Size grounded conductor for a service

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sokkerdude

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I have a 3000 amp 480 volt 3 phase 4 wire service feeding a pump station.
There is no 277 v in the project, everything is 3 phase. My qestion is can I reduce the size of the grounded conductor?
If the load on the neutral or grounded conductor is zero ? Does Article 230.42 (c) apply?
 
sokkerdude said:
I have a 3000 amp 480 volt 3 phase 4 wire service feeding a pump station.
There is no 277 v in the project, everything is 3 phase. My qestion is can I reduce the size of the grounded conductor?
If the load on the neutral or grounded conductor is zero ? Does Article 230.42 (c) apply?
Click to expand...
3/0 copper or 250 kcmil aluminum. The size is based on the size of the service entrance comductors. Then you go to table 250.66
 
sokkerdude said:
I have a 3000 amp 480 volt 3 phase 4 wire service feeding a pump station.
There is no 277 v in the project, everything is 3 phase. My qestion is can I reduce the size of the grounded conductor?
If the load on the neutral or grounded conductor is zero ? Does Article 230.42 (c) apply?
Click to expand...
Yes you can! just follow the what pismo said. A neutral is required to be brought to the service equipment.
 
3/0 copper is not large enough for this application. It must not be less than 12.5% of the size of the service entrance conductors. 3000 amps will require at least 1900.8 kcmil (18 sets of 1/0). This would require a 250 kcmil neutral, but since 1/0 is the smallest you can install in parallel you would needed 18 1/0 neutrals. It appears that no matter what size you use for the phase conductors you will need a 1/0 grounded conductor in each raceway.
Don
 
sokkerdude said:
I have a 3000 amp 480 volt 3 phase 4 wire service feeding a pump station.
There is no 277 v in the project, everything is 3 phase. My qestion is can I reduce the size of the grounded conductor?
If the load on the neutral or grounded conductor is zero ? Does Article 230.42 (c) apply?
Click to expand...

I am curious as to why you are running a 3ph 4wire service when all you need is 3ph, 3wire?
 
don_resqcapt19 said:
3/0 copper is not large enough for this application. It must not be less than 12.5% of the size of the service entrance conductors. 3000 amps will require at least 1900.8 kcmil (18 sets of 1/0). This would require a 250 kcmil neutral, but since 1/0 is the smallest you can install in parallel you would needed 18 1/0 neutrals. It appears that no matter what size you use for the phase conductors you will need a 1/0 grounded conductor in each raceway.
Don
Click to expand...
You're correct. I forgot about that. I can't remember the last time I haven't pulled all the same size conductors including the neutrals. It seems it's always that way on the approved plans. I haven't done a job in a long time that has only 3 phase loads I guess.
 
pismo said:
Because 250.24 requires it. I think the requirement is fairly new. I think the 1999 NEC.
Click to expand...

What I was trying to get to, is that you are only going to run 4 conductors (3ungrounded/1 grounded) and your not going to run an additional ground, right? .:D
 
kingpb said:
What I was trying to get to, is that you are only going to run 4 conductors (3ungrounded/1 grounded) and your not going to run an additional ground, right? .:D
Click to expand...
That's correct. The utility grounds the grounded (neutral) at their transformer.
 
don_resqcapt19 said:
3/0 copper is not large enough for this application. It must not be less than 12.5% of the size of the service entrance conductors. 3000 amps will require at least 1900.8 kcmil (18 sets of 1/0). This would require a 250 kcmil neutral, but since 1/0 is the smallest you can install in parallel you would needed 18 1/0 neutrals. It appears that no matter what size you use for the phase conductors you will need a 1/0 grounded conductor in each raceway.
Don
Click to expand...
If you use 500 kcm for the phase conductors it would take 3000/380=7.9
or 8 ckts. Using table 250.66, 500 requires a 1/0 conductor as you say. What do you mean by (18 sets of 1/0). There used to be a note to the 12.5% in the table but now I think its covered on note 1.
 
Bob,
What do you mean by (18 sets of 1/0).
Click to expand...
That would be the least amount of copper for a 3000 amp circuit. 1/0 has an area of 105,600 circular mils. 18 sets would be 1900.8 kcmil per phase. With 8 sets of 500 kcmil, you will have 4000 kcmil per phase.
Don
 
don_resqcapt19 said:
Bob,

That would be the least amount of copper for a 3000 amp circuit. 1/0 has an area of 105,600 circular mils. 18 sets would be 1900.8 kcmil per phase. With 8 sets of 500 kcmil, you will have 4000 kcmil per phase.
Don
Click to expand...
18 1/0 has an ampacity of 2700 amps per phase. 8 #500 kcm has an
ampacity of 3040 amps.
 
Bob,
I guess I jumped down to the ampacity of 2/0 when I did my calcs. In any case, even using 20 1/0s to get 3000 amps, the total copper is 2112 kcmil, a bit more than half of what you need when using 500 kcmil. I only went in that direction to get the minimum size of the grounded conductor for a 3000 amp service. The minimum is 12.5% of the largest ungrounded phase conductor. If you could install the service where you only needed a single grounded conductor, you would need a 300 kcmil for the 1/0s and a 500 kcmil for the 500s
Don
 
Perplexed!

Perplexed!

pipemaster said:
Yes you can! just follow the what pismo said. A neutral is required to be brought to the service equipment.
Click to expand...

What am I missing here? It seems that 250.20(B) and 250.21(4) would indicate that you do not need system grounding in this case. 205.24(A) Would mandate grounding electrode conductor and 250.24(E) would also apply. Would 250.24(B),(C),(D) even be applicable?
___________________
Wes Gerrans
Instructor
Northwest Kansas technical College
Goodland, KS
 
Wes if the service is to be grounded at any point 250.24(B) requires the grounded conductor to be brought to the service disconect

In this case the service is supplied by a Wye and Wye's are required to be grounded.
 
don_resqcapt19 said:
Bob,

This wye is not required to be a grounded system by 250.20(B).
Don
Click to expand...

Interesting.

I stand corrected.

I have never seen ungrounded Wye and wonder how it is possible as here the power company bonds XO to ground.
 
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