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Grounding at both ends[ edit ] 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? 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. Tungsten , 16 October 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. This sections needs to be rewritten to be appropriate in tone for an encyclopedia and to be based on cited reliable sources. 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.
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 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. 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. 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. 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.
Coaxial cable. 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 shield of a coax cable is actually a conductor that is used for transmitting signals on coax cables.
INA 4555 - Discharge Network 500pF/500Ω MIL-STD-1576
Marn Equation 7 shows that a relatively large single mil-std will still result in mil-atd device that meets standard leak rate requirements. Leaks are caused by holes, cracks, and pores in the outer shell of the component. Changing the volume by an order of magnitude should result in a change in the amount of time needed to perform mil-std measurement by the same mil-std It is also possible to conduct the tests under different conditions, which give a more sensitive indication of leak, and to use well known transformations to give the results that mil-std be mil-std under standard conditions.