit.:thumbsup:


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## Mogie (May 26, 2010)

Black4Truck said:


> There used to be a note in 310-16 about reducing the neutral (2) sizes for residential services or am I sniffin too much vapors out of the Scotchkote can :laughing:


You're not sniffin too much Scotchkote - there was such a provision back in the day. I haven't seen it lately, but had no reason to look.


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## frenchelectrican (Mar 15, 2007)

Mogie said:


> You're not sniffin too much Scotchkote - there was such a provision back in the day. I haven't seen it lately, but had no reason to look.


 
I think it was back in 96 or 99 code verison that when the last time I heard they mention two size downstep but only if you can show the load demand caluations if you can able safetly drop down two size on netural condutor and I use this term very loosely.,

Only if you have majorty of line to line loads then you may able reduce it otherwise if your state or local code disallow it then you are stuck with full sized netural conductor. { check with the POCO regualtions as well }

Merci.
Marc


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## electures (Oct 23, 2008)

Sorry for the late post, but...,

*230.31 Size and Rating.*​ 
*(C) Grounded Conductors. *
The grounded conductor shall not be less than the minimum size required by 250.24(C).​ 

*250.24(C) Grounded Conductor Brought to Service Equipment.*​ 
Where an ac system operating at less than 1000 volts is grounded at any point, the grounded conductor(s) shall be run to each service disconnecting means and shall be connected to each disconnecting means grounded conductor (s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. *The grounded conductor(s) shall be installed **in accordance with 250.24(C)(1) through (C)(3).*​


*(1) Routing and Sizing. *​

This conductor shall be routed with the phase conductors and *shall not be smaller than the required grounding electrode conductor specified in Table 250.66 but shall not be required to be larger than the largest ungrounded service-entrance phase conductor. In addition, for service-entrance phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor **shall not be smaller than 12 **1⁄2 **percent of the area of the largest service-entrance phase conductor*. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.


In summary the grounded service conductor shall be sized for the calculated load but in no case smaller than what is specified in Table 250.66. When the size of the ungrounded service entrance conductors exceed Table 250.66 the grounded service conductor shall be sized at 12 1/2% of the ungrounded service entrance conductor size. Consideration must also be given for parallel conductors.​ 


Table 250.66 serves three purposes;​ 


1. Sizing the GEC.​ 
2. Minimum size grounded service entrance conductor brought to the service.​ 
3. Sizing the main bonding jumper at the service disconnect.​ 






I hope this helps answer your question.​


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## uber stein (Aug 20, 2010)

Shorty Circuit said:


> They do. Read the whole thread. This has to do with MWBC's where power to only the circuit being worked on is turned off but lights on other circuits sharing the same neutral are still powered up.


210.4 Each MWBC shall be provided with a means that will simultaneously disconnect *all ungrounded* conductors at the point where the branch circuit originates. 

So the circuits can be turned off and no current will be on the neutral :whistling2:



Bob Badger said:


> Shorty steps up to the plate ............ but it's a swing and miss.:laughing:
> 
> Then the power to 'the circuit' is not off.
> 
> ...


210.4 A Multiwire circuit shall be permitted to be considered as multiple circuits. 

Could'nt find MWBC in Art. 100 

This is in 2008 NEC


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## Dennis Alwon (May 9, 2009)

uber stein said:


> Could'nt find MWBC in Art. 100
> This is in 2008 NEC


Look under branch circuit, multiwire



> Branch Circuit, Multiwire. *A branch circuit* that consists of two or more ungrounded conductors that have a voltage between them, and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.


Some parts of the code, such as 225.30 last sentence consider a MWBC as a single circuit. By the definition it is called *"A branch circuit"* This means one, IMO


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## uber stein (Aug 20, 2010)

Dennis Alwon said:


> Some parts of the code, such as 225.30 last sentence consider a MWBC as a single circuit. By the definition it is called *"A branch circuit"* This means one, IMO


You are right about *some* parts of the code, but not in all cases, it depends on the usage of the MWBC. Under MWBC 210.4, it's considered multiple circuits.


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## Bob Badger (Apr 19, 2009)

uber stein said:


> You are right about *some* parts of the code, but not in all cases, it depends on the usage of the MWBC. Under MWBC 210.4, it's considered multiple circuits.


It is one circuit that in some parts of the code is allowed to be considered two or three circuits, but it remains a single circuit.


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## Josue (Apr 25, 2010)

nice avatar Bob:thumbsup:


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## Shorty Circuit (Jun 26, 2010)

uber stein said:


> 210.4 Each MWBC shall be provided with a means that will simultaneously disconnect *all ungrounded* conductors at the point where the branch circuit originates.
> 
> So the circuits can be turned off and no current will be on the neutral :whistling2:
> 
> ...


I've seen more lighting panels that used multiwire branch circuits than I can count and I've yet to see even one that put light fixtures on a three pole breaker. In a typical office building, shutting off a 3 pole 20 amp breaker could kill a hundred light fixtures or more when a single pole breaker would only kill around 30. A MWBC IMO is just a plain dumb idea. Even panel and transformer manufacturers accept this as oversized neturals are becoming increasingly common. If you need an oversized netural there, why wouldn't you need one in a home run? There is a marginal savings on wire with considerable added risk. In my specs in the general electrical notes it is called out as not permitted in lighting or receptacle panels. And you do have to set up two more reels of white wire. Tough.


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