Resource for Sizing ducts for power cables and inner ducts 1

[larrym]

Any suggestions for properly sizing HDPE conduits for 4/0 power conductors for a 2200 ft conduit run and sizing an outer conduit to nest three power conduits into?

Regards
Larry


Larry Mackey

 

[waross]

NEC National Electrical Code.
CEC Canadian electrical code.
Look at the appropriate tables.

Maximum conduit and tubing fill, Percentage by area:
[tt]Number of conductors or multi-conductor cables -------------- 1 -- 2 -- 3 - 4 -- Over 4
Conductors or multi-conductor cables (not lead-sheathed)----- 53%--31%--40%-40% ---- 40%
Lead-sheathed conductor or multi-conductor cables ----------- 55%--30%--40%--38% --- 35%[/tt]
(CEC)
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

I'm not sure you can follow any standard that recommends the ampacity of a running cable in a duct while this duct is running in another duct.
I think you have to calculate the ampacity following Neher&McGrath theory[IEEE 835/1994] or IEC 60287.
You have to calculate temperature drops from conductor through insulation and jacket and from cable surface to inner conduit and from conduit surface to outer pipe and eventually the temperature drop from outer pipe to ambient .
You need the insulation, jacket, conduit, pipe and ambient thermal resistance. I don't know if ETAP software could calculate it however I'm sure some software programs are capable of doing it.

 

[7anoter4]

On the other hand if you need only the conduit size then take the 4/0 XHHN cable from NEC 2017 chapter 9 Tb. 5 [0.638 " and 0.3197 inch^2 area] for 40% [as waross said] 3 cable of total 3*0.3197=0.9591 inch^2.From :
Articles 352 and 353 — Rigid PVC Conduit (PVC), Schedule 40, and HDPE Conduit (HDPE)
table- in the same chapter 9- only 2" it is close [1.316 inch^2 for 40% permissible].
The enveloping pipe inside diameter has to be 2.16*conduit 2" outside diameter =2.375" then 2.16*2.375=5.13". 5" pipe inside diameter is 5.047".So you need 6"-in my opinion.

 

[waross]

You may want to add a little for staggered couplings. For aligned couplings add a little more.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[7anoter4]

Thank you, waross. I forgot the couplings.I think it is possible to arrange them staggered always.