Modular Plug and Jack Types

NOTE:

We recommend adoption of 8P8C, 6P4C terminology when describing modular plugs and jacks. This is a definite way to avoid confusion between similar plugs.

The codes RJ11, RJ12, RJ45 and other RJ, Register Jack, numbers actually specify various wiring configurations used in the USA, not actual plug or jack types.

There are several modular jack sizes and variations.

4 Position

The 4 position modular plug (4P4C) is narrower then the 6 position modular plug. Usually used on coiled telephone handset cables, although occasionally used for other applications.

6 Position

The 6 position modular plug is mostly commonly used for cables in voice applications and is often referred to as RJ11 or RJ12. The 6 position poly-carbonate body can be loaded with only the centre 2 or 4 gold contacts or can be fully loaded with all 6 contacts. For basic 2 wire voice applications, the centre 2 contacts are used and the plug should be correctly described as 6P2C (6 position, 2 contact).

Where 4 wires are required in the UK to provide the ring tone. The centre 4 contacts are used and the plug should be correctly described as 6P4C.

In applications which require, all contacts loaded the plug is called 6P6C.

8 Position

The 8 position modular plug is now becoming the standard for data and voice applications. This jack is usually referred to as RJ45. The plug body is usually supplied will all 8 gold contacts loaded and should be correctly referred to as 8P8C. For basic voice connections only the centre 2 or 4 are required (8P2C or 8P4C).

For data applications, several colour coding sequences are used for the conductor pairs. In the UK, the mostly widely used system is known as T568A.

10 Position

The 10 position (10P10C) modular plug has the same body width as the 8 position but has an extra contact on each side.

MMP

The MMP - Modified Modular Plug is a proprietary variation of the 6 position plug which was developed by Digital Equipment Corporation (DEC). The MMP plug has the latch shifted from the centre to one side to avoid the possibility of interchanging DEC data wiring and a normal telephone line plug. MMP is also referred to as DEC-Connect or MMJ. An 8 position keyed modular.

Modular Plug Variations

Round or Flat Entry

Two variations of modular plug exist to accommodate either flat or round cable. The lower face of the cable entry on the rear of the plug body can be either flat or round.

The round type should always be used when terminating Cat5E or Cat6 or other round cables to ensure that the jacket and conductors are not crushed during termination. Flat cable plugs must be used to ensure adequate cable strain relief of flat cables.

Contacts for Solid or Stranded Conductors

The IDC (Insulation Displacement Contact) section of the gold contacts can be designed for either solid conductors or stranded conductors. Plugs for solid wires have a 3 pronged contact which forks over the solid conductor whilst the contacts for stranded conductors have 2 spikes which penetrate between the strands. Failure to use the correct contact type will result in unreliable terminations.

Modular Plug Termination Recommendations

• Always use a modular plug with the correct contacts for stranded conductors or solid conductors.
• Do not terminate flat cable plugs into round cable or vice versa.
• Avoid plugging 6 position plugs into 8 position sockets where possible.
• Use quality tools for crimping modular plugs.
• Avoid RJ11, RJ45 termination to avoid confusion.
• Ensure plugs with suitable grade of gold plating are used.
• Avoid excessive bending or squashing of the data cable jacket.
• Use plug boots to provide extra strain relief.

Modular Plug Gold Plating

The contacts used in modular plugs are gold plated and the gold plating thickness affects the electrical characteristics of the contact and it is resistance to corrosion. The thickness of the gold plating is usually measured in microns.