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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, while the back will hold the connection of a much longer and more permanent cable. The assembly of hardware is arranged so that a number of circuits, usually of the same or similar type, appear on jacks for monitoring, interconnecting, and testing circuits in a convenient, flexible manner.
Patch panels offer the convenience of allowing operators to quickly change the path of select signals, without the expense of automatic switching equipment. This was first used by early telephone companies, where the telephone switchboard (a massive array of patch panels) and a large room full of telephone operators running it was ubiquitous.
Uses and connectors
They are not only used in telephony and data, but in other audio and video applications. Patch bays are used at installations where it is necessary to connect and reconnect various hardware devices, for example at technical control facilities, patch and test facilities, at telephone exchanges, broadcast studios, and recording studios.
Patch panels can have any number of different types of electrical connectors, often having a different type on the front than the back. If has a compound connector on the back and individual ones on the front, it is also a breakout box. One example is a DB25 connector used for 8-channel balanced line audio, which is split into eight XLR or TRS connectors on the front.
Patch bays facilitate flexibility in the use, routing or restoration of a variety of circuit types, such as dc, VF, group, coaxial, equal-level, and digital data circuits.
In telephony and data, the 66 block and 110 block are punch blocks often used as patch panels. These have insulation-displacement connectors for quick wiring of wires which have no attached connectors. Old switchboards used tip-ring (TRS) connectors on the front, still the most common type used now for audio.
While circuits were traditionally connected with short patch cords, in some implementations routers are now used to make the connections and handle numerous, instantly recallable configurations.
Patch bays may be easier to access certain aspects in some installations but can be more expensive. They also increase the amount of cable which makes the hum and noise rejections even more important. Patch bays are available in either balanced, which can work with unbalanced applications, or an unbalanced, which can never be balanced. Common connectors for patch bays are either ¼” (6.5mm) or TT (4.4mm "tiny telephone") TRS connectors.
Normalling
Patch bays may be half-normal or full-normal, "normal" indicating that the top and bottom jacks are wired together internally. When a patch bay has half-normal wiring, its switching contacts flow through the bottom jacks of the bottom row while connected to the top row; plugging into the output connection will split the signal. If it a patch bay is wired to full-normal, then it includes switching contacts in both rows of jacks.
References
telephony equipment | audio engineering | broadcast engineering | electrical signal connectors
"Patch panel"