Subscriber Discussion

Can OSDP Use Shielded CAT5/5E Cable?

UE
Undisclosed End User #1
•Mar 07, 2018

Hello,

I was quoted by an access control installer for a job. Part of the job was that we utilize OSDP readers and compatible controllers. The solution presented was HID iCLASS SE readers and Mercury EP1502/MR52 controllers.

Turns out they didn't quote out the right cable. OSDP isn't meant to run over the same cable as Wiegand. The recommendation in Mercury and HID manuals is for an "RS-485" cable for both the Mercury communication wiring and reader wiring. Something like THIS or THIS. Single twisted pair, 24AWG, and shielded. The problem is this cable cost $2/ft! And all the RS-485 cable I can find seems rather expensive. To me it looks like this should work fine with CAT5/5E/6 shielded cable. Does anyone have experience with this or know the answer?

The biggest difference I found from my googling was that RS-485 has a 120 ohm impedance vs 100 ohms with CAT. However the general opinion I found was that this wasn't really relevant or meaningful in 99.99% of applications. And I read at least 1 person say they use this instead for access control and cameras when RS-485 is recommended without any issue.

This is an unfortunate situation. We had gone over this quote for the past 3 months. A few weeks ago paperwork was signed and at least some money was exchanged. I requested some minor alterations unrelated to this cabling and that didn't alter cost while we waited for HID to issue us an Elite Key. No work has been done yet. I get an email telling me they made a mistake with the quote (the same one for the past 3 months) and needed to add the cost of this cable. A 17% increase in the quoted price. I'm trying to salvage the situation before it turns for the worse.

U
Undisclosed #2
•Mar 07, 2018

It is not exactly true that OSDP doesn't or can't use the same cable as Weigand. We have literally thousands of readers in that exact setup. There are some restrictions with distances and the possibility of needing to add a resistor, but overall, there should be no concern with using a standard 22awg or 18awg shielded wire for OSDP. We use a lot of Belden 6304FE .

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UE
Undisclosed End User #1
•Mar 07, 2018
In reply to Undisclosed #2

Thanks. We would be using OSDPv2 with SCP, not sure if that might be more demanding. Most of the doors look like a 30ft run, with one being more around 60-70ft.

I read that about using Wiegand wiring in the note of the HID iCLASS SE installation guide.

Note: It’s possible to reuse existing Wiegand wiring for OSDP, however, using simple stranded cable typical of Wiegand access control readers is usually not meeting the RS485 twisted pair recommendations.

Note: For OSDP cable lengths greater than 200ft. (61M) or EMF interference, install 120Ω +/- 2Ω resistor across RS-485 termination ends.

I figured if Wiegand wiring can work, using something much closer should work fine. Then again I don't have the experience to say so and figured I should ask. The recommend wiring for Wiegand isn't even twisted pairs so I figure a 22 or 24awg shielded twisted pair cable should work wonders.

Also, are you just using the Belden 6304FE for the data? Or also power?

Curious because Mercury says to use;

RS-485 signaling requires two 2-conductor cables. Use one cable for power (18 AWG) and one cable for communication (24 AWG, with drain wire and shield)

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U
Undisclosed #2
•Mar 07, 2018
In reply to Undisclosed End User #1

There are a number of factors at play here.

The dirty little secret that no one will tell you from any of the manufacturers unless you press them is that rs-485 is actually much more robust in terms of communication then Wiegand. The key is that rs-485 allows for substantially longer distance cable runs than Wiegand, so the specifications that you will see are built for a lot of those longer requirements. Off the top of my head, I believe that rs-485 can go up to 4000 feet which is obviously much longer than Wiegand. Additionally, rs-485 allows for "daisy-chaining" of readers, which obviously cannot happen with Weigand. Those are the scenarios where I would be concerned about using the twisted pair cable. In cases like that with exceedingly long runs and multiple hops, the possibility for crosstalk and other issues is definitely much higher. However, I can say unequivocally that using standard stranded cable is more than sufficient for any osdp run that you would also consider for a Weigand run (ie <500 feet). Any manufacturer would tell you the same. 

Every one of our OSDP installations uses standard stranded, non-twisted, shielded cabling without any issues whatsoever. We provide power and data through the same cable as well. 

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UE
Undisclosed End User #1
•Mar 08, 2018
In reply to Undisclosed #2

Thanks. We've worked it out with the integrator. The sales manager talked with their technicians and HID and they are inclined to agree that while RS-485 might be the "correct way" for our needs the standard cable they run for Weigand (22/6 shielded) should work just fine. No additional cost necessary.

The education side of me would still like to run tests using both types of cable (Weigand and shielded CAT5E). Test for reliability and capability. Run long cable lengths, say 1500', and work back to shorter runs. Rig up a little machine with a counter to present the credential to the reader and let it run constantly for a while and compare the findings. I suspect the CAT cable would work better and probably costs less.

Although I'm not sure it can carry the necessary power or that you would want to send that over twisted pair anyway. I'm not even sure how much power goes to the readers actually.

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UI
Undisclosed Integrator #3
•Mar 18, 2019

This is an interesting thread and I have had an situation come up in Germany where a local supply chain officer is specifying CAT 6 cabling as a replacement for Belden type RS485 cabling. They state that the law does not allow for RS485 or maybe they have a thing with Belden cable or something.  Has anyone experienced installations in Germany that has specific regulations on cabling of RS485 buses.

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Brian Rhodes
•Mar 18, 2019
IPVMU Certified

This is very interesting.  I'll ask OSDP (SIA's group) and HID for feedback on this.

In the past, OSDP has been explained to us as a 'retrofit' upgrade that uses existing UTP cable (often used for Wiegand protocol transmission for readers to controller), but not non-UTP 'Weigand' cable,  a rare type in 2019 that was originally spec'd back in the 70's & 80's for 'Weigand' wire cards.

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U
Undisclosed #4
•Mar 22, 2019
In reply to Brian Rhodes

following...

U
Undisclosed #5
•Mar 22, 2019

I have had this exact conversation with HID a while back and did some research as well. The general rule of thumb is you can use Wiegand cable to switch to OSDP so long as the cable was within the 500' distance limitation.  Cypress has a great article on which cable types would work with OSDP which basically states almost anything.  Here is a link to the article: http://www.osdp-connect.com/end-to-end-osdp--door-panel-secure-channel.html 

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