Telephone Jack Wiring Diagram: RJ11 Colour Code, Pin-Out & Installation

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A telephone jack wiring diagram shows how to connect the RJ11 modular connector to the correct colour-coded wires so that a single phone line delivers dial tone reliably. This guide covers the standard pin-out, colour codes for both US and UK wiring, and step-by-step installation.

The standard residential and small-business telephone jack is an RJ11 connector — a 6-position, 2-contact (6P2C) modular plug and socket. Despite having six physical positions, only the two centre pins (pins 3 and 4) are used for a single analogue telephone line.

Pin assignment and wire colours follow the T568 and FCC Part 68 standard in North America: - Pin 3 (Tip, Line 1): Green wire — the positive or 'tip' conductor of the phone line - Pin 4 (Ring, Line 1): Red wire — the negative or 'ring' conductor

The terms 'Tip' and 'Ring' come from the original telephone switchboard plug: the tip of the plug carried one conductor and the metal ring behind it carried the other. Tip is nominally at a slightly positive potential relative to Ring in the on-hook state, and the exchange applies ringing voltage (approximately 90V AC at 20 Hz in North America; approximately 75V AC at 25 Hz in the UK) across the pair to alert the telephone.

For a second telephone line (Line 2) on the same cable, pins 2 and 5 are used: - Pin 2 (Tip, Line 2): Black wire - Pin 5 (Ring, Line 2): Yellow wire

Pins 1 and 6 are not used in standard voice-grade telephone wiring.

In the United Kingdom, the historic BT wiring colour code differs significantly. A 6-wire British telephone cable uses: blue/white (A-wire, equivalent to Tip), orange/white (B-wire, equivalent to Ring), and other conductors for bell and auxiliary functions. The master socket on a British line includes a line-conditioning capacitor in the bell circuit.

The physical cable inside most homes is a flat or twisted 2-pair or 4-conductor cable sometimes called 'quad wire' or 'station cable.' The insulation colours follow the standard described above. Structured cabling installations may use Cat 3 or Cat 5e UTP cable with a different pair assignment.

RJ11 jacks are used for analogue voice, DSL broadband (which uses the same physical pair), and fax machines. DSL signals coexist on the same pair as voice using frequency division; microfilters installed at each jack prevent DSL interference on the voice circuit.

How to wire telephone jack wiring diagram

Test the line for voltage before working on it Use a non-contact voltage tester near the cable or a multimeter set to DC volts across the red and green wires. On-hook DC voltage is approximately 48V DC. Off-hook (telephone lifted) the voltage drops to 6–12V DC. Ringing voltage can reach 90V AC. Do not handle bare conductors while the line may receive a call.
Remove the old jack faceplate and identify the existing wires Unscrew the jack cover. The cable entering the back box will have at minimum a red and green pair (and in most cases yellow and black for Line 2). If the cable is older untwisted quad wire, the colour code is: green (Line 1 Tip), red (Line 1 Ring), black (Line 2 Tip), yellow (Line 2 Ring). If Cat 5e, match by pair: blue = Line 1 Ring, white/blue = Line 1 Tip.
Strip the cable outer jacket and individual insulation Strip approximately 30 mm (1.25 in) of outer jacket without nicking the inner conductors. Strip approximately 8 mm (0.3 in) of insulation from each conductor to be terminated. For screw-terminal jacks, form a clockwise hook in the conductor end. For IDC (insulation-displacement) jacks, no stripping is required — the IDC blade cuts through insulation when pressed.
Connect the wires to the correct terminals For a single-line jack: connect Green to the terminal marked Tip or L1T (pin 3), and Red to the terminal marked Ring or L1R (pin 4). For a two-line jack: additionally connect Black to L2T (pin 2) and Yellow to L2R (pin 5). On screw terminals, tighten clockwise until the conductor is firmly gripped without the wire breaking. On IDC terminals, press each conductor into the correct slot with a punchdown tool.
Fold and secure wiring, then reassemble the jack Fold the wires neatly into the back box so they do not strain the terminals. Clip or screw the faceplate back in place. If the back box is surface-mounted, ensure the cable entry is protected by a cable gland or grommet to prevent chafing.
Test the jack with a working telephone Plug a known-working analogue telephone into the jack. Lift the handset and listen for dial tone. If dial tone is present, the wiring is correct for Line 1. Dial a test number to confirm the connection is stable. For Line 2, use a two-line telephone or a line tester set to Line 2.

Specifications

Connector standard	RJ11 (6P2C) per FCC Part 68; two centre pins (pins 3 and 4) used for single line
Line 1 Tip wire colour (North America)	Green — connects to pin 3 of RJ11
Line 1 Ring wire colour (North America)	Red — connects to pin 4 of RJ11
On-hook DC line voltage	Approximately 48V DC (range: 42–56V DC depending on exchange equipment and line length)
Ringing voltage	Approximately 90V AC at 20 Hz (North America); approximately 75V AC at 25 Hz (UK)
Standard cable	24 AWG (0.5 mm²) solid copper, 2-pair or 4-conductor; Cat 3 or Cat 5e UTP for structured installations
Applicable standards	FCC Part 68 (USA); BS 6312, OFNL (UK); AS/ACIF S002 (Australia); ITU-T K.20

Safety warnings

Telephone lines carry DC on-hook voltage of approximately 48V and AC ringing voltage of approximately 90V AC at 20 Hz. While not normally lethal, the ringing voltage can cause a sharp shock and is a risk for people with pacemakers or cardiac conditions. Do not handle bare telephone conductors when a call may arrive.
Fixed telephone wiring in premises must comply with local telecommunications and building wiring regulations. In many jurisdictions, connection to the network demarcation point (the telephone company's equipment) is restricted to licensed telecommunications contractors.
Do not run telephone cable in the same conduit as mains power wiring. Maintain a minimum separation of 150 mm (6 in) from mains cables as specified in IEC 60364-4-44 and NEC Article 800 to prevent induction of mains frequency noise and to maintain insulation integrity.
When working near the main telephone entry point or DMARC (demarcation point), be aware that the line from the exchange is always live even if all internal telephones are disconnected. Use insulated tools and avoid bridging the Tip and Ring conductors.
Verify that any new wiring does not create a ground loop or connect the Tip or Ring conductor to earth ground. A Tip-to-earth connection will cause a permanent off-hook condition and prevent incoming calls.

Tools needed

Modular jack punchdown tool or flat-blade screwdriver for screw terminals
Wire strippers suitable for 24 AWG (0.5 mm) conductor
Multimeter with DC and AC voltage functions (to verify on-hook voltage and confirm correct termination)
RJ11 telephone line tester (optional but highly recommended — verifies polarity and line voltage at each outlet)
Cable staple gun or low-voltage cable clips
Drill and wall anchors for back box installation
Permanent marker for cable labelling at both ends

Common mistakes

Reversing the Red and Green wires (swapping Tip and Ring) — the telephone will usually still ring and receive calls because most phones tolerate reversed polarity, but some equipment (DSL modems, fax machines, older phones) will not operate correctly.
Leaving excess bare conductor exposed at screw terminals — this can cause a Tip-to-Ring short if the conductors touch, resulting in an off-hook condition and no dial tone.
Not installing DSL microfilters on all analogue devices sharing a DSL line — the result is loud noise on voice calls and reduced DSL sync speed.
Using solid-core conductor with modular plugs designed for stranded wire — solid conductors have a different deflection characteristic and may not make reliable contact with plug blades over time.
Failing to test polarity after installation — reversed polarity is not always obvious during basic handset testing but will cause problems with equipment that relies on correct Tip/Ring polarity.

Troubleshooting

No dial tone at the jack: Cause: Open circuit in wiring — broken conductor, loose terminal connection, or wrong wires connected to the jack Fix: Test voltage at the incoming cable before the jack (should read approximately 48V DC, Green positive to Red). If voltage is present at the cable but absent at the jack output, the fault is in the jack termination. Re-seat or re-terminate the wires. If voltage is absent at the cable end, the fault is upstream in the distribution wiring or at the network demarcation point.
Loud hum or noise on the line: Cause: Telephone cable running parallel to or in contact with mains power wiring; unbalanced pair due to wrong wire gauge or damaged insulation Fix: Reroute telephone cable away from mains wiring. Use twisted-pair cable (Cat 3 or Cat 5e) instead of flat untwisted quad wire in areas with high electromagnetic interference. Check for any points where the cable insulation is damaged and the conductor is touching a grounded surface.
Telephone rings but there is no dial tone or voice when answered: Cause: Tip and Ring reversed at the jack, or one conductor is connected and the other is open Fix: Measure DC voltage at the jack with no phone connected — Green should be positive relative to Red (approximately 48V DC). If Red is positive, Tip and Ring are swapped; swap the two wires at the jack terminal. If voltage is correct but there is no audio, there is likely a break in only one conductor — test continuity of each wire individually.

Frequently asked questions

Which wires are Tip and Ring on a standard US RJ11 telephone jack?

In the US standard, Tip (the positive or Line 1 positive conductor) is the green wire connected to pin 3 of the RJ11. Ring (the negative conductor) is the red wire connected to pin 4. These two centre pins are the only ones used for a basic single-line telephone connection.

Why do I get ringing voltage on the telephone line and is it dangerous?

The telephone exchange applies approximately 48V DC on-hook and superimposes a 90V AC ringing signal at 20 Hz to alert the telephone. The ringing voltage can cause an uncomfortable shock and is potentially dangerous to individuals with cardiac conditions. Always treat telephone wiring as live and avoid touching the red and green conductors when a call may be incoming.

What is the difference between an RJ11 and an RJ12 connector?

Both use the same 6-position (6P) body. RJ11 is a 6P2C connector using only the two centre pins for one telephone line. RJ12 is a 6P6C connector that uses all six pins and is used for two-line telephone sets or legacy key telephone systems. The physical housings are identical and will mate with each other.

Can I use Cat 5e cable for telephone wiring?

Yes. Cat 5e cable contains four twisted pairs and can carry up to four telephone lines. Convention assigns blue/white-blue to Line 1 (Tip/Ring), orange/white-orange to Line 2. The cable's performance far exceeds the requirements of analogue voice, and the twisting of pairs provides better noise rejection than older flat quad wire.

What wires are needed for DSL to work on the same line as voice?

DSL and voice share the same red and green (Tip and Ring) pair. No additional wiring is required. However, a DSL microfilter must be inserted between each analogue telephone or fax and the wall jack. The microfilter passes voice frequencies (300 Hz–3.4 kHz) to the phone and blocks the DSL frequencies, preventing interference.

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