Single conductor cable spacing

[olank]

Can anyone tell me the answer to this question. I have a product that I sell called KOZ cable blocks. These blocks are used to secure power cables. I have been told that when a single conductor cable is layed beside another single condustor cable that it must have a one cable spacing between them. Is this one cable spacing the outside diameter of the cable or the outside diameter of the conductor only? I am getting both answers from the industry. It would make sense that the answer is the outside siameter of the conductr (copper) as there are many different jackets available and they all have different diameters and characteristics. If anyone is interested in picturs of what I mean see

http://www.jms-supply.com.

Regards

Ken olan

 

[dpc]

NEC Article 392.11.A.3 -

Multi-conductor cables installed in a single layer in uncovered cable trays **with a maintained space of not less than one CABLE diameter** between cables.....

This means the cable O.D.


Similar rules exist for single-conductor cables, but the wording in the NEC is a little fuzzy. I think the intent of the requirement is the same, but the NEC says "not less than one cable diameter between individual **conductors**. This may be source of the differing opinions.

 

[busbar]

It's likely most authorities having jurisdiction (inspectors) would consider a cable diameter to be the more conservative ‘over the jacket’ dimension.

For ANSI regions, NEC Chapter 9 fill calculations use the verbiage “total cross-sectional area including insulation” and the qualifier “Where bare conductors are permitted…the dimensions for bare conductors…shall be permitted.”

It is an interesting question.

 

[tulum]

What is the reason for spacing paralleled conductors? Mutual inducatance?

 

[jghrist]

tulum,

The spacing allows air circulation around the cables and reduces mutual heating.

 

[gordonl]

Because the intent of the rule is to allow adequate spacing for cable cooling, I believe the it is the OD of entire the cable that is the measuring standard. Using conductor size to dictate spacing would have the opposite affect as required, the increased insulation thickness creates more "thermal" insulation to air, creating the need for more air circulation to compensate not less.