EN 50173 Specification  

EN 50173

EN 50173 is the principle design standard for structured cabling systems installed within the countries of the European Union.

Information technology Generic cabling systems August 1995
Amendment A1 January 2000

Amendment 1 adds various technical parameters to EN 50173 to make it suitable for gigabit LAN applications.

Related standards:-

EN 50174 Information technology – cabling installation
EN 50289 Communications cables – specifications for test methods
IEC/CISPR 22:1997 Limits and methods of measurement of radio interference characteristics of information technology equipment
EN 55024 Information technology equipment – immunity characteristics, limits and methods of measurement
IEC 60603-7 Connectors for frequencies below 3 MHz …8 way..connector  (this is the ‘RJ45’)
IEC 61935 Generic specification for the testing of balanced generic cabling in accordance with ISO/IEC 11801

It is expected that this first edition of EN 50173 with its amendment will be published again in 2001 as EN 50173 2nd edition, containing references to Class E/Cat 6 and Class F/Cat 7 operation.  A new cable standard, EN 50288 ‘Multi-element metallic cables used in analogue and digital communications and control,’ will also be invoked.

EN 50173 describes an hierarchical star cabling system with 90 m horizontal cabling and up to 2000 m of backbone cabling, split into 500m of building backbone and 1500m of campus backbone cabling.

EN 50173 describes channels and permanent links. 

The Permanent Link is the Telecommunications Outlet, TO (the wall or floor outlet), the (up to 90 m ) of horizontal cabling and the Floor Distributor, FD (the patch panel).  An optional Transition Point, TP, is allowed within the 90 m of horizontal cable.

The Channel is the work area cable (patchlead) form the terminal equipment into the TO, the permanent link as already described, a patchcord linking two patchpanels and a final equipment cable into the LAN equipment.  It is not compulsory to have two patchpanels (a cross connect), indeed most users use only one patchpanel (an interconnect).

Note that in the interconnect version, i.e. just one patch panel, the combined length of the patch cords A & C is 10 m.  In the cross connect model, i.e. two patch panels, the combined length of the patchcords A, B & C is 9 m.  EN 50173 and ISO 11801 allow for 50% more attenuation in patchcords (flexible cables) than for the fixed, solid core cable.  This is one major difference between ISO and EN standards and the American standard TIA 568A.  568A only allows for 20% more attenuation in flexible cables.  The 20% attenuation generally means that a 24 AWG patchcord is required.  For EN 50173 and ISO 11801 standards a patchcord can be implemented in 26 or 24 AWG, with 26 AWG being the cheaper of the two.

For horizontal cabling, the following cables are recommended:-

-100 ohm balanced copper cable

-62.5/125 multimode optical fibre


Recognised alternatives are 120 and 150 ohm balanced cables and 50/125 multimode optical fibre.

For backbone cabling, the following cables are allowed:-

-100 or 120 ohm balanced copper cable

-50/125, 62.5/125 or singlemode optical fibre

The end user must decide whether screened or unscreened cable is required and what level of fire performance is required, e.g. IEC 332-1, IEC 332-3-c etc.

Other ‘rules’ are:-

No more than two levels of cross-connect in the backbone.  This allows a Floor Distributor between the horizontal and building backbone cable, and a Building Distributor between the building and campus backbone cables, with all campus cables terminating in the Campus Distributor.

A minimum of one Floor Distributor for every 1000 square metres of office space.  A minimum of one Floor Distributor for every floor should be provided.  For a sparsely populated floor then it is permissible to serve this floor from an adjacent floor.

A minimum of one Telecommunication Outlet shall be provided at each work area.  A minimum of two TOs per ten square metres of floor space is advised.

The following Permanent Link/Channel Classes are described:-

Class A          specified up to 100 kHz

Class B          specified up to 1 MHz

Class C          specified up to 16 MHz

Class D          specified up to 100 MHz

Different channel lengths are achievable with different classes of cabling

Class of Application

Class A

Class B

Class C

Class D

Frequency range

100 kHz

1 MHz

16 MHz

100 MHz

Max distance with Cat3 Cable





Max distance with Cat5 Cable





The Standard describes the following technical parameters:-

Return Loss



Power Sum NEXT*

Attenuation to Crosstalk Ratio, ACR

Power Sum ACR*

Equal Level Far End Crosstalk, ELFEXT*

Power Sum ELFEXT*

DC Loop Resistance

Propagation Delay

Delay Skew*

Longitudinal to differential conversion loss

figures marked with * are new and added by Amendment A.

For the most part, all parameters are given values for both Permanent Link and Channel requirements, over the frequency range of interest.  For example, ACR;


Minimum ACR dB

Frequency Mhz

Permant Link Class D

Channel Class D

























Optical fibre grades have already been mentioned.  The multimode fibre performance is; 

Wavelength nm

Max. attenuation

dB/Km at 20oC

Min. modal bandwidth

MHz/Km at 20oC







Singlemode fibre is specified as having an attenuation of 1 dB/km or less at 1310 and 1550 nm

The SC duplex connector is specified for new installations although the STII connector (referred to in the Standard as BFOC/2.5) is allowed. 

Additional Information:  The new test standard referred to is IEC 61935.  The following tests are required as on-site acceptance tests.  Either the channel or permanent link may be tested.  Remember the permanent link is also called the Basic Link when two 2-metre patch cords are added to connect the test instrument. 


IEC 61935

   Wire Map




   NEXT pair to pair


   NEXT Powersum


   ELFEXT pair to pair


   ELFEXT Powersum


   Return Loss


   Propagation Delay


   Delay Skew


   DC Loop Resistance



The above information is offered as a summary of EN 50173 and Amendment 1.  It is not a definitive design guide and does not replace study and implementation of the Standard itself.  The publisher accepts no responsibility for inaccuracies or omissions.  To purchase the full Standard go to your national standards body, e.g. British Standards Institution, Nederlands Normalisatie Instituut etc. or CENELEC   

  Copyright Ó annor Ltd   2004