CONCENTRIC NEUTRAL

[Alwayslearningelec]

I was trying to google the definition/use and this is what I found. A CN is only used on HV cable, is that correct.


System neutral to earth grounding, over the entire length of an electrical cable is achieved by adding one or more strips of semi-conductive material over the helically or otherwise wound concentric neutral conductors and completing the cable jacket with insulating material. The strip engages the soil when buried to provide a continuous ground path for the neutral conductors. In a second form protrusions of semi-conductive material project from a semi-conductive layer and encircle certain of the neutral conductors while the remainder are partially surrounded by the semi-conductive layer. Insulating material segments complete the cable jacket. The free ends of the protrusions engage the soil about the cable to provide a continuous ground for the neutral conductors helically wound or extending in parallel with the cable longitudinal axis.

 

[jumper]

I do not have a clue about HV cables, but most SEU cable has a CN.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet273

 

[mkgrady]

I was trying to google the definition/use and this is what I found. A CN is only used on HV cable, is that correct.


System neutral to earth grounding, over the entire length of an electrical cable is achieved by adding one or more strips of semi-conductive material over the helically or otherwise wound concentric neutral conductors and completing the cable jacket with insulating material. The strip engages the soil when buried to provide a continuous ground path for the neutral conductors. In a second form protrusions of semi-conductive material project from a semi-conductive layer and encircle certain of the neutral conductors while the remainder are partially surrounded by the semi-conductive layer. Insulating material segments complete the cable jacket. The free ends of the protrusions engage the soil about the cable to provide a continuous ground for the neutral conductors helically wound or extending in parallel with the cable longitudinal axis.

You have described medium voltage power cable and medium voltage concentric neutral power cable. On straight MV power cable the concentric wires (or foil tape) is not the neutral. It is a shield to drain the charge from the insulation in an even, uniform and predictable way. In a MV concentric neutral cable the outer wires perform the same task as above plus it serves as the neutral. That neutral may have a jacket over it or it may not. It is most often used in single phase MV distribution systems. A good example would be in an underground residential neighborhood.