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#23947 - 03/31/03 09:56 PM Overkill
CTwireman Offline
Member

Registered: 02/07/02
Posts: 839
Loc: Connecticut, USA
I have seen many examples of overkill and I often wonder if those who design and install electrical systems ever stop to think about the downsides to overkill.

I have read plenty of spec books where 3/4" conduit is the minimum size allowed, yet many of these conduits will only contain 3 to 5 #12 conductors. I never understood why engineers do this. On a job with tens or hundreds of thousands of feet of pipe, this adds up to a lot of extra money!

But another downside is not so apparent. What about the unnecesary consumption of resources? Sure, I know what you are thinking: copper and iron ore are in great abundance and realtively inexpensive at the moment. However, the problem is not with the resource itself, but the energy required to produce the resource. And energy, as we all now, must come from fossil fuels, nuclear, or hydro means.

I guess it's hard to convice people to conserve when a coil of 12/2 is $18 and a stick of 3/4 is $1.75.

Well, I'm going to keep doing my part. Reduce, reuse, recylce. Yes, this works with electrical stuff, too. Am I way off base here?

I hope everyone doesn't think I'm a tree-hugging nut after this.

Peter




[This message has been edited by CTwireman (edited 04-01-2003).]
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#23948 - 03/31/03 10:00 PM Re: Overkill
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Peter,
Maybe the specifiers are betting on using the extra space in the conduits, for future expansion, in case more wires have to be pulled in later.
That would be my guess!
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#23949 - 03/31/03 10:04 PM Re: Overkill
SvenNYC Offline
Member

Registered: 08/19/02
Posts: 1685
Loc: New York City
I'm a big proponent of over-engineering if you have the budget.

It allows for easier alterations and room for expansion.

In the long run it may be cheaper to install a fat conduit than have to tear out all the skinny conduit and install fat pipe when you need to run additional circuits in that location.

The environmental impact you cite, however shuold make one think twice about just tossing things out.

How many people here collect all the old copper wire you remove and scrap steel pipe to sell to a recycling plant?

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#23950 - 03/31/03 11:00 PM Re: Overkill
txsparky Offline
Member

Registered: 05/25/01
Posts: 578
Loc: Magnolia,.Texas U.S.A.
I've had many jobs where the minimum size pipe was 3/4",seperate bonding conductor,and steel compression fittings (all indoors )

My take on this is that the engineers fee is based on a percentage of the total project cost and more expensive materials put more money in their pockets. On the other side of the coin, it also puts more money in the contractors pocket on their percentage of material mark-ups.
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#23951 - 03/31/03 11:46 PM Re: Overkill
nesparky Offline
Member

Registered: 06/21/01
Posts: 650
Loc: omaha,ne
I also have seen many spec on jobs requiring 3/4 conduit as smallest size on job, seperate ground wire in all conduits, and steel compression fittings.
While some designers are trying to run up the cost of the job to get a bigger percentage, most are trying for a better quality installation.
3/4 conduit allows for adds and changes especally after this project is finished and a new one is added in the same area. A seperate ground wire means that you do not lose ground continuity because some one forgot to tighten a coupling or connector, or if the conduit comes apart for some other reason. Steel fitting are to eleminate dissimular metal possible problems with corrosion. Compression fittings are usually more likely to be tightened during installs.
Or so an engineer told me when I asked him why those were his canned specs.
Still think the percentage of cost is part of the reason, but he does make a point or two.
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ed

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#23952 - 04/01/03 12:24 AM Re: Overkill
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I do not find much labor difference and the material cost is not that much more so I almost never run 1/2" you just can not get much in it.

As far as resources think of the added resources used when you come back and run another pipe right beside the first when the customer wants to add something.

If I could save some resources it would be the 2 - 4" conduits the phone company always wants, one for "spare" and one with a 25 pair cable the size of 10/3 NM. We pull 4 - 600kcmils in 3" EMT and these guys want a pipe they can walk through.
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#23953 - 04/01/03 05:31 AM Re: Overkill
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
In my opinion the 3/4" spec is left over from the days of THW wire. In many cases, you can't fill the 3/4" to maximum because of the derating rules. The fill for 1/2" with #12s is 9. If they are all current carrying conductors, you can't really put any more than than in the raceway because when you get to the 10th current carrying conductor the #12 must be put on a maximum 15 amp breaker. As far as pulling the wire in, I agree that it always seems to pull easier with a larger raceway, but does it really pull easier?. I've never seen a factor for raceway size in any of the wire pulling force calculations. If it really made a difference, shouldn't the raceway size be a factor in the pulling calculation?
Don
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#23954 - 04/01/03 09:55 AM Re: Overkill
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
From an engineering point of view:

By increasing the diameter of a pipe (e.g. conduit) by 50% the area increase 125%. However, the material used increase by only 50%, assuming the same wall thickness. If you were to put two of the orginal pipes side by side, the increase in both area and material would be 100%.

I doubt oversize conduit is a big environmental load. Oversizing cables is a bigger issue I think, as copper is not very healty. Nor is PVC.

Peter,
I think tree huggers are good for the electrical business: Electricity is (or at least looks) clean and its share of the total energy usage increase every year. If this development continues, everything will soon run by electricity.

The Arabs have realised this and are investing in solar power and power lines to export electric power.

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#23955 - 04/05/03 01:37 PM Re: Overkill
Weekend Offline
Junior Member

Registered: 03/27/03
Posts: 3
Loc: Missouri
I can't tell you how many times I have had to run new conduit because the contractor used the minimum size and it won't allow three # 12 thhn conductors. I don't blame the contractor I blame whoever is in charge. Planning is always a great idea. But then the guy or gal in charge is never the one running conduit in the ceiling of the un-airconditioned power plant in July! If they did it just once they would always allow for future use.

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#23956 - 04/06/03 04:31 PM Re: Overkill
harold endean Offline
Member

Registered: 02/16/02
Posts: 2248
Loc: Boonton, NJ
I was working on a job where the specs called for raintight fittings on all of the pipe inside of the building. I am not sure if they thought it was a better ground or if the expected water leaks above the grid ceiling?

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