Upgrade Device

There are different types of 66 blocks. The most commonly used is the 50 pair Split 66 Block.


The 66 block is normally mounted on an 89D Mounting Bracket to provide some clearance to run cables behind the 66 block.


Pins in the center of the block are were wires get connected. On a split 66 block there are 4 pins on each row. The first 2 pins on a row are electronically connected, as are the last 2 pins on a row but the 4 are independent of each other. If you connect a wire to pins 1 and 2 the signal from the wire on pin 1 will also flow to the wire on pin 2 but not to pins 3 and 4.

If you want the signal from pins 1 & 2 to flow to pins 3 & 4 you would install a metal bridge clip over pins 2 & 3.

They're normally mounted vertically but to fit larger illustrations in this article I'm going to be showing them in a horizontal orientation.

A 50 Pair split 66 block will have 25 rows of pins which allow you to punch down 50 pairs of wires, 25 on each side. With old style 4 pair (green, red, black, yellow) telephone wire you can punch down 12 cables on each side. With newer style Cat5e wire (white-blue, blue, white-orange, orange, white-green, green, white-brown, brown) you can punch down 6 cables per side.

Fins on the sides of the 66 block are meant to keep wires separated from each other. Some of the fins are slightly rounded to help you identify every 10th wire. You can write on the fin with a permanent marker or apply labels to them for identification.

66 Block Vs 110 Block

66 blocks are older style wiring blocks for telephone wiring but many telecom installers still prefer them. They're more durable which allows them to be punched down multiple times and are able to handle thicker wires that may be present in older installations.

I personally prefer the 110 blocks. They serve the same function but take up less space. 110 blocks are also more compatible with high speed networking which can save a lot of time if you want to upgrade to VOIP phones in the future. 

Durability isn't an issue for me because neither should really be reused and I like that the connections in a 110 block are in the C-Clips instead of on the base so if the connector goes bad you just replace the C-Clip, you don't have to always replace the whole block as you would in a 66 block.

66 blocks are typically screwed to a mounting board which can be a simple sheet of plywood. Above the 66 block, 2 wiring spools (mushrooms) are also installed to neatly route cross connect wires from one side to the other or between blocks if multiple are installed.

The cable coming from your phone company could be a 4 conductor (red, green, black, yellow) cable that supports 2 phone lines or it may be a Cat3, Cat5 or Cat5e cable with 3 or 4 pairs of wires, each pair supporting 1 phone line.

All cables should come up through the bottom of the 66 block and then pulled out the side.

On a 66 block incoming wires are typically punched down on the left side of the block starting from the top.

Each wire is punched down to the first pin in a row with one wire per row. The order of the pairs is blue, orange, green and brown with the white wire from the pair being punched down on top. That's white-blue, blue, white-orange, orange, white-green, green, white-brown and brown.

Untwist each pair only as much as you need, pass it through a fin then hook it onto a pin from the top down. After you have all the wires from a cable on the pins, punch them down using a punch down tool with a 66 blade.

Now it's time to connect our premise wiring, the cables that run from our distribution point to the phone jacks throughout the house. These cables will be punched down on the right hand side of the 66 block using Cat5e cable. Each cable is going to use 8 pins and the order of the wires is again going to be blue pair, orange pair, green pair, brown pair with the white wire of each pair on top. Even though you may not use 4 lines in each cable it's still good practice to punch them all down.

I've highlighted the different cables with an orange box to make it easy to see in the illustration. Each cable will run to a different jack to allow one phone to be connected to it.

Right now our incoming lines aren't connected to any of the phone jacks since we're using a split 66 block. There are a number of ways to send the signal to each jack but the preferred method is to use cross connect wires to duplicate the signal to other pins on the left side of the block. This allows you to use bridge clips when you want to send a particular line to a phone.

We'll start with the blue pair, line 1.

Start by attaching the wires to the second pins where you punched down the incoming phone lines (left in illustration) then loop the cross-connect wires and and out of the fins so you can hook them around every 8th pair of pins as shown.

Keep the twists in the cross-connect wires as much as you can. For the illustration they're untwisted for clarity.

When you punch down the cross connects you'll need to switch to a non-cutting 66-blade in your punch down tool so you don't trim the wires when you're creating the daisy chain above.

If you have multiple incoming phone lines, repeat the daisy chain process for each line or all the punched down wires so you have them if you need them.

The jacks still aren't connected to the incoming lines but we'll do that right now.

In our example we want to send line 1 to all of our phone jacks. To do so all we need to do is insert a bridge clip between pins 2 & 3 for all the blue pair wires. 

Each phone is now connected to line 1 from the phone company.

If you want to connect other lines to phones, insert a pair of bridge clips to the corresponding pair of wires.

Using bridge clips is the best method but sometimes you may want to do something a little different like have incoming line 2 be the line that a phone sees as line 2. 

For example you have a home office and you only want your office phone line to be connected to that phone. Instead of using bridge clips you'll use cross connect wires coming out of the left side connected to pins 2 of an orange pair, looping around the top of the mushrooms and then punched down to pins 3 of the blue pair that leads to your office phone.

If our office phone was the second cable on the right, instead of using bridge clips our cross connect would look something like this.