Wiring Block Techniques and Tips

Important Wiring Block Concepts

One big advantage of using a block to connect telephone wiring is that it gives you a lot of options on how to configure the installation to meet your requirements. That makes it important to spend some time planning your installation for a configuration that best meets your current needs and allows for future requirements.

An important concept to understand when planning a block installation is that cables are attached to blocks as a “permanent” installation and signals are extended between cables using cross-connect jumper wires. The only “built in” electrical connectivity on a 66 block (specifically 66M1-50 blocks like those illustrated and offered for sale on this site) is between each outer punch lug and the inner punch lug next to it. The only “built in” electrical connectivity on a 110 block is between the top and bottom of each wire position of the c-clips. All connectivity between the cables attached to a block is established by installing cross-connect jumper wires. On 66 blocks, the cables are terminated on the outside row of punch lugs and cross-connects are made on the inner lugs. On 110 blocks, the cables are seated in the base of the block and held permanently in place using c-clips and cross-connects are made on the top of the c-clips. Beyond those concepts, how a block is configured is dictated by the particular installation.

Cables on a block are generally arranged in an order that corresponds to the flow of the signal:

  • Connections to the public network (e.g. cable from the NID)
  • Connections to central equipment (e.g. cable to a DSL splitter)
  • Connection to stations (e.g. inside wiring cables to jacks)
  • When practical, inside wiring cables are arranged in an order that corresponds to the location of the other end of the cable (e.g. by room or by floor)
  • On a 66 block, ease of using bridge clips and installing cross-connects, might dictate a particular configuration,such as installing the cables to the NID and a DSL splitter in the same rows on opposite sides of the block.

As little sheath as possible is removed from the cable and the twist of the pairs is preserved as much as possible. That will preserve the quality of the cable to reject interference. All pairs of cables are normally terminated, even if the current requirement only needs one or two pairs, because it would be impractical to re-terminate the cables if access to the other pairs was required in the future.

Both 66 and 110 blocks are equally suitable for telephone wiring. One is not really “better” than the other. Block type selection for telephone wiring is normally dictated by factors such as cost, pair capacity, available mounting space, matching block type with existing blocks, availability of tools, and preferences of the installer. When 110 blocks were first manufactured, they were preferred for data use, but newer 66 blocks maintain CAT5 or better standards when properly installed. Patch blocks/panels are now preferred for most data connections instead of standard wiring blocks, but when cables are to be used interchangeably for voice and data, use of wiring blocks is still a reliable practice.

Regardless of which block you decide on using, be sure to use the appropriate punchdown tool. Trying to use substitute tools such as pliers and screwdrivers will not create a reliable connection and can damage the block, preventing reliable connections even if an appropriate punchdown tool is used in the future.

66 Blocks


The photo at the right illustrates several techniques used for installation of a 66-block.

Mounting and Basic Cable Routing

Blocks should generally be mounted on a plywood back board for structural stability. (This is also true for 110 blocks.) A 12″x24″ piece of 3/4″ or 1/2″ plywood is ideal and may be available “pre-cut” at some “home improvement centers”. The back board should be at least 18″ wide to attach to two adjacent vertical wall studs (normally 16″ on center) for strength and a 24″ width allows some flexibility on lateral position. A height of 12″ allows enough vertical space for a block and wire management mushrooms. The 12″x24″ size also allows space for one or two blocks, plus space for mounting other items such as a DSL splitter and a small modem/router. Cables can be brought to the block from above or below (or both). Cables are routed out the side of the “type 89” bracket and to the side of the block.

Wire Management Mushrooms

Plastic wire management distribution posts, often called mushrooms, help control the cross-connect jumpers. This isn’t a major factor for a single block installation, but becomes very significant when multiple blocks are used.

Bridge Clips

Bridge clips are used in place of a cross-connect jumper to connect the left and right sides of the block. They can be very useful for quick repeated disconnect/reconnect for testing or to limit line access on a planned repeated basis. They can also reduce the complexity of jumpers required for an installation. The bridge clips in the photo at the right replace two jumpers (white/blue and white/orange) that would have gone over the top of the block. Another pair of bridge clips could have been used to replace the white/brown jumper that does go over the top.

This photo is of a block wired as described on the page DSL Splitter at the Hub except that bridge clips are used to connect pair 5 to pair 30 and pair 6 to pair 31, instead of jumpers over the top of the block. With the bridge clips in place, all jacks would have access to both line one and line two. By removing the first two bridge clips, the jacks connected to the cables on the left side of the block would only have access to line two. By removing the second two bridge clips, the jacks connected to the cables on the right side of the block would only have access to line one.

Wire Punchdown


Original 66-block design was for individual wires to be routed through the block’s comb one wire per comb slot, as shown on the right in these photos. Technology has evolved and it is now known that CAT5 and higher quality specification are better maintained by routing twisted pairs through one comb slot and then terminating the wires without untwisting the pair any more than necessary, as shown on the left in the photos. Fanning pairs into the block like this requires an adjustment for technicians used to the old method. It requires rotating the punchdown tool between punching the tip wire and punching the ring wire, so it takes a little more time than the old method. This new method is not necessary for CAT3 or lower quality cable. If you are terminating cable that will only be used for phone on a 66 block, you may use either method even if the cable is CAT5, since phone lines do not require the same specifications as high-speed data lines. Even if the cable will be used for modems or DSL, it is doubtful that the method of 66-block termination will have any impact on the speeds obtained. For Ethernet and other high-speed data connections, a 110-block is preferable, but this new method of 66-block termination should preserve CAT5 testing specifications.

110 Blocks


The information provided below may help you understand how you might want to configure your 110 block installation. However, the Siemon and Leviton installation instructions for 110-blocks do an excellent job of covering the basic mechanical process of 110-block installation and cable termination. I don’t believe it would serve any purpose for me to repeat the information it contains, so please refer to it also.

Additional 110-Block Wiring Information

The Leviton instruction refers to removing the block from the legs to facilitate routing cables to the block. Blocks for 50 pairs and 100 pairs may have permanently attached legs that can’t be removed as described. As noted in the Leviton instruction, removing the legs is not really necessary for these smaller blocks, since the block is not large enough to present problems routing the cables. This is a different matter in large commercial installations involving 300 pair blocks or a large field of 100 pair blocks, in which case removing the blocks from the legs can be a big help.

The Siemon instruction for 110-blocks describes routing cables through holes in the back of the block. Some blocks do not have these holes, in which case cables are routed around the edge of the block as described in the Leviton document. I don’t know of any significant advantage of having the holes. In large installations, some technicians won’t use the holes even if they are present, so that cables can be routed in a consistent manner even if some blocks are used that don’t have the holes.

Cables are normally routed into the trough between odd and even rows and covered with a label strip. Jumper cross connects are then routed in the trough that doesn’t have the label strip. When routing cables around the sides, there are two popular methods:
1) Route six cables from each side and terminate on the positions closest to that side, three on the upper row and three on the lower row.
2) Route six cables from the left and terminate on the upper row and six cables from the right and terminate on the lower row.
Either method is perfectly acceptable. You will find it useful to use one of these methods rather than attempting to bring all cables from one side, because it will be easier to nest the cables into the trough between the rows.

Creating a Bridge Instead of Using Daisy Chain Jumpers

The Leviton document describes “daisy chaining” jumper wires on a 110-block, but also notes that it is not a common practice. It’s not a common practice because 110-blocks are normally used to make connections between two cables on a one-to-one basis, such as connecting a PBX port to a single station cable or a Ethernet hub port to a cable for a LAN connection. Residential telephone is a one-to-many connection, not one-to-one. However, daisy chaining is rather awkward to install on a 110-block while attempting to maintain twist in the jumper wires. It is also prone to pulling loose due to incidental movement of the jumpers and is nearly impossible to change without completely replacing all of the cross-connects. An alternative is to create a 110-block “bridge” for the one-to-many connection and then run individual jumpers from the bridge to each station cable. A “bridge” provides multiple connections for one signal (sometimes referred to as a “bus”). The bridge is created by running a jumper wire through consecutive pair connections in the block base (as shown in the first graphic below) and then installing c-clips just like would be done for station cables (as shown in the second graphic below). A jumper is installed from the c-clip for the cable for the incoming signal (the NID or DSL splitter cable) to the bridge to put the signal on the bridge. The station cables are installed on the remainder of the block and cross-connects are then completed by running jumpers from the bridge to the cable c-clips (as shown in the third graphic below for the first three station cables). This avoids the problems associated with daisy-chain jumpers on a 110 block. This also looks a lot neater and won’t cause odd looks from experienced technicians casually observing your installation.

A 100 pair 110-block with a 4-pair cable to the NID will support a bridge (with 21 connections) for one line to 18 station cables (or a cable to a DSL splitter and 17 station cables as illustrated below).

This series of graphics illustrates the top two rows of a 110 block in progressive stages of a DSL installation with a single pair 21 position bridge:

  • The first graphic shows the cable from the NID terminated on the first four-pair position, with a c-clip in place and the wire pair that will form the bridge seated in the block base before the c-clips are installed.
  • The second graphic shows the c-clips installed for the bridge and the cable to the DSL splitter installed with the c-clip in place.
  • The third graphic shows the station cables, c-clips, and the cross-connect jumpers for the first three stations installed.

110-bridge (1)

To support two lines, you would need two bridges, one for each line, or a bridge with two pairs that alternate. Two separate bridges may be conceptually easier to understand, but it will probably be easier to install the cross-connect jumpers by using one two-pair bridge. See the photos and descriptions for the four-line configuration below for an illustration of this configuration concept.

A 100 pair 110-block with a 4-pair cable to the NID would actually support up to 15 station cables (or a cable to a DSL splitter and 14 station cables) plus 34 bridge positions (17 positions for two lines). That would require mixing cables and bridge positions on one or two rows (depending on how you configure the block), which might be a little visually confusing, but it would work. If you actually have 15 station cables, I would recommend you consider using a separate block for the cables and a four-wire bridge (see below), to allow for future expansion.

To support four lines, you would need four bridges or a bridge of four alternating pairs that spans two rows. A 100 pair 110-block configured as follows would support access four lines on 11 station cables:

  • Row 1: NID cable and five station cables
  • Row 2: six station cables
  • Row 3: first 13 pair positions, single pair bridge for line one (white/blue)
  • Row 4: first 13 pair positions, single pair bridge for line two (white/orange)
  • Row 3: last 12 pair positions, single pair bridge for line three (white/green)
  • Row 4: last 12 pair positions, single pair bridge for line four (white/brown)
  • Or Rows 3 and 4: a four-pair bridge that spans both rows

Refer to the photos below: These photos show the block described above to support four lines at 11 stations. The separate bridges in the first photo may initially seem to easier to understand, but the four-pair bridge that spans two rows makes it easier to install jumpers. With a four-pair bridge, it is also easier to alter the cross-connect for one cable without accidently disconnecting the jumpers to another cable.


Photo-1 110 Block


Photo-2 110 Block


Photo-3 110 Block


Photo-3 110 Block

  • The first photo above shows the NID cable and 11 station cables installed with the c-clips installed. It also shows how wires would be seated in the base to create four separate bridges.
  • The second photo shows the wires for the separate bridges removed and replaced with wires seated to create a four-pair bridge that spans rows 3 and four.
  • Items to note:
    • The wires extend from row three to row four in the first four pair positions.
    • The first pair (white/blue) is extended to the 25th pair position on row three to provide an additional access point for line one.
    • The second pair (white/orange) is extended to the 25th pair position on row four to provide an additional access point for line two.
    • The 25th position access points for lines one and two can be used to extend these lines to another block.
  • The third photo shows the bridge with the c-clips installed. Note that a C-5 clip is used at the end of each row.
  • The last photo shows the finished installation, with the cross-connect jumpers installed and the label strip in place.
  • Items to note:
    • The cross-connect jumpers are simply four-pair cable with the sheath removed.
    • Jumpers could be run from cables to any bridge position, but this arrangement is the most orderly and easiest for someone else to understand in the future.
    • The NID cable and station cables in row 1 (STA1-5) are cross-connected to the bridge location in row 4 (BRIDGE 7-12) using four-wire jumpers run left or right around the closest end of the block, maintaining the natural twist of the jumpers and jumper bundles. Enough slack is left to allow physically tracing the jumper between positions.
    • The station cables in row 2 (STA 6-11) are cross-connected to bridge locations in row 3 (BRIDGE 1-6) using individual short jumpers at each pair position that dip just slightly into the trough so that there is no tension on the connection. A very slight twist is maintained in the jumper.
    • This arrangement makes the line connections to all cables identical. If you want a different line configuration at any jack, the jumpers for that cable would be altered accordingly.
    • If four separate bridges were used, jumpers would have to be run from the cables to four different locations. This would be considerably more complicated.
    • Neatness and clear labeling help achieve an installation that is less likely to have undetected errors during installation and that is more easily understood by someone required to work with the installation in the future. A finished block should give the visual impression that it was well planned and correctly installed.

If there is a great probability of needing more than 11 stations in the future, a better option would be to start with two 100 pair blocks. Put the NID and all the stations on one block and put the bridges on the second block, one per row or four-pairs spanning all four rows using a method similar to the graphics and photos above for two rows. Using a separate block for the bridge also has the advantage that if there was ever a desire to install a PBX/Key telephone system, the station block would remain intact and the bridging block would just be removed and replaced with a new block with the cables to the telephone system ports.

If you have more than one line and more than 14 station cables, you might want to use a combination of bridging and daisy chain jumpers. The illustrations below shows how to bridge the cable coming from the NID, bridge one pair to connect the voice side of the line from a DSL splitter, and use daisy chain jumpers to connect lines one and two on up to 19 station cables (similar to the 66-block in the photo above and on the page DSL Splitter at the Hub). To bridge the cable from the NID as shown, it must be routed to the top of the block in a non-standard manner, so make sure to secure it to the leg of the block with cable ties to avoid having any of its wires break from movement. Also note that when creating a bridge by running pairs vertically, every attempt should be made to maintain the existing twist in the pairs. The farther wires are run parallel in straight lines, the more likely that cross-talk will occur between the pairs. This is not a major concern in wiring a block for voice, but does become more significant if the connections will be used for modems or DSL.


Removing C-Clips

C-clips are intended to be permanently attached to the base once installed. Ideally, you’ll carefully plan your configuration and take care during installation so that you don’t need to remove a c-clip. Don’t include removing c-clips as part of your future expansion plan.

f a spare positions are available, it is advisable to consider simply abandoning positions with c-clips that you might be thinking of removing. However, occasionally you might find that is just absolutely imperative to remove a c-clip.

It is possible to remove a c-clip from a 110 block, but it’s not very easy. It must be done very carefully to avoid breaking the block row and may damage the clip (which is simply discarded and replaced). Firmly grasp the center of the clip with a pair of pliers (“Channel-Lock” type slip-joint pliers work best). Gently tilt the clip down slightly to unlock the holes on the top of the clip from the “teeth” on the top of the block row.

While pulling back on the clip to keep the top from locking back in place, tilt the clip upward slightly to unlock the holes on the bottom of the clip from the “teeth” on the bottom of the block row. While doing this, don’t tilt the clip too far and bend/break the block base row structure.

Some people find it easiest to do this slowly and others prefer a “down-pull-up” jerking motion. Slow is probably best for learning. You will definitely want to avoid repeating this process at the same location, since the block base will become stressed and more likely to crack.

Also, the teeth on the base that hold the c-clip will tend to become damaged and not retain the c-clip properly. If you have a blank space on your block, attach a clip to the block without wires and use that clip to practice, since it is easier to remove a clip without wires attached.

This information should have provided you a good idea of techniques for using a 66-block or 110-block for residential telephone installations.


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