underground wire seperation

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MBLES

Senior Member
i need to run 3-200a feeders underground going to seperate areas. if i use URD cable is there a distance seperation requirement. i found some literature on URD cable saying i need to keep 36' seperation. if i put in conduit i cant find anywhere where that is required at all. Any Code reference i can use to take the guess work out. i want to keep feeders together til i gotta separate feeder to there locations.
 

Tony S

Senior Member
I’ve been dealing with both MV and LV distribution for years. NEC codes and IET regulations aside, I can’t think of any practical reason why LV feeders should be separated.

If there is a reason, I’ve got a lot of digging to do to put things right.
 

iwire

Moderator
Staff member
Location
Massachusetts
Where 36" has come from I don't know

As he said, the note.

Figure 310.60 is the only thing I can come up with. The note indicates


Note: Minimum burial depths to top electrical ducts or cables shall be in accordance with 300.50. Maximum depth to the top of electrical duct banks shall be 750 mm (30 in.) and maximum depth to the top of direct buried cables shall be 900 mm (36 in.).
 

kwired

Electron manager
Location
NE Nebraska
i need to run 3-200a feeders underground going to seperate areas. if i use URD cable is there a distance seperation requirement. i found some literature on URD cable saying i need to keep 36' seperation. if i put in conduit i cant find anywhere where that is required at all. Any Code reference i can use to take the guess work out. i want to keep feeders together til i gotta separate feeder to there locations.


310.15(B)(3) is the NEC section that would come into play.

(3) Adjustment Factors.
More Than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a)^. Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

Direct buried in a trench, you can still arrange them to maintain spacing which helps allow them to dissipate any heat they produce, if you just throw them in all in close random proximity then you have something similar to having them all in one raceway and adjustment factors apply.

One advantage with URD is each "set" holds itself together where if yo were running individual direct bury conductors they are all loose and get mixed up easily.
 

Tony S

Senior Member
If you look at some of the manufactures tables for URD direct burial has a higher CCC than in ducts. I still can’t find anything resembling 36” spacing.


I’m sorry but this thread has got me intrigued.

The OP really needs to get back with the document he alluded to.
 

iwire

Moderator
Staff member
Location
Massachusetts
36” separation?

I did not say 36".


Magnetic repulsion under heavy fault conditions wouldn’t require that.

Ft = (0.17 x Ip²)/S

Where
Ft = Maximum Force per unit length of cable (N)
Ip= Peak short circuit current (KA)
S = Centre to centre distance between neighboring conductors (m)

https://www.youtube.com/watch?featu...nd the manufacturers literature on URD cable.
 

Tony S

Senior Member
I did not say 36".

It’s mentioned in the correction to the OP
24" is noted in 310-60


No one said it would but it sure gave someone a chance to strut. :p

Industrial power installations were my bread and butter for 20 years.


The note he mentioned and I posted is in the NEC table 310.60.

I don't know where he found the manufacturers literature on URD cable.

The OP didn’t, I did.

My comments.
 
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