Medium voltage cable

[faresos]

Is there any advantage by using three conductor cable over using three single conductor cable (or the other way around) for medium voltage cables?

Thanks in advance..

 

[celtic]

The cross-sectional area may be smaller with a multi-conductor....resulting in:
- smaller conduit size ~ saves money.

The multi-conductor will require 1 pull vs. 3 for single conductors - saves money.

The termination/splice points might be a bit tricky - but only for those inexperienced with terminating/splicing a multi.

 

[faresos]

Thanks for your respond...

I have one more question, would that consider the three conductor cable to be one conductor (which will required 53% filling instead 40% filling for the three single conductors)? thanks again

 

[jtester]

There are equally as many downsides to 3 conductor cable. Are you serving predominately 3 phase loads? If not, single conductor cable has many benefits. How large a wire size do you need? You will have many more limitations if you need 500 kcmil for example.

What is your application?

Jim T

 

[wirenut1980]

Thanks for your respond...

I have one more question, would that consider the three conductor cable to be one conductor (which will required 53% filling instead 40% filling for the three single conductors)? thanks again

See the beginning of Chapter 9 in the NEC (I am using 2005 edition). Note 9 to the table states in part:

"A multiconductor cable of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area."

This surprised me when I looked it up. Intuitively I would have thought that you would still count a multiconductor cable as multiple conductors, since you still have 3 conductors.

Edit to add: Treating it as one conductor helps you in that it raises the maximum conduit fill allowed from 40% to 53%. You make it sound like a bad thing!

 

[wanderer20001us]

Mulitconductor cables are built as a system.

The multiconductor cable is not prone to cable role and binding during pulls, hence the 53% fill.

 

[ramsy]

Cable has another advantage not mentioned yet.

With concentric designs most common to HV & MV cables, I believe skin effect and perhaps XL is reduced more reliably. I see how surface-area ratios remove proximity / skin effects, but not sure how that dissipates heat or EMF more reliably than solid-core wires, with identical circular mills, or mm^2 conductor area. Trouble is, outside linemen are the only one's I've seen equipped to terminate concentric cables.