# Spacing of conduits must be maintained.



## pete87 (Oct 22, 2012)

Damm the 2008 Handbook ... I could only get the 15th edition on line ...

Looking for early 1970"s Handbook ... but did not want to purchase .
Spacing concrete ... diagrams 

The only spacing i have kept on trapeze ... was minimal , allowing for straps .

In the ground ... again just with standard spacers for pipe bank , in concrete standard spacers .







Pete


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## Pete m. (Nov 19, 2011)

I wonder if it would depend on the size of raceway and conductor within if in a trench.

I could see where raceways stacked together (maintaining no spacing) in a trench could have additive heating. 

Although, for example, using multiple 1" raceways (all underground) that contained 3 - #8 conductors the conductors would tend to settle at the bottom of each raceway and would maintain some spacing from other conductors in adjacent raceways even if those raceways were in intimate contact.

Secondly, I suppose the ambient temperature of the earth itself (measured at trench depth) would have to reach 87 degrees F before deration would be required.

Pete


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## cabletie (Feb 12, 2011)

I could see that everything would be fine if each conduit only fed one piece of equipment. There would only be one circuit in each conduit. It would probably not generate to much heat. 

But what about a conduit with branch circuit home runs. Let's say there were several 1-1/4" conduits each with 20 #10's on 20 amp breakers. How much heat would the earth be able to dissipate? Would a conduit width spacing be enough? Would no spacing be enough?


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## Pete m. (Nov 19, 2011)

cabletie said:


> I could see that everything would be fine if each conduit only fed one piece of equipment. There would only be one circuit in each conduit. It would probably not generate to much heat.
> 
> But what about a conduit with branch circuit home runs. Let's say there were several 1-1/4" conduits each with 20 #10's on 20 amp breakers. How much heat would the earth be able to dissipate? Would a conduit width spacing be enough? Would no spacing be enough?


In your example I still don't know how big the concern would be. The 10's are already derated 50% based upon the number of CCC's in each raceway. 

I found a chart that indicated that the "mean" ground temperature in central Ohio is listed at approximately 53 degrees. In fairness, the chart didn't indicate at what depth this "mean" temperature was calculated.

Pete


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## Southeast Power (Jan 18, 2009)

Underground duct bank racks don't have much between them.
I dont expect you would be tighter than that even if you used 7/8" unitstrut between racks.


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## pete87 (Oct 22, 2012)

jrannis said:


> Underground duct bank racks don't have much between them.
> I dont expect you would be tighter than that even if you used 7/8" unitstrut between racks.




The Lego Type Plastic Connecting Spacers ... allow for a Pencil Vibrator to fit between conduits ... to ensure concrete coverage .



Pete


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## JW Splicer (Mar 15, 2014)

For transmission and distribution, yes. For under 600V why even bother? If you had to have armored single core cable for T&D or a single phase per conduit in a ferrous raceway then you absolutely have to derate.


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## pete87 (Oct 22, 2012)

Here is an old spacing chart by MD for panels ect 



.http://i114.photobucket.com/albums/n277/mdshunk/conduit20spacing2.jpg




Pete


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## RIVETER (Sep 26, 2009)

cabletie said:


> I have always spaced conduits in a trench. I try not to bundle conduits because of heat. There are times I might not space them. But that is for small conduits and not many conductors in the conduit.
> 
> Unless the conduits are large, the spacing is usualy maintained with scrap PVC conduit of the same size. Sometimes these conduits are stacked using the same method.
> 
> ...


So we are complaining about the rules...correct?


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## cabletie (Feb 12, 2011)

[/quote]So we are complaining about the rules...correct?[/QUOTE]

No not complaining. Just curious how others handle underground work. In fact it won't change the way I do things around here. 

I know in ground pools are harder to heat than above ground pools because of the way the heat is absorbed into the ground, so why would conductors be any different? But still there are tables to space underground conduits for heat dissipation. 

A co worker of mine failed an underground service because the conduits were to deep. The inspector cited the code rule that the conductors had to be compensated for the different depth. I don't rember what the outcome was for being a foot to deep after the site was graded. Can't rember how manny parallel sets were in the service, or if they were on chairs. I think they were on chairs but not concrete encased. 

I will continue to maintain some kind of space between conduits.


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## macmikeman (Jan 23, 2007)

Another theoretical problem with no real world documentation of reasonable melt down attributed to the conditions. 

You oversize your overcorrect device and you will cause melting of insulation. Proven. 

You separate the neutrals in metal conduit runs and you can cause melting of insulation. Proven

You stuff unbelievable amounts of conductors into a conduit cause you are too lazy or cheap to run multiple runs, such that there is no possible way to get another wire packed into that sandwich you will cause melting of insulation. Proven.

Directed at any who give this a second thought- 
But one full raceway dimension separation on racks- not proven, not found, one more example of over reading of theory books, white papers and the like. Too much time on the hands. Get a life. go away


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