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Thread: BACNet wire

  1. #53
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    Quote Originally Posted by numbawunfela View Post
    I figured as much. Now that I look it does say capacitance on that field not Impedance. Woops!
    Especially with the Zo free wire having possible variance between batches - that means if Johnson tested a roll and liked how it turned out, you may not have similar results in the next roll. As you pointed out earlier, again - helpful!

    It is also good to get the data out of a link and into the thread, not everyone is interested in taking the extra 2 min it takes to follow the links.... and links go bad.
    Good day numbawunfela,

    I figured as much. Now that I look it does say capacitance on that field not Impedance. Woops!
    No worries, as I do this all the time. Sometimes will all the data available it is easy to overlook or misread something.

    Especially with the Zo free wire having possible variance between batches - that means if Johnson tested a roll and liked how it turned out, you may not have similar results in the next roll. As you pointed out earlier, again - helpful!
    This is true. Now, to be fair to JCI... not all sites "need" the proper cable, as the cable lengths/runs, site electrical noise, number of attached controllers, etc may all work together such that non ideal cable will work... and does in a number of sites. But I am confused as to why they would suggest cables that are less than ideal? When I first saw the specs (2009) I asked JCI Milwaukee for their reasoning and responses to my questions... all I heard was crickets.

    Anyway... to me I look at this in two ways:

    1. I like to use the proper and best cable, as then my customer is well positioned to have minimal or no cabled related comm issues with their current and future needs. If I use the best/proper cable then I "know" for certain the cable cannot be problem with any issues that might arise.

    2. The extra cost of the best/proper cable is relatively insignificant to the cost of installing the cable and/or the costs of troubleshooting/rectifying cable-related comm issues.

    Cheers,

    Sam

  2. #54
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    Quote Originally Posted by numbawunfela View Post
    Perhaps the 'first' issue is that the RS485 spec is open yet costs $100+.
    Whopping $93 freedom bucks.

    https://global.ihs.com/doc_detail.cf...=&org_code=TIA

    For as much as one uses 485 in this industry, seems like a pittance. Someone has to maintain it, pay for the bandwidth / printing costs.

    Note the pdf version is secured with the Fileopen plugin, same a many ASHRAE pdfs. Miserable pile of crap, requires Adobe pdf reader. Yet who wants to cut the binding off a book and scan it...
    Propagating the formula. http://www.noagendashow.com/

  3. #55
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    Quote Originally Posted by orion242 View Post
    Yet who wants to cut the binding off a book and scan it...
    I do... and have.
    This is not an invitation for people to start bothering me for a copy, I just know that my laptop will die. The license is tied to the machine that you used to first open the file. So that is a nonstarter.
    Last edited by numbawunfela; 09-15-2019 at 10:28 PM.
    Hmmmm....smells like numbatwo to me.

  4. #56
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    Quote Originally Posted by numbawunfela View Post
    The license is tied to the machine that you used to first open the file.
    Not sure how these guys handle it, but ASHRAE you can log into the bookstore and release it. Then the next PC that opens it, it becomes locked to that. Real handy for transferring between machines.

    Its a PITA, but screwing around pulling origami creations from the copier isn't something my patience can tolerate.
    Propagating the formula. http://www.noagendashow.com/

  5. #57
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    Quote Originally Posted by s2sam View Post
    We may be looking at different wiring specs, as the JCI documents I found for wiring are pretty loose with regards to RS485 communications. For example the Belden B6501FE and the 6501EU are not actually transmission line rated cables (this was taken from JCI's spec from 2009 and 2019). I say this, as they do not include a characteristic impedance (Zo) spec and so the effectiveness of the wire in a given install is in question.... so it may work fine or it may not. A cable made with a Zo spec costs more, as the components used must have the same electrical specs. The result is that every time you buy a box it will work the same as the previous box. With cables that do not have a Zo spec means that this batch of cables may have a Zo of "X" and a later batch "Y", etc.

    Secondly, these cables are not spec'd to be twisted.

    The only thing positive about the wire spec is that it includes the 3rd wire (reference) which is important for long term reliable RS485 communication. Personally and Professionally I would not recommend these wires for MS/TP, N2, or any RS485 communication bus. That is not to say that the JCI wire specs will not work, they might... but my question is why take a chance on it? The cost for proper RS485 wire is a bit more and given the risk involved the few extra bucks for proper cable is really a non issue. Another point is that if you install proper RS485 cable (and wiring practices) then the cable can be used for much higher communication rates without concern about having to reinstall different cable.
    Sam, this is where I go out and find a cable that looks good and put the part number into my RS485 cheat sheet (as I am a good figure-out-er and a bad rememberer). In the interests of self serving laziness, and also recognizing that you swim in these waters more often than I do, do you have a wire that would seem to meet the suggestions you laid out? 3 conductor, shielded, twisted with a good capacitance spec?

    I understand that any information I get from you will only be used at my own risk and I hereby do solemnly swear not to flame you on this or any other forum if it all goes horribly wrong some day in the future. ;-)
    Hmmmm....smells like numbatwo to me.

  6. #58
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    https://catalog.belden.com/index.cfm...106A,PF_3106DB
    There are 2 part numbers for 1.5 pair cables that seem to provide ratings for good RS-485 communication. Neither are plenum rated. Belden 3106A and 3106DB

    I could not find any others....
    Hmmmm....smells like numbatwo to me.

  7. #59
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    The ASHRAE BACnet standard calls out 100-130 ohm impedance (Zo) and less than 30 pf/ft between conductor cable for MS/TP. Guess if the RS-485 spec fails in this respect, the BACnet standard should rule in that specific use case.

    See 9.2.1 Medium in 135-2010.

    How audio cable that doesn't specify an AC impedance meets BACnet standard...someone will have to enlighten me.

    Far as I see, that crap is only suited to transmit the screams of agony when things don't work.
    Last edited by orion242; 09-21-2019 at 12:32 AM.
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  8. #60
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    I FINALLY bought the last rev of the BACNet spec about 3 mos ago... and then they go and update it... DOH!

    Thanks for reminding me....
    Hmmmm....smells like numbatwo to me.

  9. #61
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    Lol. have the most recent spec as well.

    Just didn;t want to hassle to release every copy though the bookstore.

    There is little standing outside their spec, which aligns with the bulk of 485 devices.

    JCI recommending special snowflake crap is just non-sense.
    Propagating the formula. http://www.noagendashow.com/

  10. #62
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    Quote Originally Posted by numbawunfela View Post
    Sam, this is where I go out and find a cable that looks good and put the part number into my RS485 cheat sheet (as I am a good figure-out-er and a bad rememberer). In the interests of self serving laziness, and also recognizing that you swim in these waters more often than I do, do you have a wire that would seem to meet the suggestions you laid out? 3 conductor, shielded, twisted with a good capacitance spec?

    I understand that any information I get from you will only be used at my own risk and I hereby do solemnly swear not to flame you on this or any other forum if it all goes horribly wrong some day in the future. ;-)
    Good day numbawunfela,

    My apologies for the delayed response, but work has been extremely busy these past several months...and so I have not had a chance to check back on here since my last visit.

    I cannot give you a RS485 part number for the cable I use, as it is custom made for the firms I work with. A number of years ago it was a gamble if a vendor had the same wire in stock and so I recommended that custom cables be made. This way all of the sites would have the same looking wire, but more importantly would behave the same as the specs would be the same. It took some convincing to get them to do this, but in the end the extra cost for custom cable has saved $1000's of dollars in lost time troubleshooting and sorting out site wiring issues. As I said since the companies have been doing this they have had 0 site wiring issues. Off the top of my head I recommended 3 conductors (2 twisted), with shield and drain, 12 pf Capacitance between conductors, and a characteristic impedance of 120 ohms. The low capacitance allows much higher data rates if needed in the future.

    Cheers,

    Sam

  11. #63
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    Thanks Sam!

    The cables I posted above got the 120ohm impedance and 11pf capacitance, and 3 conductors, shield and drain. So it looks good.

    Just not a plenum rated option. That is a little annoying.
    Hmmmm....smells like numbatwo to me.

  12. #64
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    Quote Originally Posted by numbawunfela View Post
    Thanks Sam!

    The cables I posted above got the 120ohm impedance and 11pf capacitance, and 3 conductors, shield and drain. So it looks good.

    Just not a plenum rated option. That is a little annoying.
    Good day numbawunfela,

    Understood. Give the cable part number to Windy City and see what they will charge to make you a plenum rated version.

    Cheers,

    Sam

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