Fiber really that fragile?

[Milt Hathaway]

Because it came up today in the venue I sometimes system tech in: Is fiber optic 'cable' really so fragile that you wouldn't want it pulled through a 75' 10" diameter pipe to FOH? The cable in question was being transported on small diameter reels, so bending radius isn't the issue (running it over doorways bent it on less than a 2" radius). Is it that they fear pulling tension or for the cleanliness of the connectors? Did the touring show buy the wrong fiber for the job?

 

[Jason Lavoie]

Re: Fiber really that fragile?

The trickiest part that I've found when dealing with pre-terminated fiber is attaching to the end with your pull cord in such a way that you're not going to pop the connectors off
it can be done and it is done all the time (and a 10" pipe is obviously more than enough) but they likely don't want to take the chance of finding out too late to get it repaired

If you ask them I'll bet they had to repair it once and they're just playing it safe.

Jason

 

[Per Søvik]

Re: Fiber really that fragile?

For outdoor multi strand cable the allowed tension during installation is fairly high, but indoor thin cables typically is less than 50 pounds, so you could easily damage even with a steady pull and a yank would definitely be out of the question.
One would think that the right cable for touring would be aerial cable, those are made to withstand a lot, and probably have got real high values for maximum tension.

 

[mackerr]

Re: Fiber really that fragile?

Because it came up today in the venue I sometimes system tech in: Is fiber optic 'cable' really so fragile that you wouldn't want it pulled through a 75' 10" diameter pipe to FOH? The cable in question was being transported on small diameter reels, so bending radius isn't the issue (running it over doorways bent it on less than a 2" radius). Is it that they fear pulling tension or for the cleanliness of the connectors? Did the touring show buy the wrong fiber for the job?

Most production fiber is 4 core "Tac4" which is tactical fiber originally meant for military use. It is quite tough both for crush resistance and tension since it also has Kevlar fibers for strength. They probably just didn't want to deal with running temporary cable through conduit. That is a primary driver for investing in fiber, you can usually find an inoffensive, safe cable path without having to resort to things like pipe.

Mac

 

[Milt Hathaway]

Re: Fiber really that fragile?

Most production fiber is 4 core "Tac4" which is tactical fiber originally meant for military use. It is quite tough both for crush resistance and tension since it also has Kevlar fibers for strength. They probably just didn't want to deal with running temporary cable through conduit. That is a primary driver for investing in fiber, you can usually find an inoffensive, safe cable path without having to resort to things like pipe.

Mac

We pulled a bundle with power, coax, and a small audio snake through the pipe for them. I understand it's their choice, I just wondered about the theory behind it. Seemed to me that running it along the walls of a theater turning at least a dozen sharp corners would be more damaging to the cable over time, so that's why I asked.

I also understand the lack of trust in the local venue tech's ideas, too. I'm not bothered by it.

 

[Chris Johnson]

Re: Fiber really that fragile?

I do a lot of work with fibre as part of larger audio distribution systems, or using products like Optocore etc...

I may soon be investing in some, so I've done a lot of research and have seen/tried a lot of samples.

The answer, as with all things, is: it depends.

There are essentially 2 kinds of fibre cabling (when it comes to physical construction): tight-buffered, and loose-tube.

The actual piece of glass that the light travels through is very thin, typically 50um, so it is covered in a cladding. The combination of the core and the cladding is what you would call the 'fibre'

Now, in a tight buffered cable, the cable jacket is then bonded to the cladding. Patch cables are a good example of this.

In a loose tube cable, the fibre (core+cladding) floats inside the jacket (and armour). In proper installation loose tube cable, the fibre floats in mineral oil.

For live work, cables like the neutrik armored stuff, the fibre normally 'floats' in strands of aramid.

So, as you will immediately guess, tight buffered cable is really pretty unsuitable for live work. Because the fibre is bonded to the jacket, excessive bending, crushing or pulling on the outside of the cable can damage the internals very easily. That said, it is shocking how many hundred meter drums of tight buffered cable I see on gigs. These will not last all that long if they get the normal gig cable abuse.

Tactical cable, which is like a field-suitable version of loose-tube changes this in a number of ways. Firstly, the fibre is free to move within the assembly, so damage due to bending is reduced significantly. Secondly, you have to crush the cable a lot before you run the risk of crushing the internals. Armoured cable adds a stainless steel mesh between an outer and inner jacket, to protect against cutting and crushing even further.
If you go for tactical cable with tactical connectors, you get another benefit: typically the connector itself is attached to the aramid section of the cable. This means that pulling on the connector doesn't transfer any strain to the fibre itself. Aramid, amongst its other properties, does not stretch at all, and has a very high breaking strength.

So in short, if you buy proper cable, that is properly armoured, it will actually end up much stronger than most other cables on your jobs. And you should quite happily be able to do anything to it that you would do to a mic cable with no issues.

 

[Ryan Adkins]

Re: Fiber really that fragile?

I just got done installing 3 rooms with fiber about 60 feet apart in my recording studio. I didn't have any problem pulling it although it was pulled with audio lines so that absorbed the tension. I would at least strap it to another cable to pull.