Telephone Wiring

17 Mar

FREQUENTLY ASKED QUESTIONS (most with answers)
Maintained by: Jonathan Johnson mailto:webmoth@webmoth.com
Archived at: http://www.teleport.com/~skipj/telefaq.html
Edition: 1.1 (16 May 1998)

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Section 0: Definitions

0.00: What is the purpose of this FAQ?
0.01: What is a telephone?
0.02: What is pulse/tone?
Section 1: Equipment
1.01: What jack types are available?
1.02: What is meant by RJ11/RJ14/RJ45 in jack types?
Section 2: Wires and color codes
2.01: What is the proper type of wire to use?
2.02: What does twisting have to do with anything?
2.03: What are the color codes for line 1/2/3/4/etc.?
2.04: What special considerations should I have for modem use?
Section 3: Voltages
3.01: What is ring/tip/sleeve?
3.02: What voltages are expected on the line
Section 4: Theory and Operation
4.01: How does a telephone dial?
4.02: Who invented the pulse-dial system?
4.03: My stereo has 3,658.9 wires. How does the telephone get by withonly two?
4.04: Why do telephones sound so cruddy (no bass/no highs)?
Section 5: Cordless telephones
5.01: Why is this section here?
Section 6: Further Information
6.01: Where can I get more information?
Section 7: Maintaining this FAQ
7.01: You really screwed up. How do I flame you?

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SECTION 0: DEFINITIONS

0.00: What is the purpose of this FAQ?
A: To educate and inform. This FAQ deals with standard analog telephonewiring only. It does not pretend to deal with any other telephone system,such as ISDN. Entertainment included at no extra charge to you (unlessyou’re on CompuSteal, America OnLose, or Progeny and are paying mucho-bucksper hour and I am wasting your time).

0.01: What is a telephone?
A: A telephone is a device which allows people to communicate by voiceover great distances at relatively inexpensive cost (compared to a planeticket). If Alexander Graham Bell had invented it today, it would be calleda “Vocal communications network access terminal (VC-NAT).”

0.02: What is pulse/tone?
A: “Pulse” and “tone” are two very different dialing protocols. Mosttelephone networks are capable of handling either protocol; use tone ifpossible. For a more detailed explanation, see section 4.01, “How doesa telephone dial?”

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SECTION 1: Equipment
1.01: What jack types are available?
A: There are several types, the most common being the “modular” style.Also is hard-wire, and four-prong.

1.02: What is meant by RJ11/RJ14/RJ45 in jack types?
A: These are types of modular jacks. RJ11 is a small, 4-position modularjack (like on the handset). RJ14 is a 6-position jack (usu. with 2 or 4wires) such as the line cord. RJ45 is an 8-position jack, not often usedfor standard telephones, but is used for some “system” telephones and forEthernet (computer) wiring.

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SECTION 2: Wires and color codes
2.01: What is the proper type of wire to use?
A: Telephone wire must have the letters “CM” in its type rating. Telephonewire size is referred to in “pairs”– such as 2-pair (4-wire), 3-pair (6-wire),and so on. Wire smaller than 24 AWG should never be used.
Although it is available, 1- and 2-pair wire is not recommended, asit is usually not twisted, and should it fail, there are no extra pairsto fall back on.
6- or 8- pair is recommended. The wire should be CAT-2 or better. I highly recommend using CAT-5, as the price difference is minimal if youshop around for it.

2.02: What does twisting have to do with anything?
A: Twisting each _pair_ (not the whole cable) helps reduce signal lossand rejects interference. Also helps prevent “crosstalk” (where a signalbleeds from one pair to another). The tighter the twist, the clearer theline.
CAT-1 is not twisted at all, and CAT-2 is barely so. I recommend goingwith at least CAT-3 4-pair wire, especially if you plan to use a modem.
If you’re really fanatical, you could do your telephone wiring withbalanced microphone cable (2 conductors plus shield). Just be sure youground the shield at the phone co. interface box ONLY (don’t connect itto the line wires).

2.03: What are the color codes for lines 1/2/3/4/etc.?
A: Note that a standard RJ14 jack has six positions and may have two,four, or six pins. There are two color codes, described below:

Pair: Ring (-): Tip (+)
—————————–
1 Red Green
2 Yellow Black
3 Blue White
—————————–
1 Blue/WH White/BU
2 Orange/WH White/OR
3 Green/WH White/GN
4 Brown/WH White/BN

There are additional colors for cables with more than 4 pairs, but Idon’t know what they are right now. When I find out I’ll include the listin an appendix.

As you look at the _jack_ from the “front”, with the tab slot down,the pins are arranged as so:
4R-3T-2T-1R-1T-2R-3R-4T (eight pos.-eightpins RJ45)
3T-2T-1R-1T-2R-3R (six positions-six pins RJ14)
xx-2T-1R-1T-2R-xx (six positions-four pins RJ14)

The “white” may or may not have a color band corresponding to its partnercolor.

2.04: What special considerations should I have for modem use?
A: See also question 2.01. When using a modem, highest data transferrates can be achieved when external noise is reduced as much as possible.To reduce unwanted noise, consider the following:

Make cable runs as short as possible. Seriously consider using CAT-5 communicationscable (10BaseT ethernet cable).
Route cables as far away from other wiring (house wiring, doorbell, cableTV, etc) as practical. If the telephone wire must cross another wiringsystem, cross at a 90 degree angle. A telephone wire running parallel andnear to another wiring system can receive inductive interference (“crosstalk”)from that other wiring system, which will degrade modem performance.
Make sure you have plenty of Doritos and Coke available when you have yourcomputer guru (a 13-year-old kid, in most circumstances) pay you a visit.
Many of these same principles apply to ISDN (a high-speed, multiplexingtelephone line), which itself is beyond the scope of this FAQ.

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SECTION 3: Voltages

3.01: What is ring/tip/sleeve?
A: Look at the plug on the end of your stereo headphones (my apologiesif you are listening to your favorite CD). You will see something likethis:
____________
| |______________
========| TAIWAN |_________|_|__>
|____________| ^ ^ ^
S R T

This is known as a “Phone plug.” The telephone companies used these(1/4″ in diameter) in the patch bays that the operators used to usewhenconnecting you to “CHicago 17” or something like that. You will noticeit has a tip (T), a ring

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