NX How is the NX Electrical Routing Bundle Diameter Calculated

How is the routing bundle diameter calculated? 
Why does the diameter of the bundle sometimes reduce when additional wires are included in the bundle?
Why is the diameter of the bundle sometimes less than the diameter of the largest wire?

Solution

When wires are assigned to a path in Electrical routing NX will calculate a diameter for this bundle of wires and this will be used to drive the diameter of the swept geometry on this path. 


The default calculation used by NX is intended to cover the most common situations and works best when there are many wires of roughly the same size. If there are a small number of wires and they are widely varying sizes the results are not as accurate. This document explains the calculation method and explains how this can lead to confusing results.


NX uses two main values for the calculation of the bundle diameter


1)      Average wire diameter
For example if there are 5 wires of diameters 10,9,8,7 and 6 then the average diameter would be 8mm
(10+9+8+7+6)/5=8
Note: When bundling cables or shields, only cable or shield children are used in determining the average wire diameter.


2)      Bundle Factor
This is a value applied to the bundle which varies depending on the number of wires in the bundle. The full list is defined in NASA Tech Brief MSC-16378. Some example values taken from this list are shown below.

 


Using the two values defined above the overall bundle diameter is calculated by multiplying them together, giving the following equation:


Bundle Diameter = Average wire Diameter * Bundle Factor


If filler stock is being used then there are some additional factors to the calculation.  This is described in detail in the NX help documentation under the heading "Understanding bundle diameter calculation".

Here are some examples of how the bundle calculation is performed, sometime leading to unexpected results.



Example 1 – Accurate result. Many wires of similar diameter
Bundle contains 10 wires of the following diameters -1,2,3,2,2.5,2,1,1.5, 1,3


Average Wire Diameter = 1.9
 Bundle Factor = 3.86
 Bundle Diameter = 7.334



Example 2 – Inaccurate result. Low number of wires and different diameters.
Bundle contains 3 wires of diameters 1,1 and 5


Average Wire Diameter = 2.333
 Bundle Factor = 2.11
 Bundle Diameter = 4.92
 The bundle diameter is calculated to be lower than the diameter of the largest wire!
 
Example 3 – Bundle Diameter reduces when two bundles join


Occasionally the bundle diameter calculation can lead to the confusing situation of the bundle diameter reducing when 2 separate bundles are joined together.  This could be when a bundle of small wires merges with a bundle of larger diameter wires


Bundle 1 contains 3 wires – 1,2,1.5
 Bundle Diameter = 1.5 * 2.11 = 3.165


Bundle 2 contains 3 wires – 8,6,7
 Bundle Diameter = 7 * 2.11 = 14.77


Bundle 3 is after the point where Bundles 1 and 2 join
 Average Wire Diameter = 4.25
 Bundle Factor = 2.99
 Bundle Diameter = 12.7075
 
 


In this example the bundle diameters would look something like this when viewed in Electrical Routing:

Hardware/Software Configuration

Platform: all
OS: n/a
OS Version: n/a
Product: NX
Application: ROUTING_ELEC
Version: V1953
Function: CONNECTION_LIST
Product: NX
Application: ROUTING_GENERAL
Version: V1953
Function: PATH

Ref: 002-8529970