Advantages of Biscuit Jacks

Biscuit jacks offer a few advantages in your structured-cabling design. First of all, they are very inexpensive compared to other types of surface-mount wiring systems, which is why many houses that had the old four-pin telephone systems now have biscuit jacks—you could buy 20 of them for around $25. Even the biscuits that support multiple jacks are still fairly inexpensive.

Another advantage of biscuit jacks is their ability to work in situations where standard modular or fixed-design wall plates won't work and other types of surface-mount wiring are too bulky. The best example of this is office cubicles (i.e., modular furniture). A biscuit jack has an adhesive tab on the back that allows it to be mounted anywhere, so you can run a telephone or data cable to a biscuit jack and mount it under the desk where it will be out of the way.

Finally, biscuit jacks are easy to install. The cover is removed with one screw. Inside many of the biscuit jacks are screw terminals (one per pin in each jack), as shown in Figure 1. To install the jack, you just strip the insulation from each conductor and wrap it clockwise around the terminal and between the washers and tighten the screw. Repeat this process for each conductor in the cable. These jacks are not high-speed data compatible and are capable of Category 3 performance at best.

 
Figure 1: Screw terminals inside a biscuit jack

Note

Not all biscuit jacks use screw terminals. The more modern data communications jacks use IDC connectors to attach the wire to the jack.

Disadvantages of Biscuit Jacks

The main disadvantage to biscuit jacks is that the older biscuit jacks are not rated for high-speed data communications. Notice the bunch of screw terminals in the biscuit jack shown in Figure 1. When a conductor is wrapped around these terminals, it is exposed to stray electromagnetic interference (EMI) and other interference, which reduces the effective ability of this type of jack to carry data. At most, the older biscuit jacks with the screw terminals can be rated as Category 3 and are not suitable for the 100Mbps and faster communications today's wiring systems must be able to carry.