Rs485Post104

TableOfContents

http://groups.google.com/group/comp.arch.embedded/browse_frm/thread/22511591b16678dd/4184893c4c3f9888?lnk=st&q=RS485&rnum=1#4184893c4c3f9888

Paul Keinanen says the same about signal grounds than Computer Journal article on RS485: In this configuration only two wires are required. No signal grounds wires nor any connection to local frame ground are required, but the transceiver supply must be floating. The problem with this system especially in multidrop systems is that the terminating resistors are at the end of the bus, but the bias resistors must be used at each station and are effectively in parallel, loading the bus. This may limit the number of stations connected to the bus.

Post 116
Steve E. Bennett



There is currently some discussion on AES48.



This document is on Industrial Ethernet.

http://www.graybar.com/Industrial/Industrial_Networking/whitepapers/B...

This one is a facilities departments standard.



So, there is plenty of material there that states that the signal cable shields shall only be connected at one end. Like I have stated before, each situation should be carefully considered, calculations performed, safety assessments performed (yes, even for the simple audio lead between intercom units) and the complet circumstances fuly understood before you go in with a half baked notion of what is right. Circumstances can change things quite drastically. You just need to understand the underlying physics of the situation a bit. http://www.electric-boat-association.org.uk/

Post 117
Here's a blurb on equipment to test the ground and shield continuity at comm cable splices (where you are saying grounds don't exist). * http://www.tequipment.net/WilcomTeleTransT124.asp Here are a couple of specifications for terminating cables to building ground systems: * http://www.nrao.edu/evla/geninfo/memoseries/evlamemo41.pdf * http://www.fac.ilstu.edu/Facilities_Services/Fac_Plan_Home/DesignGuid... Here's short URL for that last one, * http://tinyurl.com/b9gu2 Here's an even more authoritative treatment of grounding, * http://www.usda.gov/rus/telecom/publications/word_files/1751f810.doc All of these describe the grounding at *both* ends of a cable.

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Notes post 116 and 117
Both post 116 and 117 Floyd L. Davidson and Bennett would agree that grounding inside a premise at only one end is a simply fast convenient way of avoiding ground loops and other noise. But if CPE are seperated across the road Davidson says that both sides must be grounded. Bennett and Steve at fivetrees http://www.fivetrees.com disagree, they say it must always be grounded at only one end.

Links
* http://www.svconline.com/news/avinstall_implementing_electronicsystem...> * http://www.aes.org/standards/b_comments/comments-draft-aes48-xxxx.cfm> * http://www.graybar.com/Industrial/Industrial_Networking/whitepapers/B... * http://www.utsystem.edu/fpc/docs/electrical_mechanical/electrical/16120 * http://www.tequipment.net/WilcomTeleTransT124.asp * http://www.nrao.edu/evla/geninfo/memoseries/evlamemo41.pdf * http://www.fac.ilstu.edu/Facilities_Services/Fac_Plan_Home/DesignGuid... * http://tinyurl.com/b9gu2 * http://www.usda.gov/rus/telecom/publications/word_files/1751f810.doc