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|WikiProject Electronics||(Rated Start-class, Mid-importance)|
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.
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
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 leakingto 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)
- 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.
Unencyclopedic and 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. 22.214.171.124 (talk) 12:29, 26 November 2008 (UTC)
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)
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 126.96.36.199 (talk) 07:03, 23 February 2013 (UTC)
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.
Coax cable is definitely shielded. The shielding on a properly constructed coax cable gets crimped to the end connector.