Dual XPR522 Informações Técnicas descarregar pdf (Página 27)

Revised May 15, 2006

Using Main and Intermediate Distribution Frames

When designing a Class Connection intercom system distribution, serious

consideration should be given to using a technique of main and intermediate

distribution frames. A main distribution frame (MDF), required in every

distribution design, is simply a location in the school where the main Class

Connection intercom equipment will be installed.

Typically, the MDF will contain either a 19” rack or a wall rack for housing the

system cards, one or more power supplies and some number of 66 type

connection blocks mounted on a ¾” plywood backboard. The 66 blocks connect

to the system cards via Amphenol terminated 25 pair cables. These 66 blocks

provide connectivity to all of the speaker outputs; call button inputs, music inputs,

switch inputs, relay outputs and administrative ports.

In non-VoIP applications, each common and talkback area (classrooms, etc) in a

Valcom MultiPath system will ultimately need to be directly connected to these

blocks.

One technique for accomplishing this is certainly to homerun discrete cables from

each classroom and common area directly to the MDF. This technique, although

electrically sound, is not however, recommended.

The recommended technique involves using a series of strategically located

intermediate distribution frames (IDFs) along with the MDF. With this technique,

the MDF’s 66 block connections are distributed to centrally located closets.

These IDF locations typically contain ¾” plywood backboards and additional 66

type blocks. The distributed cables terminate on these remote 66 blocks.

Discrete cables from the common or talkback areas in the general proximity of

each IDF terminate on these remote 66 blocks. The IDFs may also contain

volume controls and power supplies for common zones.

In addition to better wire management and labor savings, IDFs provide a

convenient point to monitor for audio should system trouble shooting become

necessary.

In 45 ohm and self amplified systems Connections from IDF locations to

the MDF may be accomplished via 25 pair feeder cables or individual 4 pair

cables. Due to variations in the quality of 25 pair cables, the safest choices for

IDF to MDF connectivity are individual 4 pair cables. 25.5-volt speaker

connections should be made with appropriately sized shielded wire. 20 AWG is

adequate for 25.5-volt speakers used for talkback. 25.5 volt one way zones will

require wire sized for acceptable loss vs. speaker load vs. distance.

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Dual XPR522 Informações Técnicas Página 27