If the variation in categories of Copper Cabling weren’t enough, don’t worry because the different configurations bring more headaches and decisions to make…
Cables come either screened or unscreened, and most installations use simple unscreened balanced copper cabling.
However, there are multiple options for screening available, adding complexity, each bringing something slightly different to the table…
There are two forms of shielding set out in ISO/IEC 11801, foil screen and braid screen.
What is the Difference between Foil and Braided screening?
Screening is used/specified in environments where EMI is a concern.
An overall shield provides a conductive barrier to attenuate any electromagnetic waves external to the cable.
However, shielding also provides a path where induced currents can be safely taken to a grounding point (at a termination point).
Foil Screening
Foil Screening/Foil Shielding is usually a slim piece of aluminium, providing total coverage.
The main benefit of the foil screening is the fact it provides total coverage; there are no gaps in its protection.
Because the foil is thin, it makes the cable flexible and doesn’t greatly add to the diameter of the cable (CSA / Cross-Sectional Area) subsequently meaning significantly larger containment does not need to be installed.
Sadly because it is quite thin, the cables protection does have a low flex life and it’s not hugely durable.
It also provides no mechanical strength.
Advantages
- It provides overall protection with no gaps.
- Small cable diameter
- Is often cheaper than braided a alternative
Disadvantages
- The life of the protection is reduced with large quantities of flexing
- No mechanical strength is provided
Braided Screening
Braided Screening, unlike foil screening, uses a tightly woven lattice of thin wires, usually tin or copper.
Compared to foil screening, it offers a great amount more of mechanical protection, because it is harder wearing, it’s flex life is also greatly improved.
These do however come at disadvantages, because of the woven lattice there is gaps present within its protection meaning overall protection isn’t achieved like foil screening.
And due to its harder wearing qualities, it is a lot bulkier. Slightly reducing the cables flexibility and giving the overall cable a slightly larger diameter (CSA).
Advantages
- Additional strength providing a greater amount of mechanical protection
- Strong flexibility life
Disadvantages
- Gaps in coverage
- Cable diameter is increased
- More expensive
The Different Shielded Options
Now we understand the different materials used to provide shielding, we can look at the different options.
To ensure all cable manufacturers are talking about the same specification of cable, ISO/IEC 11801 implemented Annex E and introduced the following schema.
Operating on the above schema, there are 6 common cable forms. Lets take a look
U/UTP
Keeping it simple at first, U/UTP, or UTP for short.
Following the above format, this cable is not screened at all.
It’s the most common installed cable, the cable is flexible and keeps the CSA to a minimum lowering the requirements for expensive large containment.
U/FTP
Providing some screening, in U/FTP, or FTP for short there is a screen around each individual pair.
Unlike an overall screen, the screening inside the cable helps to minimise crosstalk from within the cable itself.
This is commonly found within high-frequency cables such as Category 6A.
F/UTP
FUTP, like UFTP is also sometimes referred to as FTP.
Unlike U/FTP, its screening isn’t for each pair and just wraps entirely around the cable, encompassing all 4 pairs under one overall screen.
This aids against mitigating external influences causing EMI, this can be from a range of different devices but also other cables that are bundled together.
SF/UTP
Pulling out all the stops is SF/UTP. Combining both braided screening and foil screening into one cable provides the benefits of both.
Usually found in high interference environments, both foil and braid provide an overall shield with the pairs left unscreened.
It’s uncommon to see SF/UTP used in high frequency cables such as Category 6 and above, this is due to the lack in individual pair screening.
Therefore, it’s most commonly found in Category 5e cabling where huge bandwidth requirements aren’t present however the integrity of the signal is.
S/FTP
Moving the foil screen to between the pairs is S/FTP.
Much like SFUTP, SFTP is designed for high interference environments where external influences are a concern.
But unlike SF/UTP, also a concern crosstalk between the pairs. For this reason, it’s much more likely to be found in Category 6 and above cables.
Due to the braided screening, S/FTP cabling is usually found in installations where the cables diameter isn’t of huge concern and the cable doesn’t require huge amounts of flexibility.
F/FTP
Where F/FTP proves it’s worth is in high density applications.
In installations where both crosstalk and alien crosstalk are concerns yet cable capacity and containment are also, F/FTP is used.
Because it lacks the braiding, the diameter of the cable isn’t hugely increased and nor is the flexibility, however that doesn’t compromise it’s screening abilities.
Shielded Cabling & PoE?
While we’ve been through the EMI and mechanical strength that the various braided and shielding options bring, we have neglected to mention PoE.
PoE has become a buzzword for the industry.
Hugely gaining traction, Power over Ethernet (PoE) allows you to power remote devices such as IP Phones, CCTV Cameras and Lighting with the same cable that provides the network connection.
I’m sure you’re wondering what that has to do with shielding…
Well along with larger conductor sizes, shielding being present aids the installed cable is keeping cool.
Through laboratory testing, it’s been established that the presence of a metallic braid or foil helps to dissipate the heat.
Therefore, while it’s not the only thing you should consider when implementing a PoE ready network, a shielded system should be high on your list of considerations.
To Conclude
It’s obvious that shielding through its various means provides potentially huge benefits.
However, it does come with it’s set of challenges, especially when considering the termination and containment of the cabling.
And whilst it’s great to have a wide variety of options available… it becomes a little bit of a minefield!
Therefore, if you decide that shielded cabling is really what you need, but perhaps want some guidance in what form suits your requirements.
Give one of our team a call on 01604 422722, we’d be more than happy to help!
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