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Using a 66 Blocks for RTU Alarm Wiring and Phone Lines

By Andrew Erickson

March 23, 2023


If you're setting up a phone system or contact-closure alarm monitoring system, 66 blocks are an essential tool. 66 blocks are pre-wired distribution panels that can be used to cross connect wires and quickly set up phone lines.

What is the 4-column structure of a standard 66 block?

66 blocks provide center terminals that make it easy to punch down wires with a punch down tool. There are 50 rows on a standard 66 block (25 pairs of wires). The number "66" is merely a reference to the original part number of the original Western Electric model. It became industry slang for this particular punch-down block format.

The 66 block is split in two sides. The left side is used for incoming phone lines, while the right side connects to the phone system. The two pins on the left side and the two pins on the right side of each row are electrically connected to each other.

From left to right, you would commonly see:

  1. Incoming alarm wire or phone line wire
  2. One side of the bridge clip
  3. Other side of the bridge clip (connecting the incoming wire to the premises equipment)
  4. Premises equipment, whether that is building phone/VoIP equipment or gear with alarm outputs

Bridging clips are sometimes used to bridge between both sides of the 66 block. This helps to create a physical connection between each separated wire in the 66 block.

This "bridge" can be opened/closed during wiring work, troubleshooting, or to simply indicate which terminals on the block are currently not used.

A 66-block with an amphenol port supports connecting your alarm wires to your remote monitoring RTU

66 blocks can be connected to a Remote Telemetry Unit (RTU) via an Amphenol cable. This allows you to conveniently and durably connect your monitored devices to your RTU.

Amphenol cables contain 25 pairs of wires, so they can carry (typically) 24 alarm points and also a pair of ground wires. At DPS, that's why we use amphenol ports and cables for our large and medium RTUs. For smaller models with 8 alarm points or less, it's common to see screw terminals or something similar.

To install a 66 block with your RTU, you'll need to wire everything up in this order:

  1. Choose and install an RTU with at least one 50-pin amphenol connector.
  2. Connect an amphenol cable of your chosen length to your RTU. Choose a cable that can comfortably reach your desired 66 block placement. A longer cable is typically required for a rack-mount RTU, as most 66 blocks are wall-mounted. You'll need enough cable to reach the ceiling/ladders, travel horizontally, and drop back down to the 66 block.
  3. Choose a 66 block with an amphenol port on its side. Install this 66 block (usually on a wall).

How to plan cable length to properly reach your 66 block

When you're planning your 66 block wiring and cable length, it's a good idea to plan for an extra foot or two of cable in each direction. This helps minimize stress on the 66 block and ensures that you won't run out of cable when connecting things.

An amphenol cable will, as described above, need to follow your cable management tracks up, over, and back down between RTU and 66 block.

Alternatives to 66 blocks for alarm termination

Let's now take a look at some alternatives to 66 blocks that you might prefer to buy in certain scenarios.

66 blocks are great for connecting alarm wires and setting up phone lines, but they aren't the only option. There are other ways to terminate alarm wiring, such as screw terminals with insulation displacement connectors (IDC). IDCs provide an easy way to connect wires without having to use a punch down tool. They can also save time if you're in a hurry and don't have the time to use 66 blocks.

Wire-wrap panels are also popular. Wire-wrap panels are similar to 66 blocks, but they use a different technique to secure the wires. Instead of punching down into a constricting slot, wires are wrapped tightly around square posts. This is considered the gold standard in long-term reliability. Electrically, you have about 28 chances in 7 wire revolutions to make solid contact with once of the 4 corners of a square post. Wire wrapping is both reliable and durable.

As I mentioned above, simpler methods are available for smaller monitoring devices or non-critical applications. These can include "snap lock" terminals where you insert wire into a gate and flip a latch down to lock. Screw terminals are a more secure option that requires nothing more than a screwdriver and wire stripper for installation.

Whether you choose 66 blocks or another wiring solution, it's important to ensure your alarm wiring is connected to the correct terminals.

No matter which option you choose, always make sure that your connections are secure, reliable, and safe. Doing so will ensure that your alarm system is running properly at all times.

Who are the best manufacturers of 66 blocks?

When you need 66 blocks, it's important to choose a reliable and trusted manufacturer. Some of the top 66 block manufacturers include Leviton, Panduit, Belden, and ICC.

It's beyond the scope of this article to provide a comparison of each one, but I can tell you that 66 blocks are generally considered to be commodity items. You need to choose a reliable manufacturer, but this product type is hardly rocket science.

Focus mainly on ensuring that the mounting style (virtually always wall mount) and the amphenol (RJ21) port suit your project requirements.

DPS sells 66 blocks alongside our RTUs as a convenience, but I won't lie to you and tell you that 66 blocks aren't available at hundreds of retail websites. You can purchase them from many different online stores.

Call DPS to get clarification about 66 blocks or any other standard telecom equipment

66 blocks are standard practice for setting up phone lines and contact-closure alarm monitoring systems, so learning how to use them properly will save you time in the future.

At DPS, our engineers commonly work with 66 blocks and several other common alarm termination methods (wire-wrap, pluggable panels, screw terminals, etc.). If you need help getting started, we can give you guidance.

Call DPS at 1-800-693-0351 or email us at sales@dpstele.com

Andrew Erickson

Andrew Erickson

Andrew Erickson is an Application Engineer at DPS Telecom, a manufacturer of semi-custom remote alarm monitoring systems based in Fresno, California. Andrew brings more than 17 years of experience building site monitoring solutions, developing intuitive user interfaces and documentation, and opt...