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Tech Stuff - Cable and Wiring FAQ

This FAQ deals with various topics relating to wiring of all kinds.

<dissolution>A number of the descriptions below mention TIA/EIA (or even EIA/TIA). EIA was the old Electronics Industry Association which was dissolved in February 2011. Responsibilities for all the cabling stuff was taken over by TIA. One day we'll get round to cleaning up the references. But don't hold your breath. </dissolution>

  1. Who sets the standards for wiring?
  2. Who sets the standards for LAN wiring?
  3. Who sets the RS232 standards?
  4. What is the difference between RS232 and V.24 (or V.28)?
  5. What is a EIA/TIA 574 (Hint: its got 9 pins)?
  6. What is category 5 (or Category 5e) cabling?.
  7. What is the difference between category 3, 4 etc?.
  8. Can I use silver satin cables for LAN cables?
  9. What is EIA/TIA 568A and 568B wiring?
  10. Can I use a DB25 connector for V.35 connections?
  11. Is there a difference between telephone wiring and LAN wiring?
  12. What is the difference between RS232 and RS232C?
  13. What is RS232D?
  14. What is an 8 Position Modular Connector and does it differ from an RJ45?
  15. Can I run a LAN and telephones on the same LAN cable?
  16. Do I have to connect all 8 wires of a LAN cable?
  17. Does it really matter which pairs I use for LAN wiring?
  18. What's the difference between 100base-T4 and 100base-TX?
  19. What cables should I use for RS232?

Who sets the standards for wiring

LAN Cable standards are set by TIA/EIA (Telecommunications Industry Association/Electronics Industries alliance) (or EIA/TIA depends on whose web site you are on) e.g. Category 5 (a.k.a cat5 cat5e etc.). LAN connections/pinouts are defined by IEEE 802.3u. Telephone wiring standards are defined by TIA/EIA (Universal Service Order Code) (e.g. RJ48)

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Who sets the standards for LAN wiring

LAN Cable standards are set by TIA/EIA (or EIA/TIA it depends on whose web site you are on as to which way round these initials are written!) e.g. Category 5 (a.k.a cat5 cat5e etc.). LAN connections/pinouts are defined by IEEE 802.3u.

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Who sets the RS232 standards

RS232 standards are defined by the EIA/TIA.

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What is the difference between RS232 and V.24 (or V.28)

Almost nothing. RS232 defines both the physical and electrical characteristics and is defined by the EIA/TIA. The ITU (International Telecommunications Union - formerly CCITT) defines the signal properties (names) in V.24 and the electrical properties in V.28.

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What is a EIA/TIA 574 (Hint: its got 9 pins)

The EIA/TIA use the term 574 for what we, mere mortals, call a DB9 (see pinout diagram)

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What is category 5 (or Category 5e or Category 6) cabling.

Category 5 UTP (Unshielded Twisted Pair) cable is defined by the EIA/TIA for use with 10 and 100 MB LANs (10baseT and 100baseT) as specification number EIA/TIA-568A. Category 5e is a slightly improved specification published as EIA/TIA-568A-A-5 . Category 6 is defined by EIA/TAI-568-B.2-1.

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What is the difference between category 3, 4 etc. cabling

The following table defines the properties of each currently defined cable type (as of July'200)

EIA/TIA Category Speed LAN 100M Support ISO Spec EIA/TIA Spec
Category 3 16Mhz 10Mbit/s 100Base-T4
Category 4 20Mhz 16Mbit/s 100Base-T4
Category 5 (5e) 100Mhz 100Mbit/s 100Base-TX ISO/IEC-11801 TIA/EIA-568-A-5
Category 6 250Mhz 100Mbit/s 100Base-TX ISO/IEC-11801 TIA/EIA-568-B.2-1

Additional categories are being developed for Gigabit Ethernet and beyond but as of this writing (Sept'2003) had not been approved as standards by EIA/TIA.

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Can I use silver satin cables for LAN cables?

No. Silver satin cable is used for telephone wiring and does not support the more stringent requirement (higher speeds) used in LAN cables. Yes, we know people do use Silver Satin cable for LANs in very quiet (electrically quiet) offices but it just needs a little extra electrical noise (a new PC could do it) and it may no longer work. If you do use Silver Satin cables for LAN you should replace them especially if you are having problems.

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What is EIA/TIA 568A and 568B wiring?

EIA/TIA 568A and 568B are two wiring methods used to indicate which colors are assigned to which pin of the modular jack (see diagrams)

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Can I use a DB25 connector for V.35 connections?

V.35 (which no longer exists as a ITU standard - replaced by V.10/V.11) was specified to use a 37 pin connector (the chunkiest in the world). Nowadays for high speed serial connections (that use the term V.35) most manufacturers use a DB25 connector but may use a non-standard pinout. Check with the manufacturer. Here is the EIA/TIA RS-530-A standard balanced connection pinout for the DB25.

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Is there a difference between telephone wiring and LAN wiring

Yes there is. Primarily to do with the way pairs are allocated in the cables (see our primer for an explanation). Almost all cable sold as telephony cable is rated Category 3 which means you need to use 4 pairs if use it for LAN wiring - in general its a BAD idea.

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What is the difference between RS232 and RS232C

RS232 defines the electrical and physical standard. RS232C indicates it is wired using a DB25 connector (pinout diagram) rather than a DB9 (TIA 574) or an RJ45 (oops.. should say 8 Position Modular Connector) (RS232D).

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What is RS232D

RS232D is the name for an RS232 connection wired using a RJ45 jack (see pinout diagram)

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What is an 8 Position Modular Connector and does it differ from a RJ45

An 8 Position Modular Connector is more commonly, but erroneously, called (certainly by we mere mortals) an RJ45 (see our primer on jacks etc.)

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Can I run a LAN and telephones on the same LAN cable.

Depends. If you are using 100Base-T4 standards - that is you want to use cat 3, 4 or 5 cables ALL 4 PAIRS (8 wires) ARE REQUIRED. If you are using 100Base-TX (category 5 or 5e cables only) or 10Base-T the wires numbered 4 and 5 (one pair) and 7 and 8 (another pair) (see diagram) are not used in normal LAN operation but should still be connected since some equipment may use them for special purposes (we use them for power-over-ethernet in special applications). The spare pairs can be used for telephony - each pair will carry a single analog line so a cat 5/5e cable can carry 1 LAN (10 or 100 MB) and two telephone lines. However you are taking a RISK that in the future some genius may invent a fantastic application for one or more of these pairs and you may have to re-wire. Whether you consider this a high or low risk is a personal decision.

When wiring an analog telephone line on a LAN cable the following notes may help:

  1. All the LAN cabling MUST be category 5, 5e or higher.
  2. A normal analog phone uses 2 wires or one pair.
  3. If you are installing the cable and there is no EXISTING telephone connection on this cable use either spare PAIR of wires blue/blue-white OR brown/brown-white for each analog line.
  4. If the cable has an EXISTING telephone wiring connection find the other end of the cable and confirm that it is using either the blue/blue-white or brown/brown-white if so proceed as per 3 above, if NOT move the wiring to use either of these spare pairs (failure to do this will leave you with non-standard LAN wiring which will only lead to confusion in the future).

Due to the number of requests we get you may also want to read these additional notes on the subject.

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Do I have to connect all 8 wires of a LAN cable.

If you are using 100Base-T4 standards - that is you want to use cat 3, 4 or 5 cables ALL 4 PAIRS (8 wires) ARE REQUIRED. If you are using 100Base-TX (category 5 or 5e cables only) or 10Base-T the wires numbered 4 and 5 (one pair) and 7 and 8 (another pair) (see diagram) are not used in normal LAN operation but should still be connected since some equipment may use them for special purposes (we use them for power-over-ethernet in certain applications). They can be used for other functions e.g. telephony see above. Beware: You are taking a RISK that in the future some genius may invent a fantastic application for one or more of these pairs and you may have to re-wire. Whether you consider this a high or low risk is a personal decision.

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Does it really matter which pairs I use.

Technically No. BUT you will end up with non standard wiring. This might not seem important in the rush to fix to-day's problem but in six months time when you come to do some more work and cannot for the life of you remember your non-standard kluge you may think differently about standards. Standards are not a straight-jacket - they are there to give you the freedom to forget the problem. Ignore them at your peril.

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What's the difference between 100base-T4 and 100base-TX.

100base-T4 wiring uses all 4 pairs (8 wires) and allows for the use of Cat 3, Cat 4 OR Cat 5(e) cables. If you have ANY Cat 3 or Cat 4 cabling in your network you MUST use this standard. Most telephony cables (including 25, 50 or 100 pairs) are rated Cat 3. If your LAN uses these cables ANYWHERE you must use 100base-T4 wiring (see diagram). 100base-TX wiring uses only 2 pairs (4 wires or conductors) but can only be used with Cat 5, Cat 5e or higher cables.

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What cables should I use for RS232?

Somewhat sneakily the RS232 standards omit definition of a cable standard. Some folks use category 3 telephony cable which tends to come in 4-pair, 12-pair, 25-pair and 50-pair sizes so can be a tad overkill (or underkill). Alternatively, many manufacturers supply multi-conductor bulk cables which come with a variety of conductor numbers (3, 4, 8, 9, 10, 15, 20, 25 etc.). In general each connector is 24 AWG (though 26 AWG and 28 AWG are also available). Both shielded and un-shielded types are usually provided as well as solid and stranded conductors. All very confusing.

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