Talk:Shielded cable

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Question not addressed by article

I am an electrician at a major steel company. I occasionally work with high voltage shielded cable and am curious as to why a semiconductor material is usually used in between the cable insulator and the cable shielding. — Preceding unsigned comment added by [[User:{{{1}}}|{{{1}}}]] ([[User talk:{{{1}}}#top|talk]] • [[Special:Contributions/{{{1}}}|contribs]])

The Semiconductor (Semicon) is used between the Shield and Insulation on Low Voltage cables and between the Conductor and Insulation and between the Shield and Insulation to help "smooth out" the voltage stress caused by higher voltages. High voltages will damage the insulation by creating stress in the insulation - basically ripping the insulation at the molecular level - the stress is greatest in Corners and sharp radius turns - the Semiconductor provides a slight buffer - rounding out the area of the stress.. The reason this is applied on the shield side in Low Voltage cables - is that the shield typically sees higher voltages than the conductor- these are created by gound currents and voltages as well as disturbances such a lightning.

Paul.J.Moore 21:41, 15 August 2006 (UTC)Paul.J.Moore[reply]

Grounding at both ends

The article mentions that the shield of signal cable should only be grounded at the source end. I know this has been common practice for years for many years, but there has been some new thought in this area.

The original reason for only grounding on one end was to eliminate "ground loops" or common mode hum, on audio circuits and the like. Line frequency would get onto the audio (and now network) circuit and screw up the signal. That is a good fix for that problem and it works. However, the better solution is to fix the grounding of the overall installation so that nothing is leaking to ground in the first place.

The cable shield works best when the signal lines are completely surrounded by a conductive "tunnel" that is completely at ground potential. That means it should be grounded at BOTH ends (grounded at one end means the other end is similar to an antenna at some frequencies). But to prevent ground loops, both devices have to be at the same ground potential (otherwise current will flow on the shield). That means lots of high quality ground straps between both ends. Think of it this way, if everything in the installation were sitting on a 12 inch slab of pure copper, and bonded to it, how could a ground loop arise? It couldn't, as long as all the components in the installation are connected correctly and have not failed. In a real world application, the real solution is to reduce the slab of copper and the bonding to something practical (lots of conductive straps between all components), and to watch that all components are installed correctly and to the same standards. This is the infamous Multipoint Ground.

Cutting the shield at one end works when you have an installation with uncorrected problems, but it is not the best way to shield a signal cable. --Wolfram.Tungsten 18:47, 16 October 2006 (UTC)[reply]

In single conductor signal cables the shield may act as the return path for the signal and is usually connected only at the signal source. In multiconductor cables the shield should be grounded only at the source end, and will not carry circuit current.

what end should be connected where depends entirely on the circuit design
fwiw it is more common to connect at both ends
to suggest that only one much used method is the one that a designer or user 'should' use is simply wrong.

86.4.152.167 (talk) 20:50, 26 January 2009 (UTC)[reply]

Grounding Cable Shields

There is a very good reason why ordnance standards require wire and cable shields to be grounded at both ends. (reference: MIL-HNDBK-1512, MIL-STD-1576, MIL-STD-1542, among others) To use lightning as one example for grounding at both ends disregards the need to do so in almost all applications. Grounding at one end only to prevent groundloops has gone to far into EE designer folklore, so much they will ground coax signal cable shields at one end only with distastrous results. Grounding at both ends is the only way to intercept magnetic fields and reduce their coupling to the interconnecting wires. When not grounded at both ends, the shield does nothing until the frequency hits the quarter wavelength of the shield length and then will resonate and create a larger voltage on the wires than if there was no shield. There are specific cases where shields should be grounded at one end only but not as a general rule. —Preceding unsigned comment added by Larry A West (talk • contribs) 17:40, 22 June 2010 (UTC)[reply]

A cable/wire shield grounded at one end only is not a shield. Rather, it is a low pass filter to magnetic fields and a high pass filter to electric fields. Larry A. West — Preceding unsigned comment added by 99.116.245.154 (talk) 07:03, 23 February 2013 (UTC)[reply]

Mr. Larry A. West asserts that a shield grounded at only one end is resonant to RF frequencies at its quarter wavelength and will induce voltage to internal conductors at that frequency. He neglects to mention that a shield grounded at both ends also has resonant frequencies and can induce voltage to its internal conductors. No configuration of grounding results in the shield always being a low-impedance path to ground across its entire length, for anything but DC and low frequencies. There will always be high-voltage points and null points across its length, for any frequency with a wavelength approaching or smaller than 4 times the circuit length, where the circuit includes the ground path between both ends of the shield if the shield is connected at both ends. Grounding both ends of the shield simply increases the circuit length, creating a loop with external conductors, including conductive soil, this makes the circuit more vulnerable to lower frequencies than it would be otherwise, and admits additional possibilities for lightning currents to be introduced onto the shield. And you can't count on the conductors being balanced such that induced currents oppose each other across the length of the circuit.

So, you can't win whichever way you ground the shield. You must also consider that conductive ground is not a perfect sink to RF currents, and induced lightning voltage across the ground is a possibility with nearby strikes.

This is one reason for use of optical fiber, especially in areas where lightning-induced currents or RF interference (emitted or received) is a problem. But we eventually transition to copper or aluminum at the ends of fiber runs. We must then consider lightning-induced currents and how to shield them. The frequencies are generally low, and energy is generally distributed across frequencies with a 1/f characteristic: more energy at lower frequencies. In this case, grounding the shield at both ends can indeed cause a shield that would be unresonant if single-point grounded to conduct significant energy. Ferroresonant chokes are ineffective during lightning strikes because they saturate. In problem areas, shielded wires are further protected with metallic conduit.

So, I'll be using single-ended grounding for my application, if for no other reason than that it removes many unknowns from the equation. I suggest that those who wish to do otherwise actually attempt to model the circuit for its RF resonance and potential for induction of lightning current, using NEC or similar software. Bruce Perens (talk) 15:24, 3 July 2018 (UTC)[reply]

Is coaxial a type of shielded cable?

I don't believe that it is considered to be. If it isn't, then this photo should be deleted from the article.

--Wyn.junior (talk) 15:47, 4 March 2014 (UTC)[reply]

Coax cable is definitely shielded. The shielding on a properly constructed coax cable gets crimped to the end connector.

Coax cable is not shielded in the nature that makes it relevant to this article. The shielding being talked about for this article is the shield of data and audio cables which is there to mitigate EMI and other noise that can be induced onto the cable, or armor/shields of outdoor cables used for physical protection. The shield of a coax cable is actually a conductor that is used for transmitting signals on coax cables. — Preceding unsigned comment added by 66.90.224.212 (talk) 18:56, 17 June 2019 (UTC)[reply]

40.135.74.114 (talk) 13:47, 30 September 2016 (UTC)CipherTheTerminator[reply]

Yes, Shielded. Coax Cable is designed to transmits radio signals with the shielding grounded to the source and/or grounding block. In traditional CATV designs the COAX is grounded at the pole or pedestal at the street and at the house using a ground block bonded to the home grounding rod per NEC code. Other applications of COAX, like high power speaker cables, is a misuse of COAX and would be better served by twisted cables. — Preceding unsigned comment added by 2601:601:9280:2360:46F:8A4F:7009:3DD5 (talk) 16:20, 5 September 2019 (UTC)[reply]

Unencyclopedic section lacking citations

The section 'Practical guide for shielded cables for industrial signal applications' is not encyclopedic and lacks citatations of sources. See Wikipedia:Verifiability and "What wikipedia is not" Wikipedia:What_Wikipedia_is_not#Wikipedia_is_not_a_manual.2C_guidebook_or_textbook. The title says it all in its use of the word "guide" and exhortations to the reader to do this/don't do that. This sections needs to be rewritten to be appropriate in tone for an encyclopedia and to be based on cited reliable sources. 83.105.29.229 (talk) 12:29, 26 November 2008 (UTC)[reply]