4

Is there any noticeable limitations or penalties from using inline fiber couplers, such as those in a patch panel to join multiple fiber runs together?

Currently I have switches joined together directly, which obviously works fine however I want to neaten up the install and terminate the bulk of the run in a patch panel at each end, i.e.

switch <-> patch panel <---//---> patch panel <-> switch

This I figure should work as lots of people probably do this, however I also will need to do an outdoor run between two buildings using SWA-protected fiber, but I don't want to run that all the way between the patch panels as it's expensive for the length required and surely unnecessary once the fiber is inside the buildings so I was wondering if the following would still be fine, i.e.

switch <-> patch panel <-> coupler <===//===> coupler <-> patch panel <-> switch

Where <-> is normal fiber and <=> is SWA fiber.

I figure every coupler introduces some loss in signal but would it make any noticeable difference that would cause problems?

Fiber is OM3.

  • "Fiber is OM3." If you haven't already bought the fiber I would seriously consider going singlemode instead, yes you pay a bit more for the transcievers but you are likely to be thankful when you decide in the future to upgrade to newer/faster equipment. – Peter Green Jan 14 at 10:41
  • I have some existing OM3 but I need to purchase more so it wouldn't be the end of the world to swap to single mode instead. The transceivers don't look too expensive, so I'll certainly give it some consideration. – bodgit Jan 14 at 11:50
5

You're correct, that should work.

However, you need to match

  • fiber type to transceiver type (MMF for -SX, -SRM; SMF for -LX, -LR, -BX)
  • fiber grades - mixing OM3 with OM4 is mostly OK, but OM3+ with OM2 or even older severly reduces the reach; mixing SMF and MMF extremely reduces the reach
  • surface type - APC and SPC don't mix well (can even physically damage the port)

Additionally, the total fiber run cannot exceed the capabilities of the transceiver/PHY type - with excellent termination you can get away with substantially more reach, but wear and dirt degrade the signal and reduce maximum distance. Also, each coupling costs .2 to 1 dB and reduces overall reach.

Essentially, once the total sum of losses exceeds the PHY's power budget the link becomes unreliable and fails.

4

You need to develop your loss budget. Each splice will create some loss, and you must account for that in your loss budget. If you do not exceed the budget then the cabling should work just fine. There are formulae and tables for calculating acceptable loss, and (expensive) test equipment to certify and measure the cable parameters.

When you start talking about OSP (Outside Plant) cabling, you need to understand that you are bringing the outside conditions into your building. You must follow all the applicable regulations to minimize the danger. There is a legal requirement that outside cable cannot extend more than 50 feet inside the building. You will also need to follow the restrictive grounding, bonding, and lightning protection requirements.

OSP is a specialty that many cable installers will not touch because of the legal life/safety ramifications. You should really leave that up to certified professionals who will have the knowledge, experience, and test equipment to do this properly.

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