1000 kcmil or 750

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rconteng

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I am wondering whether it will make a difference to a contractor if he were asked to pull five parallel runs of 4 conductor 1000 kcmil cable in 5" conduits vs 6 runs of 4 conductor 750 kcmil in 4" conduits. The distance is roughly 600 feet.
 
rconteng said:
I am wondering whether it will make a difference to a contractor if he were asked to pull five parallel runs of 4 conductor 1000 kcmil cable in 5" conduits vs 6 runs of 4 conductor 750 kcmil in 4" conduits. The distance is roughly 600 feet.
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As an installer I would rather limit it to no larger then 600 Kcmil unless the enclosures have a lot of space.
 
Why 6 runs of 750? That is way more ampacity than is 4 runs of 1000. Six runs of 500 would do the job.
 
don_resqcapt19 said:
Why 6 runs of 750? That is way more ampacity than is 4 runs of 1000. Six runs of 500 would do the job.
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I am looking for 1,600 amps in total. According to the CEC in a buried conduit installation, 6 parallel runs of 750 kcmil aluminum or 4 parallel runs of 1,000 kcmil copper will do the job.
 
This may or may not be a factor, but the potential voltage drop for the 6x750 run may be less than that of the 5x1000.

Here's my calculation (not guaranteed to be correct, but idea pulled from Table 9 and calculation in Table 9 - Note 2):

Assuming 2000A total at 0.9 power factor for both scenarios...

Voltage drop in 5x1000 kcmil, 400A, 600 feet = 15.07 volts, 10.4kW wire heating loss per run
Voltage drop in 6x750 kcmil, 333A, 600 feet = 13.77 volts, 7.9kW wire heating loss per run

Difference in wire losses = (5 * 10.4kW) - (6 * 7.9kW) = 4.6kW

Calculated maximum long term electrical energy savings going with the 750 wiring = 4.6kW * 24 * 365 * 10 cents/kWhr = $4030/year.

Again, the above calculation could be wrong, but might be worth looking into this as a factor in your decision.

Nate.
 
the enclosures have a lot of space

the enclosures have a lot of space

Wire manufacturers have diagrams for how many round conductors fit in a round pipe. 7 and 19 were magic numbers, but they might have some rules of thumb for the mechanics of what you're doing.
 
the enclosures have a lot of space
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That is news to me and I work with them. :smile:

Here is a transformer before we installed the 600s.

It is roughly 4' W x 5' H

WHOITRANS1.jpg



Here it is after.

300KVA3LG.jpg


It was not easy getting all that in and I had a lot of room between the terminals and the bottom.
 
If this is for internal distribution for a Heavy Process or Industrial client, they may not want to utilize Aluminum conductors.
We do not allow them at our facility.
 
This is for the service conductors to a facility. The cost of aluminum is 1/3 of copper, so the owner is interested in the aluminum. I'm just trying to rationalize the cost of copper (using fewer runs, possibly saving labor, etc.). I appreciate the comments from the installers. As a designer, I'm sometimes guilty of not designing the most installer-friendly projects. The previous post's comments concerning the savings in $$ due to less losses is definitely worth noting.
 
Think about if you have to crimp lugs on these wires. A standard hypress only goes to 750 if you go to 1000 you may not have the crimping ability and may have to buy or rent a monster crimper.
 
I wouldn't even do a job with 1000 kcmil copper conductors and 5" conduit for the simple fact that the extra labor involved would far exceed running extra smaller conduits and pulling smaller conductors.
 
Total cross sectional area of copper required to push 1600 amps to 200 metres is 1200 sq mm (with less than 2.5 % voltage drop).

now i believe 1 kcmil = 0.507 mm2,

so 500kcmil = 253mm2 so 5 runs of 500 kcmil should be enough.

Cheers.
 
chaterpilar said:
Total cross sectional area of copper required to push 1600 amps to 200 metres is 1200 sq mm (with less than 2.5 % voltage drop).

now i believe 1 kcmil = 0.507 mm2,

so 500kcmil = 253mm2 so 5 runs of 500 kcmil should be enough.

Cheers.
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What does conductor cross sectional area have to do with ampacity when sizing feeders?
 
More cross sectional area, more current i guess...

More cross sectional area, more current i guess...

infinity said:
What does conductor cross sectional area have to do with ampacity when sizing feeders?
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Business of carrying current....:rolleyes:
 
rconteng,

Might be able to save some $$ if you could get the Utility transformer closer

than 600' away.

I would say most in the field would rather install more conduits with smaller

wire sizes. I see from 310.16 that 750kcmil Al ( 385 amps ) and 500kcmil Cu.

( 380 amps ) are about equal in ampacity.

1000kcmil Cu. conductors 600' long will be so heavy that just setting them up

will require a lot of labor, and band-aids,---ok, I think you know how I feel

about it.
 
chaterpilar said:
Total cross sectional area of copper required to push 1600 amps to 200 metres is 1200 sq mm (with less than 2.5 % voltage drop).

now i believe 1 kcmil = 0.507 mm2,

so 500kcmil = 253mm2 so 5 runs of 500 kcmil should be enough.

Cheers.
Click to expand...


infinity said:
What does conductor cross sectional area have to do with ampacity when sizing feeders?
Click to expand...

chaterpilar said:
Business of carrying current....:rolleyes:
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Not really. Parallel 250 kcmil conductors are rated for 255 amps at 75 degrees C. A 500 kcmil THHN conductor at 75 degree C is only rated for 380 amps for the same equivalent circular mil area. That gives you two ampacities (510 amps v. 380 amps) for the same 500 kcmil of conductor. Trying to use an amp per circular mils formula to size conductors will not work.
 
infinity said:
Not really. Parallel 250 kcmil conductors are rated for 255 amps at 75 degrees C. A 500 kcmil THHN conductor at 75 degree C is only rated for 380 amps for the same equivalent circular mil area. That gives you two ampacities (510 amps v. 380 amps) for the same 500 kcmil of conductor. Trying to use an amp per circular mils formula to size conductors will not work.
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The term "skin effect" comes to mind.;)

To the OP, I have never worked with 1000kcmil, and have only installed 750kcmil once, but I would agree with iwire. Keep wire size 600kcmil and below, you will be much more popular with the installers.
 
I thought "skin effect" comes into play only at high frequencies and is negligible at 60 Hz.

Thanks Infinity for that update... 6 conductors of 500 kcmil will be required (two 6 inch conduits with 3 conductors in each conduit).

Two smaller conductors will produce more heat than one bigger conductor of equivalent cross-sectional area.

as per Table 310.15(B) .2 the effect is pronounced only if number of conductors are more than 3 per conduit.
 
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Skin affect becomes and issue depending on which books you use with size above 300Kcmil other say 500kcmil.

That being said in the utility substation most of the bus work are either hollow or flat conductor
 
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