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A 110 block is a type of punch block used to connect sets of wires in a structured cabling system. The "110" designation is also used to describe a type of insulation-displacement connector used to terminate twisted pair cables which uses a similar punch-down tool as the older 66 block. It is available in two varieties: pairwise connections, with each row containing two electrically connected terminals (the left two and the right two); and rowwise connections, with each row of four terminals all tied together. This option must be specified when ordering.
Early residential telephone systems used simple screw terminals to join cables to sockets in a tree topology. Since about 2000, these screw-terminal blocks have been slowly replaced by 110 blocks and sockets. Modern homes usually have phone service entering the house to a single 110 block, whence it is distributed by on-premises wiring to outlet boxes throughout the home in series or star topology. At the outlet box, cables are punched down to standard RJ-11 sockets, which fit in special faceplates.
In commercial settings, this style of "home run wiring" was already in use on 66 blocks in telecom closets and switchrooms. The 110 block has been slowly replacing the 66 block, especially for data communications usage.
The 110 block is often used at both ends of Category 5 cable runs through buildings, as shown in the image. In switch rooms, 110 blocks are used to connect cables to patch panels using devices called "chips". At the other end, 110 connections may be used with keystone modules that are attached wall plates. 110 blocks are preferred over 66 blocks in high-speed networks because they introduce less crosstalk and many are certified for use in Category 5 and Category 6 wiring systems, even Category 6a.
110 style blocks allow a much higher density of terminations in a given space than older style termination blocks (66 style or wire wrap). Some 110 blocks meet specifications for higher bandwidth data protocols such as Category 5 and higher.
During regular usage, small pieces of wire can become stuck inside the 110 block contacts; this renders that given pair unreliable or unusable, until the pieces are removed. A tool known as a spudger can be used to remove excess wire pieces.
A new wire inserted over an existing wire remnant will be unable to make reliable contact with the 110 block, which can handle only a single wire per contact. 110 blocks are also less reliable than 66 blocks for keeping cross connects in place.
For testing. it is more difficult to reliably connect to a working circuit on a 110 block than on older style blocks. The circuit must be broken, or insulation displacing contacts may be used on jumper wires. Repeated use of insulation displacing contacts may lead to a difficult to locate broken or intermittent jumper wire.
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