What size wire and conduit 1449A, 3 phase system?

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jaehlee99

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Hello friends!!

I am sizing the conduit of system with 208Y/120V, 4W, 173888 VA per phase in the facilitiy.

Load calculaiton = 173888 VA /120 V = 1449 A

Cable size = 1449/0.8= 1811 A (use NEC 310-16, 194 F, THHW Al)

No. of cable = 6 x 400 kcmil

My question is that each conduit need contain all three phases along with a neutral and all the parallel runs need to be of the same size and length. I have done as follows:

- Area of 400kcmil THHW cable: 0.6619 in^2 (from NEC2011 Table 5)
- Size of PVC conduit: 1 1/2" (from NEC2011 Table 4)

Finally, I have 6 parallel runs of 1 1/2" PVC with runs of (6) 400 kcmil THW Al coductors and (1) #3/0 AL ground conductor on each conduit. I am not qute sure this is right calculation. Also, is ground conductor like neutral conductor every conduit?

If I am wrong, would you recommend the other way.

Thanks in advance
 
Are these conductors service conductors or feeder conductors? Also you can't use the 90?C ampacity for anything other than derating purposes. Only one 400 kcmil will fit in an 1 1/2" conduit.
 
Also, what is the size of the OCPD for the feeder or service?

The #3/0 AL gnd would only be good for an 800A feeder, and yes, a ground would be required in each conduit.
 
Many thank Don,

This conductor is not service but feeder conductor. Is there big difference for both case?

Based upon your recommendation, after calculating using 75?C again, the current capacity of 400 kcmil will be 270A. Each coduit will contain three phase, neutral and ground. SO placing five conductor for each conduit needs the area of 3.31 in ^2 ( 5X 0.6619 in ^2), therefore six runs of conduits would be 3 1/2 ". Is that right?

Regarding OCPD, I also applied 2000AT, it was also from 1449/0.8. The #3/0 AL gnd for an 800A feeder only you mentioned that.

Do I need to increase the ground wire?
 
I see you are in Canada so not sure about the rules up their. My comments are based on the NEC. If the overcurrent protective device is 2000 amps, you don't have enough conductor. You need conductors with a total ampacity of at least 2000 amps. The NEC would require a 400 kcmil aluminum or 250 kcmil copper Equipment Grounding Conductor in each conduit if the OCPD is 2000 amps.
 
jaehlee99 said:
Many thank Don,

This conductor is not service but feeder conductor. Is there big difference for both case?

Based upon your recommendation, after calculating using 75?C again, the current capacity of 400 kcmil will be 270A. Each coduit will contain three phase, neutral and ground. SO placing five conductor for each conduit needs the area of 3.31 in ^2 ( 5X 0.6619 in ^2), therefore six runs of conduits would be 3 1/2 ". Is that right?

Regarding OCPD, I also applied 2000AT, it was also from 1449/0.8. The #3/0 AL gnd for an 800A feeder only you mentioned that.

Do I need to increase the ground wire?
Click to expand...

For a feeder with a greater than 800A OCPD, the ampacity of the conductors will need to be equal or greater than the OCPD (NEC 240.4(C)). The ground conductor must be sized Per Table 250.122 (400mcm AL for a 2000A OCPD), and must be run in each conduit of your parallel conductors per 250.122(F).

So you would need 6 sets of 4#600mcm (340*6=2040) and one #400mcm AL G in each conduit.

The sizing (per table 5) for THHW would be (4 * 0.9729 in^2) + (0.6619 in^2) = 4.5535 in^2 total. Per Table 4, this would fit in a 4"PVC conduit.
 
david luchini said:
For a feeder with a greater than 800A OCPD, the ampacity of the conductors will need to be equal or greater than the OCPD (NEC 240.4(C)). The ground conductor must be sized Per Table 250.122 (400mcm AL for a 2000A OCPD), and must be run in each conduit of your parallel conductors per 250.122(F).

So you would need 6 sets of 4#600mcm (340*6=2040) and one #400mcm AL G in each conduit.

The sizing (per table 5) for THHW would be (4 * 0.9729 in^2) + (0.6619 in^2) = 4.5535 in^2 total. Per Table 4, this would fit in a 4"PVC conduit.
Click to expand...

why does he need a full size neutral?

since this is PVC why would he have to run a set in each conduit?
 
If I'm not mistaken, 300.3(B) and 310.4(C) would both require all conductors in each conduit (assuming he needs the grounded conductor)
 
petersonra said:
It appears that only underground PVC conduits can be run isolated phase.

see exception after 300.3 (B) (1).
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It is my opinion that the exception to 300.3(B)(1) is not needed as 300.3(B)(3) permits isolated phase installations in all locations....however the code making panel does not agree with me.:)
 
HTML: 
why does he need a full size neutral?

since this is PVC why would he have to run a set in each conduit?
petersonra
If I choose not PVC but Magnetic conduit, does it need to be run a neutral ?
 
jaehlee99 said:
HTML: 
why does he need a full size neutral?

since this is PVC why would he have to run a set in each conduit?
petersonra
If I choose not PVC but Magnetic conduit, does it need to be run a neutral ?
Click to expand...

You always need to run a neutral if it is used down stream.

If you use some kind of metal conduit or EMT you would not need an EGC.

I have personally often wondered why such huge feeders are run in the first place. it seems like it ought to be more efficient and more cost effective to run higher voltage closer to the load and set transformers closer to the loads.
 
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I have personally often wondered why such huge feeders are run in the first place. it seems like it ought to be more efficient and more cost effective to run higher voltage closer to the load and set transformers closer to the loads.
Click to expand...

Our client has asked us to use an outdoor transformer because this building is chemical plant.

In addition, I have to consider a voltage drop when electricity is delivered from the outdoor transformer across the cable to load due to more than 100ft distance.

For the EGC and GEC, if a transformer has either OCPD or w/o OCPD at the primary side of the transformer, I was wondering what the code is applied to it ?

Also, where is the connection point between GEC and EGC ?
 
I'm afraid I've gotten lost..... A few questions, if I may...
Is the transformer utility owned/fed or customer owned/fed
Your transformer secondary feeds a 2000 amp OCP device, correct ?
(6) runs of 400 kcmil Cu, correct ?
What size transformer ?
Calculated neutral load ?
What size OCP is on the transformer primary ?
Is there OCP on the secondary prior to the 2000 amp device in the building ?
 
Is the transformer utility owned/fed or customer owned/fed => utiliity owned

Your transformer secondary feeds a 2000 amp OCP device, correct ? = Yes

(6) runs of 400 kcmil Cu, correct ? => Yes

What size transformer ? => 1500 kVA

Calculated neutral load ? It need to be calculated

What size OCP is on the transformer primary ? 50A

Is there OCP on the secondary prior to the 2000 amp device in the building ? No
 
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jaehlee99 said:
Is the transformer utility owned/fed or customer owned/fed => utiliity owned <br>
Click to expand...
O.K., If it's utility owned transformer, IMO, you have service conductors, not feeders to your 2000 amp service main.
jaehlee99 said:
Your transformer secondary feeds a 2000 amp OCP device, correct ? = Yes<br>
Click to expand...
Sevrice disconnect then [/QUOTE]<br>
jaehlee99 said:
(6) runs of 400 kcmil Cu, correct ? => Yes <br>
Click to expand...
Looks correct, 2010 amps[/QUOTE]<br>
jaehlee99 said:
What size transformer ? => 1500 kVA<br>
Click to expand...
k
jaehlee99 said:
Calculated neutral load ? It need to be calculated <br>
Click to expand...
Your neutral conductors would only need to be sized to carry that load, minimum of 1/0.
jaehlee99 said:
What size OCP is on the transformer primary ? 50A<br>
Click to expand...
If it's utility owned, the size would normally be up to them.
jaehlee99 said:
Is there OCP on the secondary prior to the 2000 amp device in the building ? No
Click to expand...
Reenforcing that you have service conductors.
Since you are dealing with a service your neutral conductors will serve as the ground for your service equipment and there is no need for a EGC from the transformer. You will have a bonding jumper at your servoice and the grounded/grounding connection will be made there.


The above is base on NEC and US methods. I can not testify about Canadian changes.
 
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Augie47

Thanks a lot for taken your time, i do really appreciated your help.

Would you elaborate on this ?

O.K., If it's utility owned transformer, IMO, you have service conductors, not feeders to your 2000 amp service main.
Click to expand...

Best Regards

John
 
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I'm a little confused. You said 208y 120. Then you used 120 to calculate amps. Now you say
1500 kva xfmr. Can someone clarify what I'm missing?
 
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