Fiber Optic Cable tests - long haul - 1.25 miles

[buzzp]

I have been tasked with developing a fiber optic spec to supply and install some single mode fiber over a mile through existing conduit (nearly empty) with no splices. My fiber experience is next to done but I have narrowed the tests I should require down to two:

Optical Loss test or OTDR.

Seems the OTDR might be over kill since we are requiring no splices and the cable run is fairly small. If I do require an OTDR test, how to quantify a pass or fail with that test? The Optical Loss is straight forward in establishing a pass/fail criteria.

Would you just require the Optical Loss test here or if you would recommend and OTDR, how do I establish a pass/fail level in the spec.

Thanks.

 

[VEBill]

Gather up some data based on your communications equipment at each end of the link. Those equipment specs should inform you what are the acceptable limits.

Next, review the cable spec and figure out what should be achievable assuming it's installed perfectly.

Then you can split the difference. Maybe split it one-third / two-thirds in your favour since you're writing the spec. Don't be too hard on your installer as being overly tough can lead to contractual failure.

TDR testing is simply a question if you can afford to rent or buy the test set. Useful for locating faults.

Does the permanent equipment provide any feedback about signal quality? Perhaps you could use a short jumper to calibrate the permanent equipment, and then compare it when using the full cable.

Disclaimer: My experience is with RF cables. Not so much optical. We have the exact same questions about setting limits.

Ultimately it's a judgment call and depends on external factors too. Once in service, you'll tolerate more loss as long as the system works. Monitoring can track condition over time.

 

[IRstuff]

You might want to peruse:

http://www.thefoa.org/tech/loss-est.htm

and

http://www.thefoa.org/tech/index.html

and

http://www.vdvworks.com/VHO/OTDR/OTDR1.htm

TTFN
faq731-376

 

[buzzp]

I have read alot of info on the FOA website prior to posting. I don't think we will require an OTDR test as there are no splices and we don't own one of these ourselves so establishing a benchmark won't help. This is a 24 pair cable so I want to make sure it is done right before they leave. Based on my limited understanding an Optical Loss Test should proove the cable pull was done correctly along with the terminations. It won't help much in pinpointing any issues but it should be enough to pass or fail the install and termination job, agreed?

Thanks for the feedback.

 

[IRstuff]

I would agree, the link loss test will give you a gross indication of whether everything was assembled correctly.

TTFN
faq731-376

 

[robertjo24]

If you are pulling a mile of single-mode through existing conduits with no splices, I would require an OTDR test. The end to end loss would tell you a pass or fail. The OTDR would indicate any stress points in the installation.

If there were any damage tot eh cable during installation (over bending, stretching, etc), and OTDR could indicate a location that could cause issues later on.

I would also have them shoot the cable on the spool upon delivery to make sure the cable is good prior to acceptance.

 

[buzzp]

I was going to request the factory test data (I would think they would do both tests), require Loss test upon delivery and after complete installation.

My concern with the OTDR is the cost increase this could have with the contract. I suppose making this a requirement may eliminate some of the less professional cable installers from getting it.

 

[VEBill]

Risk = Profit (probably).

Applies to you too.

 

[buzzp]

Is it better to terminate ST or SC connectors in the field or get cable with factory terminations (pigtails) and just do splices in the field? Which is easier to do - splices or terminations?

This is OSP install of a little over a mile (48 fiber, loose tube, single mode)

Thank you

 

[buzzp]

Sorry meant to start a new thread with my last post

 

[robertjo24]

With an experienced installer, field installed connectors can be just as reliable as factory pigtails that are spliced.
The spliced connector pigtails may be a little cheaper on install.

Any reason you are using SC or ST connectors? They take up a lot of room. We’ve go to LC connectors and can get a lot more connections into a smaller space. You can get jumpers that have the right ends to connect equipment.

Of course, this is all my humble opinion.

 

[buzzp]

The fiber world is new to me but I selected those connectors based on what is currently there. I have talked to our IT folks and they are open to whatever I select. I did do a little research and was thinking the ST or SC were more common but maybe that was old information. I'll do a little more work there but if they are smaller then this could be an advantage here due to the limited patch panel space available. Thanks for the info.

I would be interested to here more about splicing pigtails vs. field terminating connectors (ST SC or LC). Perhaps, this should be left up to the contractor if I require both a loss and OTDR.

I think understanding the stress points, etc in the cable after the pull and before would probably be a good idea so I will reconsider the OTDR test. I just didn't want to request something that was unnecessary but I can see where this test would have some real value at least in approving the install and identifying potential future trouble spots, even though it is a relatively short run in terms of OSP installations.

 

[robertjo24]

You bring up a valid point. If you contract the installation and termination of the fiber, providing very clear requirements on the performance of the final product, then it shouldn't matter if the connectors are field installed or spliced pig-tails. The contractor will be responsible for providing the finished product to spec.

If you are providing the fiber, and just contracting the installation and termination, I highly recommend having the contractor verify the fiber integrity before it comes off the delivery truck. They can use low cost mechanical splices with test pigtails and an OTDR to accomplish this. It is worth the added expense, because once it is installed, it is hard to argue who is at fault if there is a broken strand halfway down the cable. I unfortunately know this from experience.

If the contractor is buying the cable, they will likely do it anyway. If they install the cable they provide and there is a broken strand, they have to replace the cable.

 

[buzzp]

The contractor is supplying the cable. I am going to require the test reports from the factory, testing upon delivery, and testing after installation and termination. Do factory test reports usually include OTDR and OLT? (currently just asking for factory test 'reports' with no tests specified). The pre and post install tests will be both OTDR and OLT.

I think I will give them the option of using pigtails and splicing or terminating the ends in the field. Although it means more writing for me, we can all agree a well written contract is good for everyone. Unfortunately, I have had only a week to put this together so I appreciate all the suggestions and recommendations.

 

[robertjo24]

Let us know how it goes.
Best 'o luck to ya.

 

[djs]

TIA has several standards for testing and accepting fiber cables. Specify acceptance testing against one of those standards.

On a side note, Corning cable has a program where if an approved installer installs and tests Corning cable and connectors, Corning (not the installer) will warrant the material for 25 years.

 

[Prowler6484]

Contact some of the major fiber cable providers and ask them for an install spec; most will have a generic one on hand that will make your life easier. I agree with robertojo24; have the contractor test each strand on the reel before installation and again after. The OTDR will test for any defects, including any sharp bends during installation that could cause loss. The terminal panels with pigtails, SC connections, are what I use in most installations. If you are short on real estate the LCs are fine; the STs are used in places where there is a danger of the connection coming loose. A handhole or other type of pullbox are recommended on both ends of the run, usually right outside the facility. These will provide space for slack which will be useful when splicing the cable. Make sure and provide plenty of extra fiber for slack and install a trace wire if the conduit is not metal as you will need a way to locate the fiber later.

 

[buzzp]

Thanks for all the help and suggestions. I finally got a good spec and it has been awarded. They will be providing an OTDR from the factory, upon delivery and after installation. They are required to do the same with the losses (of course the results will be a little different after termination) but I did identify what was acceptable loss and not acceptable.

Thanks again.