Where did you get the 5% number from????
Your required derating and oversized conductor is in comparison/contrast to what?? You need more elaboration here to support your posit.
4000 amp 480v 3ph switch gear
- Thread starter freddy.cage
- Start date
- Status
Where did you get the 5% number from????
Your required derating and oversized conductor is in comparison/contrast to what?? You need more elaboration here to support your posit.
- Location
- Massachusetts
I have been doing this work 35 years or so and have only seen isolated phase installations three times and I installed two of those.
kwired
Electron manager
- Location
- NE Nebraska
If you have more then 3 conductors per raceway then ampacity adjustments do factor in, if you have 10 parallel conductors per phase you have reached the 50% adjustment level - that means much larger conductors are needed, if you can keep it in the 4-6 conductors per phase range you may have a chance at keeping same conductor size or only increasing one size from what you would have with ABCN per raceway.
30 years of experience, 5% is generous, much less actually
read my previous posts
for 8 conductors 30% derate
iirc 20% conduit fill
do your own research, no one owes you an explanation
perhaps you wouldn't make goofy advice like isophase based on 90C ratings lol
with no info what so ever: layout, distance, service or feeder, etc
I have been doing this work 35 years or so and have only seen isolated phase installations three times and I installed two of those.
I, 30 years, perhaps 2 or 3 times, very rare
I've seen 100's of installs
the 430 is 90C not practical
assume 10 per phase so 50% derate isophase
No conductor large enough
assume 12/phase need 667 per cond
I'll let you slip by with 2000's at 665 (lahj may not)
24000 mcm/lf
normal grouping
12 sets 400 mcm 4020 A
4800 mcm/lf
this does not factor conduit sizing
or terminations
2000's are pretty stiff lol
Last edited:
- Location
- Massachusetts
In general you get more current per pound of copper with smaller conductors and copper prices being what they are it is often economical to run more conduits then to deal with derating.
- Location
- Massachusetts
I would probably go with a 24" drain pipe.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Think about it this way: In practice, to run isophase, you pretty much have to be going into a switchboard, panelboards are out. Panelboards go up to about 1200 amps. 30% derate for 4-6 CCC is not so bad so there could be a sweet spot in there for like a small 1000-1200, or even 1600 amp switchboard, or larger with multiple service disconnects with a calculated load in the mid teens....Above 6 CCC and the derate is going to start hurting enough that it probably wont be worth those few minutes of gazing at the super neat organized conductors before putting the covers on
Lol
and a Cat D9 winch to pull
back of napkin 7+ inch
isn't 6" the largest pvc?
edit 12"+ at 40% fill
Last edited:
- Location
- Massachusetts
750 copper is the largest I have installed and I have removed old cloth covered 1,000 copper.
I can't imagine running 2,000. :happyno:
kwired
Electron manager
- Location
- NE Nebraska
I agree. Though more conductors will be needed handling 5-600's is also less labor intensive then 2000's, even for mechanical handling equipment. Might even make a difference in how big of a forklift or crane you will need just to handle raw material before you even get to installing it.
Fulthrotl
~Autocorrect is My Worst Enema.~
- Occupation
- E
longest large copper pull i've made was three 750 mcm's about 900' or so, iirc,
and it was in cable tray, with waterfalls, 90's, etc. in a refinery on a cogen project.
it was not a fun day at the park. the foreman running the crew managed to get a
6' loop in the middle of the run, coming off a waterfall...... they ended up using a
gutter in the cable tray, and splicing the things, after the foreman quit, anticipating
being fired.
Inductance is proportional to the log of seperation
So if less than 10 times as much it is moot
even at 100 times only doubles
at an increase of 10 times dist it is ignored
and the equation has multiple factors, some of which do not change, which further reduces the significance of seperation
d is dist between conductors
GMR geometric mean radius is a property of the conductor radius x e^-0.25
This equation is indicative only of the effect between one conductor pair. When the scenario is scaled up to a manifold real world situation the analysis will show many interactions some of which are constructive and some of which are destructive from the standpoint of EMI, RFI, energy transfer, inductive coupling, etc. If an orthogonal (to the runs) cross section is analyzed in the time domain one will find spatial field fluxes which are mutually self-cancelling that would best be represented by matrices in the complex plane.
In reality it is difficult to bridge the gap between such analysis and the field installation. I am unaware of any algorithmic or other approach that has attempted this.
This is a major reason for the unpopularity of isophase installations. The reality is that there are no significant reasons to not use and there are a host of reasons to use isophase installations where ever the spatial separation is minimal and non-metallic raceways are utilized. This is why the code felt compelled to include their endorsement of the approach.
The picture of the installation within a switchboard pull section from Iwire speaks louder than any words as to why we must embrace and not fear this solution.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Ok...so what is your response to my last post as well as others abut the derating/large conductor issues? Do you acknowledge that there are relatively few installations where this is practical? Yes it is easier, convenient, and neater for some installs, but you have to be in that sweetspot.
- Location
- Massachusetts
The major reason for the unpopularity of isophase installations is the fact that in the vast majority of installations the NEC prohibits them.
that was to illustrate that the effect is moot, regardless of the number of conductors the spacing effect is a log function, and only 50% of the value at that
and is extrapolated to 3 phases
and a bundled phase can be replaced by a single larger conductor since the f is in phase and using the GMR
a lot of words, very little said...really? lol
a matrix solution is useless, order of magnitude is all that matters and it is moot
just because you are not aware, does not mean that others are not
the reason for the 'unpopularity' is cost and waste of material, not physics or the inability to calculate some phantom value (as long as both methods are code compliant)
no one 'fears' anything, logic dictates a different approach
hence between 2 guys with >60 years experience and perhaps 1000 installations it was observed 6 times or <1%
the isophase method may have a place in unique scenarios but is not a substitute for the standard method
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I don't understand this comment--isophase doesn't restrict you to one conduit per phase (see the pretty picture iwire posted). So if you go above 6 CCC per phase, run more conduits. Same as in a mixed phase installation.Above 6 CCC and the derate is going to start hurting enough that it probably wont be worth those few minutes of gazing at the super neat organized conductors before putting the covers on
Cheers, Wayne
- Location
- Massachusetts
In my picture there are four current carrying conductors in each conduit which requires an 80% derate.
Had they been installed in the conventional way (A, B, C, N) there would be no need for derating.
Had they been installed in the conventional way (A, B, C, N) there would be no need for derating.
- Status