Most cost effective parallel conductor/raceway combinations?

Let me explain more: Example: 4000 ampere 3-phase supply

30 each 1/0 AWG 90 degree C copper conductors on 75 degree C terminals with three each conductors in each of 30 1 1/2 inch EMT raceways OR 13 each 500 kcmil 90 degree copper conductors on 75 degree terminals with three each conductors in each of 13 3 1/2 inch EMT raceways.

Assuming a 100 foot run of raceway with two factory sweep 90's one at each end with raceways supported by an existing unistrut pipe rack with clamps every six feet terminated at both ends at a Nema 1 enclosures which configuration is the least expensive for labor and material?

This is just one configuration. There would dozens if not hundreds of similar problems for supplies to 4000 amperes using 1/0 to 500 kcmil paralleled conductors and raceways.

I have onmore than one occasion asked the contractor on a job before I designed it. The answer depends on their capabilities & equipment. Some have no trouble pulling the larger wire, while others prefer running more conduits and keeping the wire size down.

It would be interesting to hear from the electricians on this.

Ben Miller

As a large commercial/industrial electrician for the past 30 years, I've had the privilege of building a lot of large switchgear from engineered drawings. Most blueprints called for 500MCM copper with 4 inch conduits. Usually busway after that. Actually, I've never paralleled anything less than 350's.

I think I am going to buy the Means estimating book and figure this sucker out. There has got to be a minimum price amongst the possible configurations. I remember one job where the engineer put a table right on the blue lines with all the parallel combinations for the desired load and left it up to the contractor to put in what ever he wanted. I did put together a JavaScript program that does parallel conductors for Table 310.16. It will help, but the output will have to be entered into a spreadsheet then the pipe sizes and costs will have to be entered. For 1/0 AWG to

500 kcmil there will be about 300 combinations for the loads from 600 amperes to 5000 amperes. I am certain someone has done this before. Maybe it is proprietary information.

I've never seen that, but it would be welcome.

Might be.

That's why I posted, as Ben requested, what I have seen over the years. 500's and 4 inch conduit seems to be the most cost effective. In your example:

Example: 4000 ampere 3-phase supply

30 each 1/0 AWG 90 degree C copper conductors on 75 degree C terminals with three each conductors in each of 30 1 1/2 inch EMT raceways OR 13 each 500 kcmil 90 degree copper conductors on 75 degree terminals with three each conductors in each of 13 3 1/2 inch EMT raceways.

Assuming a 100 foot run of raceway with two factory sweep 90's one at each end with raceways supported by an existing unistrut pipe rack with

clamps every six feet terminated at both ends at a Nema 1 enclosures which configuration is the least expensive for labor and material?

As an electrician, if given a choice, I would much rather run the 3 1/2 inch EMT. I can run 3 1/2" EMT just about as fast as I can run 1 1/2" EMT {Don't tell the Means people ;-)} Not so with rigid, though. I'd still rather run 13 runs of 3 1/2" steel rigid than 30 runs of 1 1/2" steel rigid. Same for the pulls. I'd rather pull and terminate 13 runs of 500's than 30 pulls and terminations of 1/0. I think the savings on labor would be in favor of the 500's. As far as time is concerned, IMO, there really isn't much difference between pulling 1/0 or 500's. Terminating 500's may take a little longer than 1/0, but one is also only terminating half as many sets. Not only that but keeping track of

90 conductors is definitely more time consuming than keeping track of

1. Additionally, I'd tend to think that a higher skill level would be required (meaning more $) to terminate 90-1/0's than 39-500's. In your example, If given a choice, I'd much rather run one run of busway. Might be harder to install, but at least there's no wire pulling.

You are right about the labor, but what about the material? 1/0 copper has an ampacity of 150 amperes

while 500 kcmil has an ampacity of 380 amperes (75 degree C.) or about 2.5 times 150 amperes.

500 kcmil has approximately 5 times the cross sectional area of 1/0 and by this should have 5 times the ampacity of 1/0 or an ampacity of 750 amperes.

This rule of diminshing retuns continues. For instance 1000 kcmil has an ampacity of 545 amperes but the area is 10 times that of 1/0.

So 1000 kcmil should have an ampacity of about 1500 amperes or 10 times 150 if all were linear. So the bottom line is the larger the wire size the more the cost per ampere.

I think this comes to this: the cost of copper per ampere for 500 kcmil verses 1/0 is double that of 1/0 and this trend holds for intervening wire sizes.

So after adding this in to the labor what is the optimum combination?

giganews wrote:

Because the price of copper has tripled in the last year or so, material costs are becoming more of a factor in the total price of parallel combinations. This appears to be a problem in linear programming, the type that would be in a text book for economics. Also, there is the problem of material availability and bulk prices. For instance, if I were to order conductors all of one size for a major job, I would get a better discount. One utility in Valdez, Alaska installs all 2/0 aluminum for underground service laterals parallel or otherwise. That is all they buy in bulk. This bulk buying becomes even more prevalent for metal clad cable used in large mines. Three $500 million mines that have recently been built in Alaska using almost all metal clad cables. The problem of running metal clad cable from a large transformer is complicated by the fact that using many parallel sets from the transformer to the switchgear requires a full sized equipment grounding conductor which is not in the cables unless they are special ordered. The engineers in these situations attempt to argue that the equipment grounding conductor in the cable in parallel with the metal sheath is sufficient to equal the full size grounding conductor which in many cases is debatable. For instance, let's say we are supplying 4000 amperes using 15 each 4/0 per phase. The required equipment grounding conductor is 400 kcmil. By code there should be a 400 kcmil in each cable but there isn't one.

After my wives started filing restraining orders against me and/or calling the cops, I started calling the cops first and claimed to be "the victim" of a beating by my wife. As you can see, when you click on the "Disposition" link at the top of the page, all but a few cases were dismissed by my wives because they knew what waited for them if they didn't.

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Open the url to get my court record which I am very proud of. It should look like the "text copy" below, if not, it timed out so you will have to type my name back in the empty spaces then just hit "submit" and it will come back up. Just click on the court case number to get more info on me. Yep, I learned quick on how to beat my wives into doing what I wanted them to do, then claimed to be the victim, but you will see I DID PLEAD NO CONTEST (meaning that I was guilty and not going to contest the charges) A COUPLE OF TIMES BECAUSE THE EVIDENCE WAS TOO STRONG AGAINST ME.

Court View 2000 - Public Access

On 19 Dec 2006 04:59:52 -0800, "jerry " Gave us:

Take your retarded horseshit somewhere else.

After my wives started filing restraining orders against me and/or calling the cops, I started calling the cops first and claimed to be "the victim" of a beating by my wife. As you can see, when you click on the "case numbers" then go up to the top and click on "Dispositions" my wives dropped all of the cases against me, except a couple where I had to plead "No Contest" which means I pleaded guilty and didn't contest the charges because the evidence was too strong.

My wives are Alaskan native women and Alaska has the highest rate of Rape in the nation...We men Know How to treat women here and the courts let us.

I'm very proud of my record. So here is the link to it. It times out quickly so just type my name in the top I.D. two boxes and leave the rest open then click "submit" and you will get the info seen here in my "Text Copy" which info has links that you can click.

COURT RECORD OF GERALD NEWTON Court View 2000 - Public Access

On 19 Dec 2006 05:14:58 -0800, "jerry " Gave us:

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That is aside from the fact that your tripe now falls under the moniker of SPAM.

Don't make me have WEBTARDTV kill your account, you stupid f*ck.