What size wire and conduit 250 amp 3 phase ?

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Old 02-18-11, 10:13 PM
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What size wire and conduit 250 amp 3 phase ?

I am installing an underground 400 amp 3 phase 4 wire 120/240 electrical service for a farm bldg. The first leg of the service is 210 ft. from the pole. Our service provider(PG&E) required me to install 5" conduit. They are providing the cable (1000 A TPX aluminum cable) which they tell me is 1000 amp and the largest they use. I am required to put a service panel w/ 13 jaw meter socket and separate pull section. These two panel boxes for the 400amp service together are just giant , almost 8 feet tall and 5 feet wide and cost me 0ver $4k without any breakers!
From these panels I need to start another 200ft leg to my bldg. I figured a 250 amp 3 phase wire service panel at this point will do. Any idea what size wire and conduit I can get away with for this 200 ft run? It would be nice if I could run something smaller then 5" conduit and some reasonably sized wire. Thanks NIck
 
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Old 02-18-11, 10:40 PM
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Three phase is more often 208/120 volts rather than 240/120 volts. Minimum size aluminum wire would be 300 kcm and 3 inch conduit.
 
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Old 02-18-11, 10:44 PM
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350 or 400 kcml xhhw aluminum. min 3" conduit...you beat me to it.
 
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Old 02-19-11, 08:08 AM
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In my area this size service would require engineered plans and load calculations. They're letting the homeowner/farmer do this without a master electrician or EE?
 
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Old 02-19-11, 09:31 AM
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I don't see this as a DIY project at all and it's definitely not residential so this feeder should be fully rated and increased in size for volatge drop. I would probably run parallel 2 1/2" or 3" PVC conduits and parallel 3/0 Al XHHW phase conductors and #4 Al XHHW ground conductors. The larger conduits will make the pull easier for that distance. Since it's a farm, you could consider running it overhead.
 

Last edited by CasualJoe; 02-19-11 at 09:37 AM. Reason: added info
  #6  
Old 02-19-11, 10:11 AM
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Originally Posted by CasualJoe View Post
I don't see this as a DIY project at all and it's definitely not residential so this feeder should be fully rated and increased in size for volatge drop. I would probably run parallel 2 1/2" or 3" PVC conduits and parallel 3/0 Al XHHW phase conductors and #4 Al XHHW ground conductors. The larger conduits will make the pull easier for that distance. Since it's a farm, you could consider running it overhead.
the problem with that is 3/0 is too small.3/0 a/ is only good for 175 amps.also each of the paralell wires need to be cappable of carring the load if one wire of the pair goes open.
 
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Old 02-19-11, 11:09 AM
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also each of the paralell wires need to be cappable of carring the load if one wire of the pair goes open.
Where the heck did you dig up that little tidbit of misinformation? The whole purpose of using parallel wiring is to allow higher currents than single conductors are capable of carrying. You DO need to have each conduit contain all three phases along with a neutral and all the parallel runs need to be of the same size and length but there is NO requirement that each run must be able to carry the entire current flow.
 
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Old 02-19-11, 11:47 AM
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Originally Posted by Furd View Post
Where the heck did you dig up that little tidbit of misinformation? The whole purpose of using parallel wiring is to allow higher currents than single conductors are capable of carrying. You DO need to have each conduit contain all three phases along with a neutral and all the parallel runs need to be of the same size and length but there is NO requirement that each run must be able to carry the entire current flow.
310.4(b) the ampacity of each individual conductor is suffecnt to carry the entire load
current shared by parralell conductors.also read(c).paralelling is done to reduce voltage drop.
i dug it up in the misinformation tidbit section of the nec.
 

Last edited by oleguy; 02-19-11 at 12:09 PM.
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Old 02-19-11, 12:22 PM
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Originally Posted by oleguy View Post
310.4(b) the ampacity of each individual conductor is suffecnt to carry the entire load
current shared by parralell conductors.also read(c).paralelling is done to reduce voltage drop.
i dug it up in the misinformation tidbit section of the nec.
I really wish i had my code book in front of me. But this is a total misinterpertaion of the code. This only applies to the neutral conductors. If you still think that it applies, then answer me this. How would you supply power to a 4000 amp service from a transformer pad? Show me the size conduit and wire you would need for an INDIVIDUAL conductor to be rated for 4000 AMPS!!! as casualjoe stated, parallelling is used to reduce wire and conduit sizing for larger ampacity.

also, its widely understood that article 310 and article 250 are the 2 most widely misinterperted and misunderstood articles in the NEC
 
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Old 02-19-11, 12:40 PM
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Originally Posted by ElectricJoeNJ View Post
I really wish i had my code book in front of me. But this is a total misinterpertaion of the code. This only applies to the neutral conductors. If you still think that it applies, then answer me this. How would you supply power to a 4000 amp service from a transformer pad? Show me the size conduit and wire you would need for an INDIVIDUAL conductor to be rated for 4000 AMPS!!! as casualjoe stated, parallelling is used to reduce wire and conduit sizing for larger ampacity.

also, its widely understood that article 310 and article 250 are the 2 most widely misinterperted and misunderstood articles in the NEC
then get your code book!!! 310.4 (C)the overcurrent protection is such that the ampicity of each individual conductor will not be excceded if one or more parrelell conductors become inadvertnaly disconnected..
 
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Old 02-19-11, 12:59 PM
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Originally Posted by oleguy View Post
then get your code book!!!
Ok.... Now im gonna try and remain calm for this. Im going to ASSume that when you wrote 310.4(b) you were actually referring to 310.4(A) exception no. 1(B). This is where PROPER reading and UNDERSTANDING of the code come into play. 310.4(a) exception no.1 states " conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices provided ALL of the following apply. You stated that subsection (b) applies to this OP discussion. (B) states " the ampacity of each individual conductor is sufficient to carry the entire load current shared by the parallel conductors.

Now, do you care to retract your previous statements. Next time do your research before you try and help, or not help someone.
 
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Old 02-19-11, 01:03 PM
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STOP, your beginning to sound like a real idiot.

Originally Posted by oleguy View Post
then get your code book!!! 310.4 (C)the overcurrent protection is such that the ampicity of each individual conductor will not be excceded if one or more parrelell conductors become inadvertnaly disconnected..
DO you happen to notice the TEXT for what your quoting is typed differently. ITS because its an EXCEPTION for running parallel conductors SMALLER than 1/0 AWG.

Your obviously not an electrician, please stop trying to give help in the Electrical forum
 
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Old 02-19-11, 01:03 PM
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You cannot just pick things randomly from the code. Read the ENTIRE Article 310.4 NOT just one paragraph. The (b) and (c) you refer to ONLY pertain to Exception no. 2 which states:
"Conductors in sizes smaller than 1/0 AWG shall be permitted to be run in parallel to supply control power to indicating instruments, contactors, relays, solenoids, and similar control devices provided..."


The example under discussion does NOT in any way, shape or form come under the exceptions that you are submitting.
 
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Old 02-19-11, 01:06 PM
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Furd, its actually exception no.1 please dont give this guy any more ammo
 
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Old 02-19-11, 01:25 PM
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first off casualjoe said 3/0 al.that is only good for 175 amps.ckt needs at least 350kcml.
 
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Old 02-19-11, 01:33 PM
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310.4 Conductors in Parallel.
(A) General. Aluminum, copper-clad aluminum, or copper
conductors of size 1/0 AWG and larger, comprising each
phase, polarity, neutral, or grounded circuit conductor shall
be permitted to be connected in parallel (electrically joined
at both ends).
Exception No. 1: Conductors in sizes smaller than 1/0
AWG shall be permitted to be run in parallel to supply
control power to indicating instruments, contactors, relays,
solenoids, and similar control devices, or for frequencies of
360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or
cable.
(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.
(c) The overcurrent protection is such that the ampacity
of each individual conductor will not be exceeded if one
or more of the parallel conductors become inadvertently
Exception No. 2: Under engineering supervision,
grounded neutral conductors in sizes 2 AWG and larger
shall be permitted to be run in parallel for existing
installations.
FPN to Exception No. 2: Exception No. 2 can be used to
alleviate overheating of neutral conductors in existing installations
due to high content of triplen harmonic currents.
(B) Conductor Characteristics. The paralleled conductors
in each phase, polarity, neutral, grounded circuit conductor,
or equipment grounding conductor shall comply
with all of the following:
(1) Be the same length
(2) Have the same conductor material
(3) Be the same size in circular mil area
(4) Have the same insulation type
(5) Be terminated in the same manner
(C) Separate Cables or Raceways. Where run in separate
cables or raceways, the cables or raceways with conductors
shall have the same number of conductors and shall have
the same electrical characteristics. Conductors of one
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor shall not be required to
have the same physical characteristics as those of another
phase, polarity, neutral, grounded circuit conductor, or
equipment grounding conductor to achieve balance.
(D) Ampacity Adjustment. Conductors installed in parallel
shall comply with the provisions of 310.15(B)(2)(a).
(E) Equipment Grounding Conductors. Where parallel
equipment grounding conductors are used, they shall be
sized in accordance with 250.122. Sectioned equipment
grounding conductors smaller than 1/0 AWG shall be permitted
in multiconductor cables in accordance with 310.13,
provided the combined circular mil area in each cable complies
with 250.122.
310.5 Minimum Size of Conductors. The minimum size
of conductors shall be as shown in Table 310.5, except as
permitted elsewhere in this Code.
Table 310.5 Minimum Size of Conductors
Conductor
Voltage Rating
(Volts)
Minimum Conductor Size (AWG)
Copper
Aluminum or Copper-Clad
Aluminum
02000 14 12
20018000 8 8
800115,000 2 2
15,00128,000 1 1
28,00135,000 1/0 1/0
310.1 ARTICLE 310 CONDUCTORS FOR GENERAL WIRING
7
...................................
 
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Old 02-19-11, 01:36 PM
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Originally Posted by oleguy View Post
first off casualjoe said 3/0 al.that is only good for 175 amps.ckt needs at least 350kcml.
CasualJoe stated PARALLEL 3/0 runs of aluminum. Using parallel runs (two) means the current divides equally on each run therefore the Ampacity of two runs of 3/0 becomes 310 amperes using the 75 degree C. column.

ElectricJoeNJ, I'm retired and I only have a 2002 code book. Not that it matters THAT much since oleguy is just plain in error on this topic.
 
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Old 02-19-11, 01:39 PM
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Originally Posted by oleguy View Post
first off casualjoe said 3/0 al.that is only good for 175 amps.ckt needs at least 350kcml.
Your totally mistaken.. When are you gonna stop saying stupid things, please im starting to get annoyed. your not an electrician, youve never worked as electrician, and you have no idea what your talking about.
 
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Old 02-19-11, 01:47 PM
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Lets keep it friendly guys. I've posted the 2008 above so you can all quote from the same source.
 
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Old 02-19-11, 01:54 PM
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your right ray sorry for getting annoyed but this guy is ridiculous. To get back on track and help the OP out

2 parallel runs of 2 1/2" or 3" PVC with runs of (4) 3/0 AL XHHW conductors and (1) #4 AL XHHW ground conductor on each conduit. I also recommend using rigid sweeps in your conduit runs to make the wire pulling easier.

Ray, since theres nothing else to discuss or argue here you can lock this thread, if the OP has any more questions he can PM us or start a new thread.
 
  #21  
Old 02-26-11, 12:22 AM
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I can understand where this going however let me add a final comment in here normally the Three phase DELTA system is not really a DIY item at all due there are quite few codes we have to follow and there is not much margin of error on this and really IMO for non resdentail farm building are classfied as commercal building {I know they do that in state of Wisconsin } so it will be wiser to have a Electrician to come out and help you on this matter.

Any more issue or other question please do PM me or other moderators.

I will leave this thread locked for now
 
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