Field Terminated Series: Part 1
The interest in terminating the device end of 4-pair horizontal cabling with 8 position modular plugs has grown at a noticeably faster rate over the past couple of years. The key drivers that are contributing to this growing interest are a result of the increased use in building network applications.
The exponential increase of Wireless Access Point (WAP) deployment, along with the proliferation of “IoT” devices and applications has encouraged installers and end users to revisit the cabling approaches intended to support these relatively permanent devices. End devices that are considered fixed or permanent do not receive all the benefits that were the foundation benefits of structured cabling. When being developed, structured cabling standards placed heavy emphasis on the flexibility to support an array of end devices that might be expected over the planned life of the cabling. These standards outlined cabling designs that could support any new, transient or replaced devices over an 8 to 10 year span.
We are also witnessing the conversion of many commercial buildings devices and systems from analog to digital and IP addressable. The resulting migration of these devices and systems to 4 twisted pair cabling represents an additional class of equipment looking to be served by versions of communication cabling.
These market changes raise the question of whether these new devices are best served by:
- existing structured cabling design
- a modified structured cabling design
- or, device specific cabling to support new IoT devices/systems
Over the next two editions of Connecting the Dots, we will attempt to categorize and dissect some of these issues by posing and providing answers to some common questions. It should be noted that there are industry efforts underway to more formally resolve these questions but until those are completed the following may provide some insight.
First, this week, let’s define four common terms that that have a lot of bearing on this topic:
1. 8 position modular plug (also called an RJ45 plug)
The most recognized version of the 8 position modular plug is commonly seen on 4pair patch cords.These plugs are crimp terminated onto cordage or cable with factory or field crimping tools. These plugs utilize IDC (insulation displacement contacts), that both terminate the conductors as well as provide the contact interface surface for mating the 8 position jack contacts.
- The portion of a plugs contact that resides inside the plug is the IDC element. This side pierces the wire insulation and makes low resistance contact with the internal copper conductors (stranded or solid). In many cases the piercing contacts are in separate planes in order to straddle the conductor in an effort to increase contact area, maintain a spring force onto the conductor and possibly achieve a gas tight connection.
- The outward face of the contact, external to the plug, provides a smooth gold plated surface that will mate with the gold plated surface of a modular jacks 8 contact. These plugs require the individual conductors to be arranged & positioned in a T568A or B wiring format before insertion into the plug. The plug is then crimped, seating all 8 contacts into their aligned conductors.
One negative result of this wire positioning is the splitting of the pair going into plug positions 3 & 6. The conductors of the pair going into position 3 & 6 straddle the blue pair which resides in plug positions 4 & 5. The imbalanced positioning of these 3&6 and 4&5 pairs is critical and has a significant impact on the terminated plug performance.
There is a second type of 8 position mod plug that is designed to be more easily terminated by a field installer. While these plugs cost more than the standard plugs, the labor savings and improved performance control lend themselves to termination by an installer in the field.
These plugs will typically utilize a termination method that is easier to view & manage in a field installation environment. Many times the wire termination used in these plugs will be similarities to a lacing cap jack termination that are common in the field. This allows the wire positioning to be more easily viewed and arranged.
These plugs can also include (PCBs) printed circuit boards that connect the wire termination to the plug contacts that mate with the jack contacts. These PCBs serve two purposes. One is they allow paired conductors to be terminated next to each other saving time while reducing wiring errors and avoid splitting pairs. PCBs can also be tuned to eliminate noise sources that can be introduced with a plug termination.
2. Structured cabling (today)
The most recognized structured cabling standards today are the EIA/TIA 568 standard (in the Americas) and ISO/IEC 11801 (in Europe). The rest of the world will typically associate with one or both of these. Both standards were intended to define permanent communication cabling infrastructure within a building or campus, available to fixed locations supporting a range of devices and a variety of applications of over an expected 8-10 year life. These standards define topologies, 4 pair cables and connections, installation parameters and test methods. Defined field test methods validate the final performance of the installation. Component test limits (verified by the manufacturer or a qualified 3rd party) are used to characterize individual elements of a link or channel to ensure these parts will serve the intended range of structured cabling applications.
3. Device or system cabling
While structured cabling is associated with the infrastructure of a location or building, the mission of device or system cabling is to support specific equipment or systems over the projected life of that device or system. Historically, device or system cabling has been offered with a variety of cables, connectors and topologies. The result, in many cases, was when equipment was replaced or decommissioned, so was this associated cabling. This is different than structured cabling which is expected to continue to be operationally available within a buildings infrastructure. As stated earlier many of a buildings devices and systems are now converting from analog to digital and IP addressable, and with that change are migrating to 4 twisted pair cabling to support these devices.
4. Direct attach cabling
Direct attach cabling is recognized within the TIA568C standard but is not expected to be permanent like structured cabling. The term 'Direct Attach' was defined as (and reserved for) connecting two pieces of equipment together with a single cable. Direct attach or “direct attach channels (TIA-568-C.2-1)” “Point to Point cabling, (TIA-942-B draft)” has been used to describe equipment port to equipment port cabling. It is comprised of a single length of terminated cabling that can plug/connect directly into equipment or transceivers. This cabling approach will typically reside in the Equipment Distribution Area, or Data Center. For example, the top of rack or end of row or between transceivers. While it is more common to see direct attach cables deployed in data-centers, they can sometimes be used in enterprise spaces, typically within a closet.
In the next edition of Connecting the Dots, we will attempt to pose and provide answers to some increasingly frequent questions to build on what was discussed in this week’s edition. Stay tuned!