A punch down block is a type of electrical connection often used in telephony

Telephony

In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

. It is named because the solid copper wires are "punched down" into short open-ended slots which are a type of insulation-displacement connector

Insulation-displacement connector

An Insulation-displacement connector, insulation-displacement technology/termination or insulation-piercing connector is an electrical connector designed to be connected to the conductor of an insulated wire or cable by a connection process which forces a selectively sharpened blade or blades...

s. These slots, usually cut crosswise (not lengthwise) across an insulating plastic

Plastic

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...

 bar, contain two sharp metal blades which cut through the wire's insulation as it is punched down. These blades hold the wire in position and make the electrical contact with the wire as well.
A tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 called a punch down tool

Punch down tool

A punch down tool, also called a punchdown tool or a krone tool , is a small hand tool used by telecommunication and network technicians...

 is used to push the wire down firmly and properly into the slot. Some will automatically cut any excess wire off The exact size and shape of the tool blade varies by manufacturer, which can cause problems for those working on existing installations, especially when there is a poorly-documented mix of different brands.

Punch down blocks are a very quick and easy way to connect wiring, as there is no stripping of insulation and no screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

s to loosen and tighten. Punch down blocks are often used as patch panel

Patch panel

A patch panel or patch bay is a panel, typically rackmounted, that houses cable connections. One typically shorter patch cable will plug into the front side, whereas the back holds the connection of a much longer and more permanent cable...

s, or as breakout box

Breakout box

A breakout box is an electrical device, usually housed in a box, in which a compound electrical connector is separated or "broken out" into its component connectors. Compound connectors are used where sufficient space for connections is unavailable...

es for PBX or other similar key phone systems with a 50-pin

Pinout

In electronics, a pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions.- Purpose :...

 RJ-21 (Amphenol

Amphenol

Amphenol Corporation is a major producer of electronic and fiber optic connectors, cable and interconnect systems such as Coaxial cables. Amphenol is a portmanteau from the corporation's original name, American Phenolic Corp....

) connector. They are sometimes used in other audio applications, such as in reconfigurable patch panels.

Oftentimes a separate tool known as a spudger

Spudger

A spudger is a wiring tool used for poking or adjusting small wires or components, generally in the electronics and telecommunications industries....

 is used to remove small stray pieces of cut off wiring stuck within punch down blocks.

Reliable connections

It is possible to insert wiring without the proper tool, but this requires great care to avoid damaging the connectors. For example, pushing a screwdriver down the middle of the block is a bad practice as it forces the two blades of the terminal post apart, leading to bad contacts. It is also possible to punch down multiple wires on top of each other in a single post of a punch down block, but this practice is discouraged because of reliability concerns. If these multiple wires are of different thicknesses (wire gauges), it is even more likely that the thinner wire will develop contact problems. Similarly, stranded wire can be used on punch down blocks, even though they were originally designed for single-strand wire connections.

Marginal practices like these are strongly discouraged in large or mission-critical installations, because they can introduce extremely troublesome intermittent connections, as well as more-obvious outright bad connections. Once the contact blades in a punchdown block are "sprung apart" by poor practices, the entire block often must be replaced to restore reliable connections.

In addition, punch down blocks are being used to handle larger numbers of faster data signals, requiring greater care and proper procedures to control impedance

Impedance

Impedance may refer to:*Electrical impedance, the ratio of the voltage phasor to the electric current phasor, a measure of the opposition to time-varying electric current in an electric circuit**Characteristic impedance of a transmission line...

 and crosstalk.

Examples

• A 66 block
  66 block
  A 66 block is a type of punchdown block used to connect sets of wires in a telephone system. 66 blocks are designed to terminate 22 through 26 AWG solid copper wire....
  
   (or "M Block") is used in telephone
  Telephone
  The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
  
   systems.
• A 110 block
  110 block
  A 110 block is a type of punch block used to connect sets of wires in a structured cabling system. 110 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...
  
   is often used in residential telephone and Cat 5
  Category 5 cable
  Category 5 cable is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors...
  
   wire systems.
• A Krone block
  Krone LSA-PLUS
  KRONE LSA-PLUS is an insulation-displacement connector for telecommunications. It is a proprietary European alternative to 110.-History:...
  
   is a proprietary European alternative.
• A BIX
  BIX
  BIX is part of a telephony cross-connect system created in the 1970s by Nortel Networks. As a system, it consists of various sizes of punch-down blocks, cable distribution accessories , and a punch-down tool to terminate wires at the punch-down block...
  
  block is a proprietary block developed originally by Nortel Networks.