Last week, we looked at the 66 block, the most common type of connector block used as the demarc in business telephony installations. The punch down, insulation-displacing contacts of this device were a major innovation that improved time to install and the quality of the electrical contact between the wire conductor and the terminal. However, there can be challenges with physical placement of larger capacity cables run to 66 blocks, and most manufacturers’ 66 blocks do not meet the standards for terminating CAT-5 and higher cables. The 110 block solves these problems with an improved design for both the connector base and the punch-down terminals.

The 110 block was originally created as a cross-connect point in larger telephony installations. Typically, it is found in wiring closets located in hallways or within a tenant’s office suite on each floor of a building. Most often, these closets are intermediate cross-connect points between vertical (backbone) cable and horizontal cable going to workstation locations. As CAT-5 and above wiring systems came into use, however, several contractors began using 110 blocks at building entrances as network demarc points, rather than the 66 block.

Physically, the 110 block is a two-piece assembly consisting of a raised wiring block that forms a base and several much smaller connecting blocks that fit on top of groups of terminals on the base. Wiring blocks are available in 25, 50, 75, 100, and 300 wire pair capacities, arranged in 25-pair rows. Each row consists of 50 individual wire channels, where each wire of a pair is laid. The wiring block is a raised frame that has sufficient rear clearance to allow riser or other cables to be brought in from underneath the block to the right or left edge. At the edge, cable jackets are removed, and wire pairs are routed through trough-like wire channels on the top of the block, slightly lower and directly next to the rows of individual wire channels. The small columns that form each side of the individual wire channel are color-coded for easy identification of pair groups.

Connector blocks are the devices that both make the electrical connection and mechanically secure the pairs to the wiring block. Embedded in both top and bottom of the connector blocks are metal insulation-displacing termination knives similar to, but much smaller than, the terminals on a 66 block. When a special impact tool secures the 110 connector block on top of a group of pairs in a row of the 110 wiring block, the termination knives cut the insulation at each contact point, making electrical contact between the pair from the cable and the termination knife. Pairs from workstations may then be placed in channels on top of the connector block and connected to the termination knife using an impact tool.

Connector blocks are available in three-, four- or five-pair capacities. Typically, four-pair connector blocks are used to terminate six four-pair cables brought into the wiring block channel, three per side of the block. Since the connector block has a 25-pair capacity per row, the rightmost position in each row is usually vacant, and the rightmost connector block may be a five-pair version.

Once a connector block is attached, it is very difficult to remove. Most wiring changes are done by removing and reattaching pairs at the top of a connector block that is already attached to a wiring block.

In a finished installation, the larger wire channels across the length of the 110 block are covered by label strips that identify the pairs going to workstations.

– Justin J. Junkus

The Daily



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