TECHNOLOGY BRIEF

Channel Requirements and the Length of Stranded Cable

This technical brief describes how to substitute horizontal cable with patch cable while complying with industry standard channel requirements to ensure network performance.  This includes replacing the channel completely with patch cable.  This note applies to commercial and industrial installations. 

The ANSI/TIA 568 C.2 standard specifies the electrical parameters for Cat 5e, Cat 6 and Cat 6a structured cabling channels.  The maximum total length of these channels is 100m.  This is the worst case for insertion loss and delay.  As seen in the illustration below, the channel that is used to define category performance consists of 4 connectors, 90m of horizontal cable (solid conductor) and 10m of patch cable (flexible stranded conductor). 

This channel is also used by other standards groups to develop the performance requirements of network electronics.  Most installed channels are not configured to this standard or worst case channel.  Many installed channels have 2 or 3 connectors and have less than 90m of horizontal cable.  As the applications for Ethernet have increased beyond building installations, the variation or deviation from the standard channel has also increased.  In some applications, the channel is only a single cable with plugs.  Although this is not really structured cabling, network hardware intended to work on structured cabling channels will work in these channels provided the ANSI/TIA 568C.2 channel parameters are met. The channel requirements for industrial and commercial installations are the same. 

In channels, connectors are a factor in higher return loss and crosstalk resulting in more relaxed crosstalk and return loss requirements in comparison to bulk cable alone. This leaves delay and insertion loss as the limiting factors for cable length.  Delay will be met by keeping the total channel length less than or equal to 100m.  Insertion loss can be met by substituting the proper length of patch cable for the horizontal cable.  Stranded patch cable insertion loss is de-rated compared to horizontal cable insertion loss by 20% for 24 AWG and by 50% for 26 AWG.   It is important to note that standard channel insertion loss is based on 24 AWG patch cables for Cat 5e and Cat 6 and 26 AWG patch cables for Cat 6a. 26 AWG can be used in Cat 5e and Cat 6 and 24 AWG can be used in Cat 6a, but the cable lengths must be calculated differently. 

The three equations below can be used to calculate the mix of horizontal and patch cable that will produce a compliant channel: 

  1. For Cat 5e and Cat 6 channels and cable C=(102-H)/(1+D)    
  2. For Cat 6a channels and cable C=(105-H)/(1+D)          
  3. Applies to all channels T=H+C , T≤100m

Where:

  • H=Horizontal cable length
  • D=Patch cable de-rating by gauge (see table below)
  • C=Total patch cable length in channel
  • T=Total channel length

The table below are example calculations using equations 1,2 and 3.  The table is interactive and can be used to customize your specific calculations.            

In some installations, only stranded cable is used to simplify installations, reduce costs and maximize reliability by minimizing connections. This is shown in the above tables where the horizontal length, H, is zero.  In these cases the channel consists of 2 plugs and a length of cable.  In channel testing, the test interface is actually after the plug at the ends of the channel.  This means the plugs on the ends of a single cable used as a 2 plug channel will not be tested when using a handheld tester with channel adapters.  Quabbin®Wire & Cable recommends testing the channel as a patch cord assembly to verify that the connections are done properly.

Stranded Cable Calculations