The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →A 50-pin Telco connector is a compact, 50-contact connector commonly used to connect multiple telephone or PBX circuits through one cable. In a common 25-pair telephone arrangement, pins 1–25 carry ring connections and pins 26–50 carry the matching tip connections. The name is also associated with RJ-21/RJ21X and “Amphenol-type” wiring, but the connector’s appearance alone does not guarantee a particular pinout.
What the name means
“50-pin Telco” usually refers to a miniature 50-contact ribbon-style connector used for multi-circuit telephone connections. Catalogs and equipment documentation may also call it an RJ-21 or RJ21X connector, or use “Amphenol-type” as a descriptive label. Legrand AV/C2G lists these alternate terms in its specialty connector guide.
As an Amazon Associate I earn from qualifying purchases.
It is a physical connector form, not a universal promise about what every contact does. A 50-contact connector may be used in different equipment or wiring arrangements, so verify the target device’s documentation before connecting a cable.
How the common 25-pair telephone pinout works
In the cited telephone arrangement, the 50 contacts form 25 tip-and-ring pairs. The Leviton catalog identifies ring contacts in positions 1 through 25 and their corresponding tip contacts in positions 26 through 50:
#1 Best Overall
- IDC TERMINATION: Uses insulation displacement connectors (IDC) to terminate 25 pairs of wires onto 25 polarized pins, ensuring secure and stable mechanical connections.
- SECURE CONNECTIONS: Features two 50-pin IDC telco connectors (RJ21) with high-strength copper alloy contacts, plated with 30 micro-inches of gold over nickel for reliable signal transmission.
- NATIONAL ELECTRICAL CODE (NEC) COMPLIANT: Built with 100% annealed solid bare copper conductors, meeting NEC Section 800.179, which mandates that "Conductors in communications cables, other than coaxial, shall be copper." Rated for 75°C and 300V, ICC cables ensure stable network communications while reducing fire hazards.
- 90-DEGREE CONNECTORS: Equipped with 90-degree 50-pin male and female telco connectors (RJ21) in a standard CN50 form factor, featuring protective hoods for secure connections in compact spaces.
- UL LISTED: Certified under UL listing E125268 and CMR riser-rated for flame resistance, allowing installation in vertical cable runs between floors.
| Telephone pair | Ring contact | Tip contact |
|---|---|---|
| 1 | 1 | 26 |
| 2 | 2 | 27 |
| 3 | 3 | 28 |
| … | … | … |
| 25 | 25 | 50 |
This arrangement is described in the Leviton catalog’s Wire Color Codes & Connector Pin Designations. Cisco’s VG310/VG320 voice gateway documentation gives the same starting pattern for its RJ-21 50-pin Amphenol cable: pair 1 uses ring pin 1 and tip pin 26, with subsequent pairs following sequentially. That is an equipment-specific example, not a guarantee that every 50-pin cable follows this wiring.
Does ISO/IEC 13575 define every Telco connector?
No. ISO/IEC 13575:1995 specifies mating dimensions and contact-number assignments for a 50-pole connector at a DTE/DCE interface. Its abstract says it “specifies a 50-pole connector, including the necessary mateability dimensions and the assignment of contact numbers, for use at the interface between data terminal equipment (DTE) and data circuit terminating equipment (DCE).” Its functional and electrical characteristics refer to other standards; its scope should not be treated as a universal RJ21X telephone wiring specification.
Rank #2
- IDC TERMINATION: Uses insulation displacement connectors (IDC) to terminate 25 pairs of wires onto 25 polarized pins, ensuring secure and stable mechanical connections.
- SECURE CONNECTIONS: Features two 50-pin male IDC telco connectors (RJ21) with high-strength copper alloy contacts, plated with 30 micro-inches of gold over nickel for reliable signal transmission.
- NATIONAL ELECTRICAL CODE (NEC) COMPLIANT: Built with 100% annealed solid bare copper conductors, meeting NEC Section 800.179, which mandates that "Conductors in communications cables, other than coaxial, shall be copper." Rated for 75°C and 300V, ICC cables ensure stable network communications while reducing fire hazards.
- 90-DEGREE CONNECTORS: Equipped with dual 90-degree 50-pin male telco connectors (RJ21) in a standard CN50 form factor, featuring protective hoods for secure connections in compact installations.
- UL LISTED: Certified under UL listing E125268 and CMR riser-rated for flame resistance, allowing installation in vertical cable runs between floors.
ISO lists the standard as published in March 1995, last reviewed and confirmed in 2001, and current on its ISO/IEC 13575:1995 catalog page.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
What to check before using or buying a cable
Compatibility depends on more than the 50-contact count. Check the equipment manual and confirm:
Rank #3
- IDC TERMINATION: Uses insulation displacement connectors (IDC) to terminate 25 pairs of wires onto 25 polarized pins, ensuring secure and stable mechanical connections.
- SECURE CONNECTIONS: Features two 50-pin IDC telco connectors (RJ21) with high-strength copper alloy contacts, plated with 30 micro-inches of gold over nickel for reliable signal transmission.
- NATIONAL ELECTRICAL CODE (NEC) COMPLIANT: Built with 100% annealed solid bare copper conductors, meeting NEC Section 800.179, which mandates that "Conductors in communications cables, other than coaxial, shall be copper." Rated for 75°C and 300V, ICC cables ensure stable network communications while reducing fire hazards.
- 90-DEGREE CONNECTORS: Equipped with 90-degree 50-pin male and female telco connectors (RJ21) in a standard CN50 form factor, featuring protective hoods for secure connections in compact spaces.
- UL LISTED: Certified under UL listing E125268 and CMR riser-rated for flame resistance, allowing installation in vertical cable runs between floors.
- Pinout: Match the cable’s contact assignments to the device. Do not assume the 25-pair telephone arrangement applies to another product.
- Connector and gender: Confirm the mating form and whether the equipment requires a plug or socket.
- Purpose and termination: Check which circuits the cable is meant to carry and what connector or wiring appears at its far end.
- Physical requirements: Select a cable length and construction suitable for the installation.
Cisco’s VG310/VG320 wiring documentation is useful for that gateway’s RJ-21 connection, but it should not substitute for the documentation for other equipment. In installations distributing multiple voice circuits, a compatible patch panel or termination assembly may also be part of the setup.
Quick Recap
Best Value
- Female, 50-pin RJ-21 connector
- 12 RJ11 jacks
- Double-sided foam tape
- Hold-down strap
- 50-pin male connector also available in storefront, or please inquire
Rank #4
- Produc Name : CN50 Connector;Interface Type : CN50 50 Pin Male
- Pin Pitch : 2.54mm
- Total Size : 77 x 16 x 21mm/3.1" x 0.63" x 0.83"(L*W*H)
- Weight : 26g
- Package Content : 1 x CN50 Connector
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
