Patch cords are the only part of generic cabling which are not in any way covered by the present issues of the established cabling standards ISO/IEC 11801, CENELEC EN 50173 or ANSI/TIA/EIA-568-A. No published official specifications for plugs or patch cords do so far exist although it has been realized that such specifications are necessary to fully specify and identify the connecting hardware. Intense work is presently going on in cabling committees to specify patch cords and RJ 45 plugs, but still the LAN owner has significant problems in selecting patch cords with known performance.

The following issues should be considered in connection with selection of patch cords:

Workmanship

Patch cords are generally prepared in large numbers in assembly lines with a significant amount of human handling. A major cause for functional failures and poor electrical performance comes from bad workmanship by the assemblers. Consequently samples from a delivery of patch cords should be visually inspected for evident failures (deformed plastics, deformed/misaligned contacts, improper moldings, contamination, etc. An inspection using 10X magnification would be beneficial and should prevent the majority of fatal problems.

Intermateability

The RJ 45 connector is not perfectly specified, neither with respect to contact dimensions nor screen construction. This means that there is a very small but actual risk that DC connection is not present when inserting a RJ 45 plug into a RJ 45 connecting hardware. Awareness about the problem, and possibly verification of performance with resistance measurements on actual connecting hardware on a sampling basis, should avoid fatal and expensive consequences of the problem.

Electrical Transmission Performance

Patch cords are not specified in ISO/IEC 11801, CENELEC EN 50173 and ANSI/TIA/EIA-568- A, but in all three standards it is implied that the NEXT performance (TOC NEXT) of the applied Cat. 5 plug termination should be from 40 dB to better than 41,5 dB.

TOC NEXT forms only part of the NEXT performance of patch cords and furthermore other parameters like far end crosstalk (FEXT) and return loss are very important for the patch cord performance, but are still not being specified. To make it even worse very many patch cords on the market have TOC NEXT below the min. specified 40 dB. Consequently it is not difficult to understand that everyone will be in an extremely difficult situation when performance of patch cords becomes critical for the future high speed transmission.

Standardisation is ongoing, but presently the only proposal for patch cord NEXT performance has been released by the TIA committee. This standard proposal only specifies one single performance rating, and therefore it is today not possible to non-destructively verify Cat. 5, Cat. 5+ and Cat. 6 patch cord performance.

Cats

Presently values for cable terminated RJ 45 plug performance are proposed by the TIA committee and are getting wide acceptance. This means that one can demonstrate Cat. 5, Cat. 5+ and Cat. 6 patch cord performance on a sampling basis using destructive, de-embedded NEXT measurements of the terminated plug, together with verification of general Cat. 5, Cat. 5+ and Cat. 6 patch cable performance.

Termination of Patch Cable Screens

As discussed for connecting hardware, the presence of a drain wire (in the patch cable) may tempt assemblers to make easy, but incorrect drain wire screen terminations leading to deterioration of EMC performance. This problem occurs if the patch cable screen is terminated to the RJ 45 plug screen through the drain wire, which is unfortunately commonly found for patch cords made from FTP cables. It is in fact not easy to make a high performance and inexpensive FTP screen termination, which explains why so very many bad FTP based patch cords exist.

The buyer of patch cords should assure that the EMC performance of patch cords is not evidently inferior by making a destructive inspection of the screen termination of one sample. The screen termination shall not be made through some, even down to a few millimetres, length of drain wire, but for instance directly through a long time stable pressure contact to the aluminum surface via the compressed drain wire.

The standardisation of patch cords is the subject of major attention, but is in an early stage. So far not one approved standard has ever been published, but drafts are now being prepared. Mature standards for patch cords and terminated (test) plugs must be developed as soon as possible, as the 2nd editions of ISO/IEC 11801, CENELEC EN 50173 and ANSI/TIA/EIA-568 can otherwise not be completed.

Due to the completely missing patch cords specification in all present generic cabling standards, the Cat. 5 patch cords are only becoming defined through the now developing standard proposals coming from TIA and the SC 48B Task Force. Two alternative test methods are presently available:

1. Non-destructive testing of complete patch cords using fixed test heads (jacks) with known performance. This method is simple to perform as a routine test, but does contain some influence of the terminating test heads. The performance of the terminating test heads is therefore specified to take into account and minimize this influence. Only one performance rating is presently specified (corresponding to Cat. 5).

2. Destructive testing of terminated RJ 45 plugs using the de-embedded test procedure. This test method can be used on a sampling basis to demonstrate Cat. 5, Cat. 5+ and Cat. 6 performance of the RJ 45 plug connection. When combined with performance verification of the patch cable the full patch cord can be verified as Cat. 5, Cat. 5+ or Cat. 6, but only on a sampling basis due to the destructive nature of the plug termination testing.

Standard proposals are still being discussed and only contain NEXT and FEXT requirements, while other important parameters, especially return loss, are not concluded.

3P has based the patch cord verification programme on the following measurement procedures:

• Visual inspection of contact section and moulding
• Wire map
• Screening performance, for instance as transfer impedance (for screened patch cord)
• Characteristic impedance (return loss), NEXT and FEXT of the applied patch cable
• De-embedded NEXT and FEXT of the cable terminated RJ 45 plug

Most of these test procedures are performed using normal electrical test specifications or common sense and experience. The de-embedded NEXT measurement is carried out according to TIA Interim "Additional Transmission performance specifications for 4-Pair 100 W Category 5 Connecting Hardware, Enhanced Category 5 Connecting Hardware and Category 6 Connecting Hardware".

Verification testing allows certification of all patch cord lengths based on testing of representative patch cord samples.

Basically the patch cord verification programme is a capability and component approval scheme, based on testing of components supplied to 3P. Consequently the validity of a certification will be limited as changes in the assembly line or components may occur over time. 3P has concluded that a reasonable validity period is 3 months which is therefore the offered period for re-testing.