20 Practical Cabling Tips for Network Engineers
I think that most Network Engineers have forgotten or don’t know about network cabling. Things that I have learned, the hard way, in twenty years of looking after networks.
I find that most engineers think that cable is simply plug and play. And, mostly, that is true. In recent years, Ethernet standards and manufacturing have developed into reliable and “good enough” but the realities are still in place. Cabling needs some care and attention to detail to be reliable.
The Forgotten Things.
1. Cable Length Matters
The EIA/TIA standard says a 100 metres is the maximum cable length. THIS INCLUDES PATCH LEADS. If you are using 10 metre patch leads at each end your horizontal cable run should be only 80 metres. If you have 20 metre patch leads then you can only have 60 metres in the wall.
2. Long Patch Leads Can be a Bad Idea
You can go longer – it might work. It’s more likely to work if you have good quality cable and connectors and a well executed cabling system since the electrical signal will degrade less in that environment. Cheap installs are more likely to have problems.
That’s why long patch leads can be a bad idea in some places in your office work just fine. And in other places they don’t. A 150 metre cable run probably won’t work, or worse, won’t work reliably.
3. Overloaded Cable Trays
Cable trays should not be overloaded. Suspended cable trays are mounted to something – either ceiling mounts or support from a rack underneath. If it’s too heavy, they can fall off the wall/ceiling etc. On to expensive things. That break.
4. Leave Space to Remove Unused Cables
Too many cables is not only a safety problem, but leads to poor operational practices when people stop removing cables from trays because it’s too hard or fear of disturbing cables.
5. Crushed Cables in overloaded cable trays.
Cables at the bottom of cable tray can be crushed by weight of cables. This especially applies to Cat6 cabling which is thicker and heavier than previous copper cabling. Cables which have been crushed will degrade signal propagation.
6. Hanging Cables will Stretch
Hanging cables within the rack means that means that gravity will induce physical stress on the copper core which will stretch and distort over time. A longer patch lead is heavier and will cause more shear stress on the cable. This will create signal degradation over time and leads to intermittent failures over time. Patch management isn’t just to keep your rack tidy, it has a mechanical purpose too.
7. Don’t pull too hard
Pulling cables can damage them by stressing the copper core. Stressing the copper core can cause stretching and thinning of the copper wire which affects the signal performance. In extreme cases it will cause unwinding of the twists in the sheath. That’s why standards specify 110Newtons as maximum draw force to be applied during installation. The cabling manufacturer should ensure that their cables are able to withstand this stress (cheap cabling is often not tested or designed, it’s just “made”).
Your cabling installer should use a force meter when pulling cable to Category 6 standards to ensure that pulling strength does not exceed to the stated maximum.
8. Electrical Conduits can’t be used for data cabling
Electrical conduits and termination boxes don’t work for Category 6 cabling because the right angle bend radii are smaller than the permitted bend radius for Cat 6 copper cable. Bend damage increases changes of cable kinking, copper core stress and leads to signal degradation.
9. Less Copper
Cheap cable has lower than standard diameter copper cores which causes signal loss and results in imperfect signal propagation. When non-standard copper cores are mated to standard cores it creates more interference because impedance mismatch causing signal reflections due to impedance mismatch.
Narrow diameter cores are also physically weaker and are more likely to snap or stretch further over time thus making them more likely to fail.
10. Cheap Patch Leads
Don’t use cheap patch cords. Again, cheaper cables often don’t quite match the standard and can cause signal degradation. Other possibilities to reduce manufacturing costs include:
- non pure copper cores,
- poor quality control over twist ratios,
- poor packaging
- sub standard sheathing
These things can all result in damaged copper cables.
More to Come…..
You can find the Second Part at Top 20 Practical Cabling Tips for Network Engineers – Part 2
Other Posts in A Series On The Same Topic
- Top 20 Practical Cabling Tips for Network Engineers - Part Two (31st July 2012)
- Top 20 Practical Cabling Tips for Network Engineers - Part One (19th July 2012)