4000 amp 480v 3ph switch gear

[wwhitney]

it is my opinion that 300.3(B)(3) permits the use of isolated phase installations anywhere you want to use them. There is no need for the exception to 300.3(B)(1).

+1

That's the only logical conclusion under Charlie's Rule.

Cheers, Wayne

 

[roger]

The NEC does not prohibit isophase installations.

Point out one post where someone said it was prohibited by the NEC.

They embrace them

The NEC doesn't embrace the method it simply allows it and there are rules that must be adhered to before using the method.

There is nothing to be afraid of in promoting this. Incumbency does carry clout which is why you see the 5% number being used as the lever.

Actually the OP's scenario and your post # 9 are examples of why it can't be used per the NEC rules, so add this to the reasons.

Roger

 

[dionysius]

That is incorrect.:happyno:


Here is the code section from 2014 NEC




The only NEC permitted isophase installations are described in the exception above.

Therefore isophase installations cannot be used for any circuit above ground or in a metal raceway or cable. The eliminates most applications of isophase.

Thank you for pointing out that I failed to constrain my statements for the bigger audience. Mea maxima culpa. I am man enough to admit when I am wrong since I am here to learn and extend the art and craft. I must say that there is at least one character on this forum who not only refuses to admit his mis-statements but actually enters into ad hominem attacks whenever his errors are pointed out. It is good that he is the exception.

I was considering only the beautiful picture of the isophase UG PVC conduit installation that you had published below which was my failure in not making that crystal clear.

The very interesting point to me is that the code aficionados made such an exception to include this special case since practically all new major service installations are UG in PVC like you had depicted. Note.....there is no extra derating required for this exception above non isophasing as was stated by many here who are uncomfortable with the stretch. I would like to see them recant on that.

Here is that fine pic once again that has to be admired both aesthetically and technically........

 

[Ingenieur]

Thank you for pointing out that I failed to constrain my statements for the bigger audience. Mea maxima culpa. I am man enough to admit when I am wrong since I am here to learn and extend the art and craft. I must say that there is at least one character on this forum who not only refuses to admit his mis-statements but actually enters into ad hominem attacks whenever his errors are pointed out. It is good that he is the exception.

taking the high road and actually walking it, and giving the impression you are by patting yourself on the back are two different things
one is genuine, the other disingenuous
you claim the high road, then attack someone back-handedly
you are doing what you condemn and accuse others of doing...what's that called?

point out their 'mis-statements' please
there is a reason it is a minute percentage of all installations and seldom the first or de facto choice

 

[dionysius]

there is a reason it is a minute percentage of all installations and seldom the first or de facto choice

The only point I am making is that within the context of new UG PVC encased service installations the isophasing approach should be considered every time as a preferred solution. The absence of proximate metallic material is the key factor to watch out for so no induced currents can cause heating or parasitic loading. The reciprocating piston engine shows us the power of incumbency. After massive billions of R&D over 100+ years in is the standard but from an engineering and physics viewpoint it is a lackluster offering. A little off topic......sorry but germane to a point I made before re isophasing.

 

[Ingenieur]

The only point I am making is that within the context of new UG PVC encased service installations the isophasing approach should be considered every time as a preferred solution. The absence of proximate metallic material is the key factor to watch out for so no induced currents can cause heating or parasitic loading. The reciprocating piston engine shows us the power of incumbency. After massive billions of R&D over 100+ years in is the standard but from an engineering and physics viewpoint it is a lackluster offering. A little off topic......sorry but germane to a point I made before re isophasing.

even if conduit count/size and conductor count/size are the same for both it is likely the complexity of termination will also be similar
so use the balanced abc approach and take advantage of the inherent field cancelling

but in most cases the conduits/conductors required will be greater for the isophase

again, there is a reason you see very few isophase installs, even when it gives a cleaner termination geometry
either because it is cheaper or there is no advantage
Like I and others have said, a few out of hundreds

 

[wwhitney]

even if conduit count/size and conductor count/size are the same for both it is likely the complexity of termination will also be similar

Disagree. The whole point of isophase is the greater ease of termination while maintaining equal conductor lengths within parallel sets.

Cheers, Wayne

 

[dionysius]

Disagree. The whole point of isophase is the greater ease of termination while maintaining equal conductor lengths within parallel sets.

Cheers, Wayne

Exactly the point I keep making over and over again.

Isophase promotes a significant labor savings; all conductors can be precut to same length precisely; radii of curvature can be identical; if precolored cabling is used then none of this marking is needed; a time and motion study would make for a fraction of the install time. The people on here are very smart and experienced but changing minds takes a lot of effort. What is it about the human that seems to make them dig in.

 

[roger]

Exactly the point I keep making over and over again.

Isophase promotes a significant labor savings; all conductors can be precut to same length precisely; radii of curvature can be identical; if precolored cabling is used then none of this marking is needed; a time and motion study would make for a fraction of the install time. The people on here are very smart and experienced but changing minds takes a lot of effort. What is it about the human that seems to make them dig in.

What you're missing is, as others have pointed out to you there are few instances where isophase installations can be used and the OP's scenario and your posts following the OP cannot be done code compliant so they cannot be part of your argument for promoting it.

Then there is where you made the statement

there is no extra derating required for this exception above non isophasing as was stated by many here who are uncomfortable with the stretch. I would like to see them recant on that.

They are correct, in Iwires picture the conductors would have to be derated to 80% since there are four CCC's in each conduit, see Table 310.15(B)(3)(a). A non-Isophase installation would most likely be considered three CCC's and not need any derating at all so there is no recanting necessary.

Roger

 

[dionysius]

What you're missing is, as others have pointed out to you there are few instances where isophase installations can be used and the OP's scenario and your posts following the OP cannot be done code compliant so they cannot be part of your argument for promoting it.

Then there is where you made the statement They are correct, in Iwires picture the conductors would have to be derated to 80% since there are four CCC's in each conduit, see Table 310.15(B)(3)(a). A non-Isophase installation would most likely be considered three CCC's and not need any derating at all so there is no recanting necessary.

Roger

I am only talking of UG PVC clad installs.

His picture is that of a service or at least that is what is most likely. It is a large trafo to a switchboard. Looks like an industrial 480Y/277 service from a 2 or 3 thousand kVA transformer. No derating required on those service feeders.

 

[roger]

I am only talking of UG PVC clad installs.

So, we are all talking about that

His picture is that of a service or at least that is what is most likely. It is a large trafo to a switchboard. Looks like an industrial 480Y/277 service from a 2 or 3 thousand kVA transformer.

So, that changes nothing.

No derating required on those service feeders.

Without any babble, point us the NEC section that states that.

You almost appear to be trolling, so how about coming forward with substantiation to your statements or just admit you are off base in the conversation.

Roger

 

[dionysius]

You almost appear to be trolling, so how about coming forward with substantiation to your statements or just admit you are off base in the conversation.

Roger

I have neither the time nor the inclination to troll, Roger.

I was posting re contrast/comparison of iso vs. non-iso which I can understand if you missed that in my words. Derating was used to "sell" the non-iso only pitch. Not fair.

I want to be fair to all and banish fear. I have detected that at least some of the resistance to iso is because of the embedded "we always done it that way" thinking. Please page back to read my write up on the analysis of formulae for mutual inductance that I submitted to this thread. Give me your comments on same.

I would like to think that an Inspector will give due diligence to an iso installation if /when he/she encounters one.

I have no other dog in the fight.

 

[roger]

I have neither the time nor the inclination to troll, Roger.

Thanks

I was posting re contrast/comparison of iso vs. non-iso which I can understand if you missed that in my words. Derating was used to "sell" the non-iso only pitch. Not fair.

No, derating was brought to the table with the NEC article section requiring it, quite fair and relevant.

I want to be fair to all and banish fear. I have detected that at least some of the resistance to iso is because of the embedded "we always done it that way" thinking.

I haven't seen that, I have seen most of the others in the discussion provide NEC reasons for their back up.

Please page back to read my write up on the analysis of formulae for mutual inductance that I submitted to this thread. Give me your comments on same.

Sorry to say it but that has no bearing in the conversation as far as what the NEC allows.

I would like to think that an Inspector will give due diligence to an iso installation if /when he/she encounters one.

IOW's, you are hoping an inspector would ignore the code they are supposed to enforce

I have no other dog in the fight.

Now, do you know why the OP's two options and your follow up can not be done per the NEC?

Roger

 

[Ingenieur]

Disagree. The whole point of isophase is the greater ease of termination while maintaining equal conductor lengths within parallel sets.

Cheers, Wayne

if you have 9 conduit each with 3 conductors the complexity will be similar
a lot is determined by the termination lugs
what may be better on one end may be messier on the other
even if it saves an hour or 2 in a project that involves a pad, xfmr, duct bank, switchgear, etc
every installation I have seen was/is still done conventionally

there is a reason why you very rarely see it
1000's of electricians can't all be wrong lol

 

[Ingenieur]

I have neither the time nor the inclination to troll, Roger.

I was posting re contrast/comparison of iso vs. non-iso which I can understand if you missed that in my words. Derating was used to "sell" the non-iso only pitch. Not fair.

I want to be fair to all and banish fear. I have detected that at least some of the resistance to iso is because of the embedded "we always done it that way" thinking. Please page back to read my write up on the analysis of formulae for mutual inductance that I submitted to this thread. Give me your comments on same.

I would like to think that an Inspector will give due diligence to an iso installation if /when he/she encounters one.

I have no other dog in the fight.

No one fears anything...nonsense
it was 'always done that way' because it is 'better', cost, ease, conduit/wire size
not to mention code compliance
if isophase was better no one would be afraid to use it to increase profit
if code compliant and there was a buck to be made it would be used
crazy talk

 

[wwhitney]

if you have 9 conduit each with 3 conductors the complexity will be similar

I still disagree.

The 3 lugs will typically be arranged in a line.

With isophase, each lug will have 9 conductors going to just 3 different conduits, and those conduits carry nothing else. You can arrange those conduits so that one is under the lug, the others are neighboring and spread perpendicular to the spread of the lugs. The variation in lug to conduit distance is low, and it is not much trouble to keep the conductors all the same length. The layout of conduits is a separate issue for each lug, no interference.

With mixed phase, each lug will have 9 conductors, 1 going to each of the 9 different conduit. The spread of those 9 conduits will be much greater. Also, at most one lug can be centered over the centroid of the conduit pattern; for the other lugs, the spread of distances from lug to conduit will be quite a bit higher. It will be harder to keep all the conductors the same length.

Cheers Wayne

 

[iwire]

I still disagree.

The 3 lugs will typically be arranged in a line.

With isophase, each lug will have 9 conductors going to just 3 different conduits, and those conduits carry nothing else. You can arrange those conduits so that one is under the lug, the others are neighboring and spread perpendicular to the spread of the lugs. The variation in lug to conduit distance is low, and it is not much trouble to keep the conductors all the same length. The layout of conduits is a separate issue for each lug, no interference.

With mixed phase, each lug will have 9 conductors, 1 going to each of the 9 different conduit. The spread of those 9 conduits will be much greater. Also, at most one lug can be centered over the centroid of the conduit pattern; for the other lugs, the spread of distances from lug to conduit will be quite a bit higher. It will be harder to keep all the conductors the same length.

Cheers Wayne

Wayne, what you can make sound so easy on a forum is not how easy it is in real life

 

[Ingenieur]

I still disagree.

The 3 lugs will typically be arranged in a line.

With isophase, each lug will have 9 conductors going to just 3 different conduits, and those conduits carry nothing else. You can arrange those conduits so that one is under the lug, the others are neighboring and spread perpendicular to the spread of the lugs. The variation in lug to conduit distance is low, and it is not much trouble to keep the conductors all the same length. The layout of conduits is a separate issue for each lug, no interference.

With mixed phase, each lug will have 9 conductors, 1 going to each of the 9 different conduit. The spread of those 9 conduits will be much greater. Also, at most one lug can be centered over the centroid of the conduit pattern; for the other lugs, the spread of distances from lug to conduit will be quite a bit higher. It will be harder to keep all the conductors the same length.

Cheers Wayne

often the lugs are offset/staggered
the pic in this thread could have just as easily (easier?) been done as follows

upsize conductor if required, may not be since it uses 4/conduit = 20% derate
6 sets of 3 with ground
eliminates 2 conduit and 2 pulls and 12 terminations (6 ea end)
and possibly less copper, 1 3 cond run eliminated since no derating is required

orient 2 x 3 duct with center lug along the centerline long axis

 

[wwhitney]

Wayne, what you can make sound so easy on a forum is not how easy it is in real life

Absolutely, I have zero experience doing this kind of install.

But doesn't an isophase installation make it easier to keep the conductors in a parallel set the same length, versus a mixed phase installation?

If not, I don't see the point of isophase at all.

Cheers, Wayne

 

[roger]

But doesn't an isophase installation make it easier to keep the conductors in a parallel set the same length, versus a mixed phase installation?

If not, I don't see the point of isophase at all.

Cheers, Wayne

Wayne, the times I have done it (probably 6 to 8 times in my career) it has indeed made it easier to keep them the same length and made terminating easier overall.

Roger