Encased conduits

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genesparky

Member
Location
Kingman Az.
Is there a minimum requirement or suggestion for the distance between the spacers that hold conduit apart in concrete? We are installing 3 inch rigid.

Thanks for any help.
 

RUWired

Senior Member
Location
Pa.
genesparky said:
Is there a minimum requirement or suggestion for the distance between the spacers that hold conduit apart in concrete? .
A typical 3" base spacer is with a 3"seperation.That is enough to get the crete between the conduits.Specification will dictate otherwise.
 

genesparky

Member
Location
Kingman Az.
Thanks for the reply. What I am trying to determine is how far apart along the pipe do I place the spacers? Is it the same as strapping conduit above ground? Would I use table 344.30? I need to know how many to buy.

Thanks again for any help
Kevin
 

barclayd

Senior Member
Location
Colorado
I don't think I've ever seen a ductbank with concrete encased rigid.
We always use rigid sweeps (long-radius 90's) for the vertical transitions. We always tape the sweeps with pipe-wrap to minimize corrosion where it comes out of the concrete.
Why not use EB Duct? It has much larger cross-sectional area compared to the same trade size of rigid, and I think the pull would be easier.
Be sure to anchor the spacers to keep the conduits from floating ( might not be necessary with rigid ??)
I think I would be worried about corrosion - any thoughts??
 

iwire

Moderator
Staff member
Location
Massachusetts
lowryder88h said:
genesparky, If I understand your question, how far apart on the 10' stick of RMC, I usually figure two bases per 10'.

I agree, 5' is as far as I push it, the bases are so flimsy I might even tighten it up with rigid.
 

genesparky

Member
Location
Kingman Az.
barclayd said:
I don't think I've ever seen a ductbank with concrete encased rigid.
We always use rigid sweeps (long-radius 90's) for the vertical transitions. We always tape the sweeps with pipe-wrap to minimize corrosion where it comes out of the concrete.
Why not use EB Duct? It has much larger cross-sectional area compared to the same trade size of rigid, and I think the pull would be easier.
Be sure to anchor the spacers to keep the conduits from floating ( might not be necessary with rigid ??)
I think I would be worried about corrosion - any thoughts??
Actually we are running PVC coated Rigid. I would like to use duct, The engineer insists on steel. There will be large trucks in the area and he does not want to take a chance on crushing the run.
Thanks for the replys.
 

barclayd

Senior Member
Location
Colorado
I would do what iwire says and maybe plan on 3 sets of spacers per 10'. The manufacturer's recommendations are based on pvc, not rigid. Might even be worth a call to Underground Devices, or Carlon.
It ain't my money, but it sounds like the electrical engineer making structural decisions should put some added profit into your operation. Be aggressive in your bid.
Them must be some mighty big trucks.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
barclayd said:
Why not use EB Duct? It has much larger cross-sectional area compared to the same trade size of rigid, and I think the pull would be easier.
What is EB duct? I have never heard that term.
Don
 
barclayd said:
I would do what iwire says and maybe plan on 3 sets of spacers per 10'. The manufacturer's recommendations are based on pvc, not rigid. Might even be worth a call to Underground Devices, or Carlon.
It ain't my money, but it sounds like the electrical engineer making structural decisions should put some added profit into your operation. Be aggressive in your bid.
Them must be some mighty big trucks.

What you want to avoid is concrete pushing down on the conduit between supports so when you pull it is like pulling through a roller coaster, up-and-down-up-and-down......:D Look for the spacer manufacturers installation instructions.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
barclayd said:
EB Duct is a non-metallic conduit made expressly for concrete Encased ductbanks.
That is what I thought you were talking about. I don't believe you can use those products for a NEC installation.
Don
 

barclayd

Senior Member
Location
Colorado
don_resqcapt19 said:
That is what I thought you were talking about. I don't believe you can use those products for a NEC installation.
Don

The Carlon catalog contains this phrase:

ETL Listed
to UL 651A in
compliance
to the NEC

Plus a bunch of NEMA & ASTM Standards.

We've put in MILES of this stuff around the Denver Area.
Why would it not be compliant with Article 352?
db
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
barclayd,
The Carlon catalog contains this phrase:
ETL Listed
to UL 651A in
compliance
to the NEC
The UL standard for rigid nonmetallic conduit as covered by Article 352 is 651, not 651A. UL 651A is for rigid nonmetallic underground conduit. I find no reference to that product in the NEC. Note the white book info for 651A mentions use per Article 352, but I don't see any thing in the code that permits this product to be used in NEC applications. Also just because something is in compliance with NEMA and ASTM standards does not mean that it is compliant with the NEC.
Don
 
Last edited:

barclayd

Senior Member
Location
Colorado
UL 651 covers Sch 40 & Sch 80 PVC Conduit.
There is nothing in Article 352 that limits the definition of "Rigid Nonmetallic Conduit" to Sch 40 or Sch 80 PVC.
Article 352.6 Listing Requirements makes no mention of either UL651 or 651A.

This could be a glass half-empty half-full situation. You don't see anything that would permit it, and I don't see anything that would prohibit it.


slainte
db
 
iwire said:
:grin:

I can't imagine what truck will crush or break a properly installed duct bank.:-?

Some years ago I worked on the replacement of a manufacturing site's entire MV distribution system. It was a steel foundry with rail carying around the material.

Thousands of feet of 9/12/16 5-6" steel reinforced ductbanks between manholes. All lead covered. The old banks were progessively failing due to the road traffic, cables short out and can't even be pulled out as the conduits were no longer passable.
 
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