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Making a case for Fat Cat cable

You need to look no further than Power over Ethernet and the pending PoE Plus to see why it has merit.


November 1, 2006  


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Who doesn’t love Garfield? I am not a cat person, but you just cannot resist his charms. The proposed Augmented Category 6 (Cat 6A) cable is much the same — some say it is too big, and it has sometimes been referred to as ‘Fat Cat’ cable.

But in this case its size may play in its favour, if for no other reason than Power over Ethernet.

Wikipedia defines a Fat Cat as a “rich, person who, due to ownership of large amounts of capital, is able to live easy off the work of others.”

Although this may not seem like something you aspire to, in the structured cabling world this may not be such a bad thing. I would define it as a high performance cabling system that due to its ownership of higher grade components and larger size is able to work easily with the application of more power.

I do not want to enter into a debate as to whether or not 10GBASE-T will ever be used in the horizontal for workstations. I believe anyone that tries to say absolutely what we will or will not need in the future does not have enough experience in the industry, and may not have the required objectivity to be the best client advocate.

And I do not say that because I pretend to be smarter than the next guy, but rather I have been around long enough to know better.

But what I do recognize as a real world application for today is Power over Ethernet (PoE) and more specifically Power over Ethernet Plus (PoE Plus).

The original PoE standard allows for power to be applied over the telecommunications cabling with a current capacity of 350mA per pair and a load of about 13 watts.

PoE Plus (IEEE 802.3at in development) may more than double the current capacity and load limits on standards-based cabling systems.

Some discussions have included values of up to 850mA per pair and up to 60 watts, which means that the concept of powering a laptop or similar device from your structured cabling is within reach.

Now here is where our high school physics come in. To deliver more power over cables with the same resistance and given a maximum voltage, the current increases. As the current increases, the power wasted in the cable increases, and so does heat due to conductor resistance.

Excessive heat gain may have a negative effect on the transmission performance of the cabling system and could reduce its life expectancy.

The people that contribute to the work being done in the Telecommunications Industry Association (TIA) TR-42 committee are working on identifying an ideal maximum temperature rise (without affecting cable performance).

TIA is currently examining the effects of power on temperature rise and how it relates to cable types (i.e. Categories).

There are many things that affect the temperature rise: the power being delivered over the cable(s), the size and quality of the conductors, the number of cables in a bundle (as well as how many of them are energized), and whether or not the bundles are insulated in some fashion (in conduit, through concrete etc.).

As bandwidth requirements have increased, the design parameters of cable design have evolved. Conductors are larger and cables are larger with more separation between the pairs.

Coincidentally, the enhancements that have been made to improve data transmissions also have a benefit to the transmission of power.

After reviewing some of the preliminary test results from TIA relative to current capacity and temperature limits I fully expect current and power limits to vary dependent on the type of cabling used.

Although Category 5e cable appears suitable for PoE, the Cat 6A cable is best suited for PoE Plus and Category 6 is somewhere in the middle.

The basic premise for the higher (electrical) performance of Cat 6A is that the conductors are larger with greater insulation thickness, and they are more spread out within the cable sheath.

There are applications today that go beyond PoE, and mid-span devices are already shipping that deliver power in the PoE Plus range.

They are limitless — hospitality, healthcare, retail and point-of-sale, security and video, wireless LAN to name a few and every day the list grows larger.

If you want to represent your users, consider more than just bandwidth and speed for PoE and PoE Plus are real considerations that can help reduce the clients total cost of ownership and increase performance.

If for no other reason than that, Cat 6A cabling should always be a consideration.

Henry Franc is an independent consultant and member of the CNS editorial advisory board. He can be reached at hfconsulting@sympatico.ca