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Topic:
Grounding Shielded Twisted Pair
This thread has 35 replies. Displaying posts 1 through 15.
Post 1 made on Thursday August 30, 2018 at 19:16
InVision Systems
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I have read a ton of articles and forum posts concerning shielded twisted pair. At this point I’m thinking something is wrong with my reading comprehension 😜

We are utilizing shielded cat6 for a video distribution project per manufacturer’s recommendation (wire is in the wall already). A part from the “don’t use stp” advice, I’m looking for a dummies version of how to properly ground the runs. I understand that you only ground on one end and we have shielded cat6 patch panels on order that ground to the plate, run to the rack, and I understand that you’ll want to ground the rack to earth ground (we plan to ground the rack to a nearby electrical service panel).

Given what I just wrote, how does one accidentally ground the other end of the run (at the display side)?

Last edited by InVision Systems on August 30, 2018 19:33.
Elevate Technologies
Nashville, TN
Post 2 made on Thursday August 30, 2018 at 23:01
Ranger Home
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What manufacturer says use shielded? Many dont recommend it.
Post 3 made on Thursday August 30, 2018 at 23:44
Ernie Gilman
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In a conversation with Brent McCall, he mentioned to me that "shielding introduces its own problems." We didn't discuss it.

As far back as movie audio racks in the 50s,* cable shields were grounded only at one end, the source end. The general idea with audio (and the reason that Monster Cable audio cables had arrows on them) is that interference picked up by the shield would go to ground at the source end, which was very low impedance, and have very little effect on the signal. If the cable was connected with the shield going to ground at the input of the following stage, signal was likely to be injected. Part of the reason it could be injected is that inputs usually are of higher impedance than sources, so are more susceptible to interference.

The only thing I can add is that there were, a few years ago, some "baluns" that required use of the shield AS A CONDUCTOR to get HD from one place to another. It was not an issue of shielding from interference. It was a matter of getting the signal there or not.

So... what's the product you're talking about? What do the instructions say about grounding of the shield?



*As a kid I had a summer job at Ryder Sound in Hollywood, where I first encountered jack panel cables made with the shields grounded at the source end. No, that was not the 50s. It was later than that. But the equipment was old.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 4 made on Friday August 31, 2018 at 09:07
highfigh
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On August 30, 2018 at 23:44, Ernie Gilman said...
*As a kid I had a summer job at Ryder Sound in Hollywood, where I first encountered jack panel cables made with the shields grounded at the source end. No, that was not the 50s. It was later than that. But the equipment was old.

By 'source end', do you mean the preamp/processor end?
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 5 made on Friday August 31, 2018 at 14:57
Ernie Gilman
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On August 31, 2018 at 09:07, highfigh said...
By 'source end', do you mean the preamp/processor end?

The answer to this seems really obvious to me. I'll try to be brief in answering.

The source end is where the signal comes from. It's not the preamp/processor and it's not NOT the preamp/processor. The exact component doesn't create the definition. The signal flow creates the definition.

If you have a BD player connected to a preamp/processor connected to a power amp, the preamp/processor is the source end of the connection of the power amp. The preamp/processor is the... let's say 'sink' end of the connection of the BD Player and the preamp/processor. Many people communicate source and sink by saying the things are connected FROM the source TO the sink.

This is not so simple with two-way signals, since signals go both ways. But even with a BD Player, with its two-way HDMI connection, the player is the source. And if a signal always goes one way on its wire, though there may be two wires (such as RS232), each has a source end and a sink end.


Sometimes we see people talk about running a connection from speakers to an amp, or from a preamp/processor to a BD Player. This seems to reflect fuzzy thinking because the direction of signal flow is such an aid in understanding (and troubleshooting!!) the systems we work with. Hell, that's the reason most schematics have the sources on the left and the sinks on the right!
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 6 made on Friday August 31, 2018 at 16:17
buzz
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"Sources" tend to have a low output impedance. "Inputs" ("Sinks" if you like) have a high input impedance in order to reduce circuit and cable loading. The low impedance tends to swamp electric field related noise injection with signal.

An extreme case would be connecting an open RCA patch cord to a Phono preamp input or a high impedance microphone input. It is likely that there will be hum and noise picked up from the surrounding area. On the other hand, it is not likely that an open speaker wire connected to a speaker will pickup enough energy to be an issue. (However, close to a broadcast radio transmitter I have experienced this with long speaker wire runs)
Post 7 made on Friday August 31, 2018 at 16:41
Ernie Gilman
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I once saw a hifi system with good components and about 20 feet of wire completely unable to reject audio from an FM transmitter. The transmitter was 1000 feet away. There was very low level audio coming from the speakers when the system was off. Fuggeddaboudit when it was on.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 8 made on Friday August 31, 2018 at 16:51
buzz
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And, it didn't seem fair that it was an FM station. It's a variation on slope detection.
OP | Post 9 made on Saturday September 1, 2018 at 05:40
InVision Systems
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Ha. Every thread on this always ends up with a bunch of the same. I was talking to a Just Add Power rep who recommended stp. We actually ran both.

Ultimately, I'm interested in exactly how the cable is grounded at termination. If I'm grounding at the patch panel, should you also utilize the ground in the RJ45 connector or keystone? I don't quite undstand how that would also be considered "grounding" unless the device plugged in utilizes a shielded port and is grounded.
Elevate Technologies
Nashville, TN
Post 10 made on Saturday September 1, 2018 at 07:13
Ernie Gilman
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On September 1, 2018 at 05:40, InVision Systems said...
Ultimately, I'm interested in exactly how the cable is grounded at termination.

"Termination" means different things to different people. To some it means putting a connector on. To some it means being sure that the proper connections are made to the proper load (of the following stage). What exactly do you mean by it?

If I'm grounding at the patch panel,

...which means what? The patch panels I've seen have multiple connectors, none of which share a ground. Each connector (RJ45 jack) has its own ground that runs through the connector but doesn't connect tony ground on the panel. Are there panels where all the connector grounds are connected together?

should you also utilize the ground in the RJ45 connector or keystone? I don't quite understand how that would also be considered "grounding" unless the device plugged in utilizes a shielded port and is grounded.

If you have a shielded cable, that gives you the option of grounding the shield. But you don't have "grounding" unless you are connected to a ground somewhere.

I'd say that, since Brent McCall has pointed out that shielded CAT cable has problems that UTP doesn't have you should always use the shield on every cable that has a shield. By "use the shield" I mean make the shielding connection an integral part of the connection scheme... which includes any and all manners of grounding you use.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
OP | Post 11 made on Saturday September 1, 2018 at 08:45
InVision Systems
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I'm interested in any of the most common terminations for cat6 (RJ45 connector and keystone port).

I believe I mentioned in the OP that I would be grounding at the patch panel (integrated ground, to the rack, and rack to the closest electrical service panel which should be earth grounded).

My question is still the same. If I ground through the patch panel (please assume this side of the cable run is correctly terminated and grounded), what does the opposite side of the run look like exactly (using an RJ45 shielded connector or shielded keystone)?
Elevate Technologies
Nashville, TN
Post 12 made on Saturday September 1, 2018 at 10:36
crosen
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On August 30, 2018 at 19:16, InVision Systems said...

We are utilizing shielded cat6 for a video distribution project per manufacturer’s recommendation (wire is in the wall already). A part from the “don’t use stp” advice, I’m looking for a dummies version of how to properly ground the runs.

Given what I just wrote, how does one accidentally ground the other end of the run (at the display side)?

Have you asked the manufacturer?
If it's not simple, it's not sufficiently advanced.
Post 13 made on Saturday September 1, 2018 at 10:59
highfigh
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On August 31, 2018 at 14:57, Ernie Gilman said...
The answer to this seems really obvious to me. I'll try to be brief in answering.

The source end is where the signal comes from. It's not the preamp/processor and it's not NOT the preamp/processor. The exact component doesn't create the definition. The signal flow creates the definition.

If you have a BD player connected to a preamp/processor connected to a power amp, the preamp/processor is the source end of the connection of the power amp. The preamp/processor is the... let's say 'sink' end of the connection of the BD Player and the preamp/processor. Many people communicate source and sink by saying the things are connected FROM the source TO the sink.

This is not so simple with two-way signals, since signals go both ways. But even with a BD Player, with its two-way HDMI connection, the player is the source. And if a signal always goes one way on its wire, though there may be two wires (such as RS232), each has a source end and a sink end.

Sometimes we see people talk about running a connection from speakers to an amp, or from a preamp/processor to a BD Player. This seems to reflect fuzzy thinking because the direction of signal flow is such an aid in understanding (and troubleshooting!!) the systems we work with. Hell, that's the reason most schematics have the sources on the left and the sinks on the right!

I was asking for a simple answer, but OK.

Does it strike you as strange that most source devices don't have a grounded power cord and receivers, preamps and some integrated amplifiers do? Ever measure the resistance from the ground ferrule on a source device and its chassis? They're often separated.

If the system is more simple and consists of a receiver with preamp out to a separate amplifier, it could be said that the receiver is the source- that's the reason I asked in the way I did. Even a preamp and separate power amp that have grounded power cords and use XLR connections can have ground a loop, under the right conditions (or wrong, depending on how the building was wired)- I worked on a house with this condition when I installed a Krell preamp and power amp, using Canare cables. Changing to unbalanced cables cured it completely.

I'm sure you have seen this- there's no single method that works in all situations.

[Link: rane.com]
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 14 made on Saturday September 1, 2018 at 11:04
highfigh
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On September 1, 2018 at 07:13, Ernie Gilman said...
"Termination" means different things to different people. To some it means putting a connector on. To some it means being sure that the proper connections are made to the proper load (of the following stage). What exactly do you mean by it?

Good point- 'terminal' and 'connector' are often conflated to mean the same thing and it's not the case. Each wire or other conductor (could be at the circuit board) is terminated and a group of terminals (such as am RJ45/RJ11, XLR, etc are in a connector although on a board, a row of connection points is often called a 'terminal strip'.

It seems that a new glossary is needed.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 15 made on Saturday September 1, 2018 at 11:09
highfigh
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On August 31, 2018 at 16:17, buzz said...
"Sources" tend to have a low output impedance. "Inputs" ("Sinks" if you like) have a high input impedance in order to reduce circuit and cable loading. The low impedance tends to swamp electric field related noise injection with signal.

An extreme case would be connecting an open RCA patch cord to a Phono preamp input or a high impedance microphone input. It is likely that there will be hum and noise picked up from the surrounding area. On the other hand, it is not likely that an open speaker wire connected to a speaker will pickup enough energy to be an issue. (However, close to a broadcast radio transmitter I have experienced this with long speaker wire runs)

I went to CEDIA in 2005 and the guy who spoke at the Audio Setup and Measurement told us that all speaker wires should be the same length and answered "Yes" when one of the guys I worked with asked if the long cables on short runs were to be be coiled up and left in the walls and ceilings. I'd like to see how well the speaker would survive if lightning suppression cabling was in the adjacent stud bay in this case.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
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